Elucidating the origin of chiroptical activity in chiral 2D perovskites through nano-confined growth

Chiral perovskites are being extensively studied as a promising candidate for spintronic- and polarization-based optoelectronic devices due to their interesting spin-polarization properties. However, the origin of chiroptical activity in chiral perovskites is still unknown, as the chirality transfer mechanism has been rarely explored. Here, through the nano-confined growth of chiral perovskites (MBA2PbI4(1-x)Br4x), we verified that the asymmetric hydrogen-bonding interaction between chiral molecular spacers and the inorganic framework plays a key role in promoting the chiroptical activity of chiral perovskites. Based on this understanding, we observed remarkable asymmetry behavior (absorption dissymmetry of 2.0 × 10−3 and anisotropy factor of photoluminescence of 6.4 × 10−2 for left- and right-handed circularly polarized light) in nanoconfined chiral perovskites even at room temperature. Our findings suggest that electronic interactions between building blocks should be considered when interpreting the chirality transfer phenomena and designing hybrid materials for future spintronic and polarization-based devices.

6. Page 4 line 122: "intensities" is not a correct term to use here. 7. Page 6, line 148-152. I find it hard to accept the general statement made, when only one XRD peak is shown. Properly, an analysis would need to be made of the XRD patterns to actually determine the space groups before making such a broad claim: "This observation implies that unprecedented chiroptical phenomena of templated chiral 2D OIHPs cannot be explained in terms of the dichotomy between optically active chiral space group of P212121 (iodidedeterminant phase) and nonchiral space group (bromide-determinant phase) ...." 8. The analysis of micro-strain based on XRD linewidths, shown in Fig 2, is described in the SI in Supplementary Note 2. There the authors state that Scherrer broadening is neglected since chiral OIHPs "have grain size larger than a few hundreds of nanometers". How is that statement relevant to chiral OIHP films grown in nanopore substrates with pore sizes less than ~100nm? 9. Page 9 and Page 12 contains a statement on line 303-306 which reads, "The CPPL spectra give useful information on the ground state of chiral 2D OIHPs, whereas CD spectroscopy can provide information regarding the electronic structure of the excited state of materials". This statement is oversimplified and is actually confusing/misleading. The ground state of chiral OIHPs (or any system) has no excitons. Both CD and CPPL give information on transitions that involve the ground state and various excited states. It is true that CD (and absorption spectroscopy generally) can access information about transitions involving higher energy states than PL spectroscopies can access generally; but PL spectra such as CPPL are heavily influence by spin and energy relaxation processes and are therefore often difficult to interpret meaningfully.
Reviewer #4 (Remarks to the Author): In the article "Multi-Polar Interaction: The Origin of Chiroptical Activity in Chiral 2D Perovskites" the authors investigated 2D hybrid organic-inorganic perovskites having chiro-optical activity. In particular they focus on MBA2PbI4(1-x)Br4x systems. The study involves both experimental characterization and theoretical explanations, mainly based on Density Functional Theory (DFT) calculations.
Starting from experimental characterization of the optical activity due to the chirality of the structure, they proposed a theoretical interpretation in terms of an indirect interaction (there is no chemical bonding) between organic spacers (chiral molecular cations) and the framework.
We discussions seem appropriate and supported both from experiments and calculations.
I believe that the article will be interesting for the large community working on hybrid perovskites, and certainly, 2D Chiral HIOPs are an hot topic in material science. Therefore, I recommend publication in Nat. Comm. I have a minor comment: Formula (3), line 239, should not be called quadruple product. A quadruple product involves 4 vectors, and it can be either scalar or vector quadruple product. In this case, V12 is simply a scalar quantity (Davydov splitting), which acts as a scale factor. Therefore, I would refer to a triple product (the quantity in square brackets), scaled by V12.

Author's Response:
We agree with the reviewer that the one of the important mainstream topics for chiral photonic studies are bio responsive imaging [R1] and chiral biosensing [R2]. Therefore, as the reviewer commented, the statement related to the biosensing and potential application of chiral perovskite have been added. We have also cited some references that reviewer recommended.
We thank the reviewer for careful comment. Chiralplasmonics and their potential for point-of-care biosensing applications.

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(in Page 2, Introduction) Chiral photonics based on chiroptical phenomena have attracted tremendous scientific interest in a wide variety of fields, such as opto-spintronics, 1,2 optical information processing, 3 biological science, 4 chiral biosensing, 5,6 and quantum computing. 7 Author's Response: We appreciate the reviewer for important comment regarding the conceptual novelty of our strategy based on strain-engineering for enhancing the chiroptical activity. Although we observed the lattice distortion of chiral 2D perovskites induced by nanoconfined growth in AAO templates (XRD patterns in Fig. 1d and calculated micro-strain data obtained by modified Williamson-Hall methods in Fig. 2b), we elucidate that the resulting octahedral tilting and lattice distortion in achiral inorganic framework can be amplified by the asymmetric hydrogen bonding between the achiral inorganic framework and chiral organic cations, which is the fundamental origin of amplified chiroptical activity in nanoconfined chiral 2D perovskites. Indeed, we focused on the conformational stacking change of benzene rings in chiral methylbenzylamine (MBA) cations due to the weak bonding nature of noncovalent ππ interactions. Because the stacking conformation (e.g., distance and angles between the benzene rings) of benzene ring in MBA organic spacer cations varies, the AAO templated chiral 2D OIHPs tend to exhibit a zigzag tendency of micro-strain magnitude rather than a linear dependency on the pore size as shown in previously reported 3D perovskites [R3, R4].
In addition, based on the first-principles density functional theory (DFT) calculation results, we concluded that the variation of hydrogen bonding interaction between the achiral inorganic framework and chiral organic molecules (not the structural variation) is likely a key origin of the amplified chiroptical activity of chiral 2D perovskites.
In the previous report that reviewer commented [R5], the chiroptical activity of Co3O4 nanoparticles (NPs) is attributed to the lattice distortion on surface of NPs caused by molecular imprinting (i.e., attaching chiral surface ligand such as cysteine). Although the chirality transfer phenomena are propagating from chiral ligand to the lattice of the inorganic NPs core, the chirality transfer mechanism is based on the spatially rearrangement of atoms in achiral system (not originated from the inherent chiral crystal structure). On the other hand, the incorporation of the chiral MBA molecules (not adsorption on the surface) into the lattice results in an inherent chiral crystal structure (chiral space group of P212121 for MBA2PbI4).
Therefore, the origin of chiroptical phenomena in these two systems are based on the completely different chirality transfer mechanisms (e.g., surface chiral ligand induced atomic rearrangement versus inherent chiral crystal structure formation). In the case of semiconductor nanowires (NWs) in previous report (Nano Lett. 15, 1710-1715(2015), the chirality transfer mechanism is based on the chiral lattice distortion, which is similar to the above-mentioned chirality transfer mechanism in NPs (spatial rearrangement of atoms).
Consequently, we assert that our results are completely different from the previous studies that reviewer mentioned. Furthermore, we would like to emphasize that our discovery and understanding of chiroptical activity in chiral 2D perovskites are unprecedented for the following reasons (vide infra):

(a) New strategy for improving chiroptical activity in chiral 2D perovskites
Although the attractive spin-related and chiroptical properties of chiral 2D perovskites have led to a recent research interest, the numerous studies have been limited to only suggest new composition of chiral perovskites (e.g., substitution of chiral organic molecules, halide composition engineering, and dimension control). On the contrary, to the best our knowledge, this is the first report on enhancing the chiroptical activity of chiral 2D perovskite without any compositional change. Even though the same precursor solutions were utilized (i.e., the same ratio between the chiral molecules to inorganic lead halide precursor; the same dimension of perovskites, and the same halide composition), nanoconfined chiral 2D perovskites revealed exceptionally enhanced chiroptical activity (circular dichroism (CD) and circularly polarized photoluminescence (CPPL)) compared to their planar counterparts.

(b) Elucidating the origin of chiroptical activity other than crystal structure
Due to the structural flexibility of 2D perovskites, the chiroptical activities in chiral perovskite are usually interpreted as the chirality transfer mechanism based on inherent chiral crystal structure. Although the crystal structure-property relationship provides a straightforward explanation of chirality transfer phenomena, significantly enhanced chiropitcal activity in our experimental results cannot be fully explained by the prevailing chirality transfer mechanism. Therefore, we suspect that the huge enhancement of chiroptical activity might originate from the other underestimated mechanism; not from crystal structure-chiroptical property relationship. Very recently, Mitzi et al. discovered that the induced CD of chiral 2D OIHPs do not always accompany structural chirality transfer from organic to inorganic layers as manifested by centrosymmetric breaking in inorganic frameworks [R6]. Their experimental results and theoretical calculation are consistent with our findings. For the first time, we observed that the hydrogen bonding interaction between chiral molecular spacers and the inorganic framework can be modified by imposing micro-strain into the lattice of 2D perovskite. Combining experimental results and DFT calculation, we verified that the chirality transfer mechanism based on the electronic interaction plays a key role in promoting the chiroptical activity of chiral perovskites. p.13, Figure 4. The CPPL data are very interesting and complementary. However, both CD and potentially CPPL spectra of AAO templated MBA2PbI can depend on the incident angle. It will likely to change the spectra and thus the small changes in FE peaks can be ascribed to the change in the incident angle.

Author's Response:
We appreciate the reviewer for constructive comments regarding the change of spectra as a function of incident light angle. We understood that reviewer asks us to exclude the effect of incident angle on chiroptical activities associated with free exciton (FE) transition that arises from the experiment condition. However, when we conducted the chiroptical analysis (both CD and CPPL), the measurement condition (including incident light angle as well as relative humidity and temperature) were carefully controlled. Regardless of the substrate conditions, all the CD and CPPL spectra ( Fig. 1 and Fig. 4, respectively) for the chiral 2D perovskite were obtained under the same measurement conditions. Therefore, we assume that the different chiroptical behavior (i.e., different anisotropy factor of photoluminescence of 4.7 × 10 -3 for planar and 6.48 × 10 -2 for AAO template in Fig.4c Fig. S15a). As 8 shown in Fig. S15b, despite of the huge difference of incident angle (between 45° and 60°), the CPPL intensity exhibit only negligible difference in FE transition, implying that the carrier and recombination dynamics is independent on the incident angle of excitation laser. Therefore, we assume that the different chiroptical behavior (i.e., different anisotropy factor of photoluminescence of 4.7 × 10 -3 for planar and 6.48 × 10 -2 for AAO template in Fig.4c and d, respectively) is attributed to different charge carrier dynamics induced by nanoconfined growth rather than the incident angle variation of excitation laser.

<Reviewer 2>
In this manuscript, Ma and coauthors have investigated the chirality transfer mechanism in chiral perovskites. They concluded that the multi-polar interaction between chiral molecular spacers and the inorganic framework plays a key role in promoting the chiroptical activity of chiral perovskites via the in-depth investigation of chiroptical phenomena-based oscillator coupling theory and theoretical calculations. Chiral perovskites would find promising applications in spintronic-and polarization-based optoelectronic devices and understanding the chirality transfer mechanism would be essential for the material design and device construction. Therefore, this study is important to the chiral perovskite community.
Nevertheless, the conclusions cannot fully supported by the provided experimental evidences.
I cannot recommend its publication at the current form.

Remark:
We would like to gratefully thank the reviewer for reviewing and evaluating our work. We believe that the reviewer's comments highly improve the quality of our manuscript. Our response to the reviewer's comments can be found below.

Comment 1:
The detailed material characterizations for the strain-imposed chiral 2D perovskites are missing. Are those strain-imposed chiral 2D perovskites in the pores of AAO single crystals?
What is the size distribution of the as-grown 2D perovskites on AAO substrates? The authors also need to provide the morphology information on the as-grown samples.

Author's Response:
We appreciate the reviewer's critical comment on the material characterizations for the confined grown 2D perovskites. The additional crystallographic and morphological analyses have been conducted to characterize the crystalline properties. First, to investigate whether the strain-imposed chiral 2D perovskites are single crystal, high-resolution transmission electron microscope (HRTEM) was applied to analyze the structure and morphology of the crystalline grains. Since the overlayer grown on the top of the AAO template will disturb our experimental subject (i.e., nanoconfined chiral 2D perovskite inside the pore of AAO template), it is necessary to prevent the formation of such an overlayer by using a precursor solution with low concentration. Due to the low precursor concentration, the cross-sectional HRTEM image in Fig. R2 reveals that the pores of AAO template are partially filled with conjoined chiral 2D perovskite nanocrystals. There are no grain boundaries in conjoined chiral 2D perovskites, confirming that strain-imposed chiral 2D perovskites grew as a single crystal, which is also observed in our previous report [R9, R10]. Although there is large empty space in the pores of AAO templates, the horizontal growth of chiral 2D perovskite (parallel to substrate) is sufficient to fill the pores in the horizontal direction. This implies that the growth of chiral 2D perovskite along the horizontal direction is hampered by the pore wall, inducing the microstrain into the lattice along the c-axis (nano-confined growth direction) which is parallel to the preferred orientation of chiral 2D perovskite ((002l) plane). These results, which are consistent with our findings of the induced micro-strain direction in the X-ray diffraction (XRD) patterns ( Fig. 1d) and modified Williamson-Hall method (Fig. 2b), can also justify our interpretation on DFT calculations that focus on the shrinkage range in the out-of-plane direction (e.g., negative uniaxial strain; i.e., yellow region in Fig. 3c in our manuscript).
Since the interaction direction between the pore wall of AAO templates and chiral 2D perovskites is parallel to substrate, the average lateral size of single crystal (parallel to AAO substrates), which can determine the degree of micro-strain along the c-axis, is the main concern of our investigation. As the lateral size of single crystal is limited by the pore size of AAO templates, we can calculate the average horizontal size of single crystal by analyzing the pore size distribution. By using ImageJ software (Wayne Rasband, National Institutes of Health, USA), we estimated the size distribution for three different AAO templates as 66.4 ± 1.3, 100.3 ± 3.9, and 112.7 ± 5.2 nm. The image analysis confirms that the pore size of AAO templates exhibits a very narrow distribution. This narrow distribution of pore size results in coherent distribution of average horizontal sizes of nanoconfined chiral 2D perovskites in AAO templates, ensuring the reliable experimental results obtained from the micro-strain analysis. We thank the reviewer for improving the reliability and quality of our work.

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(in Page 4-5) ••• The same precursor solutions were deposited on a glass substrate (hereafter denoted as planar) and AAO templates with different pore sizes, followed by spin coating and a subsequent annealing process. It is worth to note that the overlayer grown on top of the AAO template will disturb our experimental subject (i.e., nanoconfined chiral 2D OIHPs in the pore of AAO template: imposing the micro-strain into the lattice of chiral 2D OIHPs). Therefore, it is necessary to prevent the formation of such an overlayer by using a precursor solution with low concentration. As shown in Supplementary Fig. S2, nanoconfined chiral 2D OIHPs in AAO templates grew as a single crystal without grain boundary, which is consistent with our observation in previous report. 31 The horizontal growth (parallel to the substrate) of single crystalline chiral 2D OIHPs is effectively hampered by the pore walls of AAO templates as expected.

(in Page 13)
••• In addition, the The observed peak shift in the iodide-determinant phase (toward higher 2θ degree) suggests that confined growth induces lattice shrinkage along the c-axis. In addition, the horizontal growth of chiral 2D OIHPs is effectively inhibited by the pore wall (parallel to substrate) (as shown in Fig.S2 Supplementary), the direction of imposed micro-strain is outof-plane direction (i.e., parallel to pore wall). Therefore, we need to focus on the shrinkage range in the out-of-plane direction (i.e., negative uniaxial strain and positive biaxial strain; yellow region in Fig. 3c and d) to properly interpret our DFT calculations. As the lateral size of single crystal is limited by the pore size of AAO templates, we can calculate the average horizontal size of single crystal by analyzing the pore size distribution.
By using ImageJ software (Wayne Rasband, National Institutes of Health, USA), we estimated the size distribution for three different AAO templates as 66.4 ± 1.3, 100.3 ± 3.9, and 112.7 ± 5.2 nm ( Supplementary Fig. S2). The image analysis confirms that the pore size of AAO templates (i.e., lateral size of single crystalline chiral 2D OIHPs) exhibits a very narrow distribution. 13

Comment 2:
If the as-grown chiral 2D perovskite samples are not single crystals, how the results the authors obtained will change? How the non-uniform size influences the conclusions the authors obtained?
Author's Response: We appreciate the reviewer's critical comment on the statistical analysis of crystalline size of chiral 2D OIHPs with respect to the reliability of our experimental finding. As we explained before (in our Response to Comment 1 for Reviewer 2), the pore size in AAO templates as well as lateral size of single crystal chiral 2D OIHPs exhibits very narrow size distribution. In addition, the micro-strain values by the modified Williamson-Hall method were statistically calculated from the several repetitions of XRD measurement (average calculated strain values and standard deviation were presented in Fig. 2b). Therefore, we believe that the concern resulted from the size distribution or non-uniform size can be excluded from our conclusion.
The authors claimed that there is strain in the samples grown on AAO substrates. Can the authors directly provide the experimental evidences and estimate the strain from them? For example, PL spectrum would change under external strain.

Author's Response:
We appreciate the constructive comments raised by the reviewer. In previous literature, the spectral peak position of PL could shift to lower energy as pressure increases [R11].
Furthermore, we observed the lattice shrinkage along the c-axis in nanoconfined chiral 2D OIHPs, which can lead to the bandgap narrowing. Therefore, as the reviewer suggested, we performed photoluminescence (PL) measurement with the chiral 2D OIHPs grown in different substrate conditions (e.g., planar, 66 nm-, 100 nm-, and 112 nm-pore sized AAO templates) to provide direct experimental evidence regarding imposed strain in chiral 2D OIHPs. As shown in Fig. R3, the PL spectra of chiral 2D OIHPs reveal completely different emission behavior depending upon the grown substrates. The chiral 2D OIHPs grown in AAO templates (regardless of pore sizes) exhibit significantly enhanced PL intensity than planar substrate condition. It is attributed to the reduced defect density and suppressed trap states due to the well-controlled crystallization during the confined growth.
To correlate the spectral peak shift of PL according to the induced micro-strain in the lattice of chiral 2D OIHPs, we carefully calculated the energy of PL emission from each substrate condition. The PL emission energy as a function of AAO template pore sizes was plotted in Fig. R4a. For clear comparison, the plot of calculated micro-strain values versus pore size ( Fig. 2b in our manuscript) is also presented as Fig. R4b. Interestingly, the plot of PL emission energy also exhibits zigzag tendency as a function of the template pore size, which is similar to the calculated micro-strain plot. It is worth noting that the direction of y-axis in both plots (i.e., PL emission energy in Fig. R4a and calculated micro-strain in Fig. R4b   In previous literature, it is well known that the spectral peak position of photoluminescence (PL) could shift with varying the degree of micro-strain. 42 Therefore, to confirm the existence of the micro-strain in the lattice of chiral 2D OIHPs induced by the AAO templates, we conducted PL measurement with the chiral 2D OIHPs grown in different substrate conditions (e.g., planar, 66 nm-, 100 nm-, and 112 nm-pore sized AAO templates).
As shown in Supplementary Fig. S8a, the PL spectra of chiral 2D OIHPs reveal completely different emission behavior depending upon the grown substrate. The chiral 2D OIHPs grown in AAO templates (regardless of pore sizes) exhibit significantly enhanced PL intensity than planar substrate condition due to the reduced defect density and suppressed trap states. These results indicate that, as previously reported, the confined growth in AAO templates efficiently controls the crystallization kinetic of OIHPs, resulting in a high-quality single crystal in AAO templates. 31,38 Furthermore, to correlate the spectral peak shift of PL according to the induced micro-strain in the lattice of chiral 2D OIHPs, we carefully calculated the energy of PL emission obtained from each substrate condition. The PL emission energy as a function of AAO template pore sizes was plotted in Supplementary Fig. S8b. Interestingly, the plot of PL emission energy also exhibits zigzag tendency as a function of the template pore size, which is similar to the calculated micro-strain plot. This implies that the PL emission shift is originated from the imposed micro-strain in the lattice of chiral 2D OIHPs. Such a coincident tendency (i.e., similar zigzag tendency in both PL emission energy and calculated micro-strain) reconfirmed the existence of the micro-strain imposed by AAO templates.

(in Page 12)
••• Interestingly, in the entire composition range (from x = 0.325 to x = 0.400), the corresponding variation in Davydov splitting also exhibited a zigzag tendency, which is similar to the calculated micro-strain results (Fig. 2b) and PL emission shift ( Supplementary Fig. S8b).
Such a coincident tendency (i.e., similar zigzag tendency in calculated micro-strain, PL emission shift as well as Davydov splitting) can support that unprecedentedly observed chiroptical conversion behavior in AAO templated chiral 2D OIHPs results from facilitated chirality transfer phenomena from chiral organic cations (MBA + ) to achiral inorganic framework (lead halide) induced by the micro-strain. nm. b, Corresponding the PL emission peak energy plot obtained from the steady-state PL spectra as a function of AAO template pore sizes.
In addition to strain, there might be other factors that alter the chiroptical behaviors such as quantum confinement effect itself. How can the authors exclude other possibilities?
Author's Response: We thank the reviewer for the important comment on the origin of the unprecedent chiroptical activity in chiral 2D OIHPs. We understood that reviewer asks us to consider the other possible origin of the chiroptical behavior that could arise from the confined growth in AAO templates, such as quantum confinement effect. As the reviewer commented, strong quantum confinement effect might cause bandgap widening and change of electronic structure as well as carrier transport dynamics. However, the quantum confinement effect can be observed when the size of particles is less than 10 nm (e.g., quantum dots (QDs) or nanoparticles (NPs) whose size is comparable to the wavelength of electron. Even the smallest single crystal size of chiral 2D OIHPs is about 60 nm as defined by the pore size of AAO templates, which far exceeds the electron wavelength. Furthermore, our DFT calculation results suggested that the interaction between the inorganic perovskites slabs and the chiral organic spacer was enhanced by the micro-strain induced due to the lattice shrinkage along the c-axis. It is well known that strong interaction between the inorganic frameworks and the chiral organic spacer cation weakens the quantum confinement effects in 2D OIHPs.[R12, R13] Therefore, we can exclude the quantum confinement effect on the chiroptical activity of chiral 2D OIHPs.  15170-15175 (2015).

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(in Page 6) ••• different chromophores are located nearby in space and have a proper chiral mutual orientation. 33,34 In order to eliminate the interference induced by the optical anisotropic properties of AAO templates, CD measurement was also carefully investigated with empty AAO substrates with various pore sizes ( Supplementary Fig. S3). Although the CD spectra of bare AAO templates exhibit huge CD signal (nearly 100 mdeg) due to the overestimated scattering contribution of transmitted CD measurement, which is common in nanostructured materials with definite spatial orientations, 35 the empty AAO templates show no CD signal in the wavelength range above 350 nm. This implies that the effect of the optical anisotropy from the bare AAO templates can be completely excluded. Therefore, the observed sign conversion and spectral shape change of the Cotton effect imply that spatial confinement by AAO templates might induce the coupling modulation between the chiral chromophores, resulting in the reconstruction of the chiroptical band structure.  The CD spectra of perovskite grown on planar substrates exhibit unisignated CD signal at the first excitonic transition. Can the author explain the reason for uncommon behavior (not bisignated Cotton effect but unisignated CD)?

Author's Response:
We thank the reviewer for the comment. However, it is not uncommon behavior to exhibit unisignated CD signal at the first excitonic transition in chiral OIHPs.[R15,R16,R17] In chiral OIHPs, the different absorption between left-handed circularly polarized light (LCP) and righthanded circularly polarized light (RCP) occurs when the degeneracy of electronic state is slightly lifted by the perturbation due to the chirality of the chiral organic molecules; energy state with one spin can go relatively higher energy compared to the other spin state. In this case, the intensity of the CD spectra can be estimated by rotational strength, which is directly proportional to the scalar product as expressed by equation (1) where Rab describes the rotational strength related to the transition from state a to b, μab, mab,

Comment 7:
The authors are suggested to provide the results of rac-MBA samples grown on both planar and AAO substrate for comparisons.

Author's Response:
Thank you for important comment. We understood that the reviewer ask us to rule out the possible effect of AAO substrate on the chiroptical activity of 2D OIHPs by comparing optical activity of R-and S-configurations with that of racemic compound. Therefore, during the revision work, we additionally conducted CD measurement and XRD analysis with rac- MBA2PbBrxI4-x (x=0.325) to clearly confirm the effect of nanoconfined growth on the chiroptical activity of chiral 2D OIHPs. As shown in Fig. R7, the CD spectra of racemic samples do not exhibit any notable chiroptical response in the range of 425-525 nm regardless of the grown substrate conditions (e.g., planar, 66 nm-, 100 nm-, 112 nm-pore sized AAO templates). Considering the aforementioned CD results of bare AAO substrates (in our Response to Comment 5 for Reviewer 2), we verify that unprecedent chiroptical phenomena of nanoconfined chiral 2D OIHPS in AAO substrates is not due to the optical anisotropy of the AAO substrate itself; rather, the amplified CD signal, sign conversion of Cotton effect, and huge difference in CPPL intensity are originated from the micro-strain induced by nanoconfined growth in AAO templates. Furthermore, the XRD spectra of racemic samples also confirmed that the nanoconfined growth in AAO templates do not affect the crystallization process without impairing the preferred orientation and quality of chiral 2D OIHPs (Fig. R8).

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(in Page 10-11) ••• Interestingly, the abnormal chiroptical behavior (i.e., amplified CD signal, sign conversion, and spectra shape change in the Cotton effect) was also observed for the chiral 2D OIHPs thin films with all the compositions (from x = 0.350 to 0.400 as well as x = 0.325) ( Supplementary   Fig. S6). We also conducted the CD measurement and XRD analysis with racemic MBA2PbBrxI4-x (x=0.325) to clearly confirm the effect of nanoconfined growth on the chiroptical activity of chiral 2D OIHPs. As shown in Fig. S10 (Supplementary), the CD spectra of racemic compound do not exhibit any notable chiroptical response in the range of 425-525 nm regardless of the grown substrate conditions (e.g., planar, 66 nm-, 100 nm-, 112 nm-pore sized AAO templates), implying that the abnormal chiroptical behavior in chiral 2D OIHPs is not due to the optical anisotropy of the AAO substrate itself, but rather resulted from the promoted chirality transfer from organic spacer cations to achiral inorganic frameworks. The XRD spectra of racemic samples with different AAO templates condition also show no noticeable difference, suggesting that the nanoconfined growth in AAO templates do not influence on the crystallization process without impairing the preferred orientation and quality of chiral 2D OIHPs ( Supplementary Fig. S11). These observations imply that the chirality transfer could be effectively promoted by nanoconfined growth in AAO templates, resulting in the modulation of chiroptical activity in chiral 2D OIHPs even at higher bromide composition.

Author's Response:
We thank the reviewer for the comment. It is expected that Rashba effect or Rashba-Dresselhaus effects can occur under an external magnetic field even in the achiral OIHPs. As the reviewer commented, similar to the external magnetic field applied condition, excitation by the circularly polarized light also can lift the degeneracy of spin state due to the large spinorbit coupling (SOC) of OIHPs. If the huge difference PL emission intensity between the RCP and LCP in the CPPL measurement is originated from the Rashba effect and the induced spin degeneracy rather than due to the intrinsic chirality transfer phenomena, the different emission rates of RCP and LCP should be also detected in racemic compound under the same measurement condition. Therefore, to clarify the origin of different emission rate of RCP and LCP, the CPPL measurement was also performed in the same manner (i.e., using circularly polarized laser as an excitation source) for racemic compounds grown on AAO templates with pore size of 100 nm.
As shown in Fig

(in Page 15-16)
To exclude the effect of Rashba splitting on CPPL spectra, which might arise from the experimental procedure (because the excitation by the circularly polarized light can lift the degeneracy of spin state due to the large spin-orbit coupling (SOC) of OIHPs), and to clarify the origin of different emission rate of RCP and LCP, the CPPL measurement was also performed in the same manner (using circular polarized light as a excitation source) for racemic compounds grown on AAO templates with pore size of 100 nm. As shown in Fig. S14 (Supplementary), the racemic compounds grown in AAO templates do not show any different emission behavior between the RCP and LCP. The CPPL spectra of racemic compounds grown on AAO templates suggested that the Rashba effect and coherent lifting of the spin degeneracy by the circularly polarized light did not occur in the absence of chirality transfer phenomena (i.e., in the absence of chiral organic molecules). This implies that enhanced asymmetric factor 30 of CPPL (gCPPL) in chiral 2D OIHPs results from the facilitated chirality transfer phenomena rather than Rashba effect itself (by the excitation using circular polarized light). Very recently, Mitzi group found that the Rashba-Dresselhaus spin-splitting is a consequence of the chirality transfer phenomena. 44 Based on their findings and experimental results, the other effects such as Rashba effect or Rashba-Dresselhaus spin-splitting (whether it occurs or not), which might contribute to the measured CPPL, cannot be explained separately. Rather, such effects should be included as a consequence of the chirality transfer phenomena facilitated by nanoconfined growth in AAO templates. Some important recent works on chiral 2D perovskites are missing. The authors are suggested to introduce and cite them in the revised manuscript.

Author's Response:
We thank the reviewer for the comment. We have added the references of important recent works on chiral 2D perovskites in our manuscript.

Revision made (colored in blue):
(

<Reviewer 3>
I was excited by the title and abstract of this manuscript. The authors attempt to address a difficult and important problem (the origin/mechanism or chiro-optical phenomena in chiral metal halide systems) and the abstract promises analysis in terms of a very interesting new idea, namely, multipolar interactions involving the chiral cations in these systems. Not mentioned in the abstract was the technique used of growth in nano-pore substrates; this is a very clever idea. However after reading the work I find that the claims made are not well supported by the work, it seems very preliminary. In addition, the manuscript is missing some essential information and the presentation needs to be substantially improved.
Here I summarize what I see as the major technical issues; further below I will make comments on the presentation of the manuscript and list other minor technical issues I noted while reading the manuscript.

Remark:
We would like to thank the reviewer for evaluating our work as an interesting new idea to clarify the origin/mechanism of chiroptical activities in metal halide systems. Our response to the reviewer's comments can be found below.

Comment 1:
Analysis of micro-strain of films grown on AAO nanopore substrates. It is difficult to believe that this is a correct analysis. If I understand correctly what the 0 nm pore size means, then this sample comprises a planar film. Given the weak non-covalent interaction between layers it is highly unlikely that these films are epitaxial so the -6% strain of this "0 nm pore" sample is quite a mystery. Indeed, there is no correlation between the derived micro-strain and the nano-pore size (see plot in Fig2b). The Authors' own description on line 167, is that the nano-pore size is of "unexpected irrelevance".
c. Yet the interpretation of the XRD pattern in terms of the micro-strain is a foundational element of the author's interpretation and claims.

Author's Response:
We appreciate the reviewer's comment. We understood that the reviewer asks us to provide more detail information of the micro-strain analysis and to demonstrate the validity of experimental results from the modified Williamson-Hall methods. First of all, as the reviewer assumed, the mention "pore size of 0 nm" is correct to mean "there are no pores". The sample with pore size of 0 nm represents thin films of chiral 2D OIHPs grown on planar substrates without porous template. In order to eliminate the possible confusion and misunderstanding, we have added the definition describing the chiral 2D OIHPs grown on "substrate with pore size of 0 nm".
For the chiral 2D OIHPs grown on substrate with pore size of 0 nm (i.e., planar substrate), we observed the presence of -6% micro-strain in the lattice of OIHPs, even though the thin films were grown freely without spatial confinement. Reviewer pointed out, "How then is it possible that the micro-strain shown for the 0 nm pore size in Fig 2b is -6%?" However, it is not uncommon that the local lattice strain exists in OIHPs thin films grown on planar substrate condition due to the lattice mismatch, atomic size misfit, mismatch of thermal expansion, or lattice defects.[R19, R20, R21] Since we have calculated the degree of microstrain by the comparison with the strain-free single crystalline data (i.e., MBA2PbI4 single crystal as standard material), the obtained value of -6% micro-strain from the thin films of chiral 2D OIHPs grown in planar substrate is reasonable. We are sorry that the experimental procedure of micro-strain analysis in Supplementary did not provide sufficient information on how the micro-strain was calculated. Therefore, we have added and modified the experimental procedure to include the corresponding calculation process and single crystalline data in the revised manuscript.
Furthermore, as the reviewer pointed out, we mentioned the calculated micro-strain values exhibit "unexpected irrelevance" with the pore size of AAO templates in our manuscripts. However, when we use the term of "unexpected irrelevance", it was not intended that there is no correlation between the derived micro-strain and the nano-pore size. Since the calculated micro-strain values are inversely proportional to the pore size of AAO templates in our previous reports regarding 3D OIHPs, the expression "unexpected irrelevance" rather just comprehensively implies unexpected behavior (not inversely proportional to the pore size of AAO templates). For clarification, the expression "unexpected irrelevance" has been replaced with "unexpected non-linear behavior" in our revised manuscript.
To elucidate the relationship between the pore size and resulting micro-strain, the calculation of the external stress exerted by the pore wall at each spatial confinement condition as a function of pore sizes must be preceded. However, as the optimal π-π stacking structure of 2D OIHPs varies with the given spatial restriction condition, it is hard to directly calculate the magnitude of external stress exerted by the pore wall. Therefore, to provide direct experimental evidence of imposed strain induced by pore wall and to correlate micro-strain values depending upon the pore size of AAO templates, we additionally conducted the PL measurement of chiral 2D OIHPs grown on different pore-sized AAO templates (please see our Response to Comment 3 for Reviewer 2). Remarkably, the plot of PL emission energy also exhibits zigzag tendency as a function of the template pore sizes (as shown in Fig. R4), which is similar to that of the calculated micro-strain plot. Such a coincident behavior implies that the shift of PL emission not only provides the direct evidence of micro-strain imposed by AAO templates but also demonstrates the validity of the modified Williamson-Hall methods.
Consequently, the correlation between the deviation of chiroptical activities and the resulting micro-strain induced by the nanoconfined growth, which is a core objective of this paper, was well supported by experimental results and strain analysis.

Revision made (colored in blue):
Description of detail experimental procedure of strain-analysis and definition describing the chiral 2D OIHPs grown on planar substrate (with 0 nm pore size) has been added.
(in page 4) ••• The same precursor solutions were deposited on a glass substrate (hereafter denoted as planar or substrate with 0 nm pore size) and AAO templates with different pore sizes (in page 7) ••• For the accurate assessment of the micro-strain imposed by AAO templates, the XRD patterns for chiral 2D OIHPs with various halide composition (e.g., MBA2PbI4 as well as MBA2PbI4 (1- (in page 9) ••• the magnitude of micro-strain rather revealed a zigzag tendency, as shown in Fig. 2b, than a linear dependency on the pore size. It is worth to note that the presence of -6% micro-strain in the lattice of OIHPs was observed in 0 nm pore size condition, even though the thin films were freely grown on planar substrate without spatial confinement. However, it is not uncommon that the local lattice strain exists in OIHPs thin films grown on planar substrate due to the lattice mismatch, atomic size misfit, mismatch of thermal expansion, or lattice defects. 39,40,41 As mentioned above, we have calculated the degree of micro-strain by the comparison with the strain-free single crystalline data (i.e., MBA2PbI4 single crystal as standard material), the obtained value of -6% micro-strain from the thin films of chiral 2D OIHPs grown in planar substrate is reasonable. For clarification, the expression "unexpected irrelevance" has been replaced with "unexpected non-linear behavior" or with appropriate term in context.

(in page 9)
The unexpected irrelevance unexpected non-linear behavior of calculated micro-strain values for AAO templated chiral 2D OIHPs as a function of pore size can be possibly understood by the •••

Comment 2:
CD and dissymmetry spectra are shown in Fig 1 and in the SI, and details of the deconvolution procedure they use to assign transitions are described in the SI (Suppl Note 4). However, no absorption or extinction spectra are shown. It is problematic to evaluate statements about the nature of the spectral features in the CD spectra and how they are de-convolved and assigned without seeing these spectra.

Author's Response:
We thank the reviewer for the critical comment on the CD and dissymmetry spectra together with deconvolution procedure to assign the transition. As the reviewer commented, to assign the signal in the CD spectra to different excitonic transition level, the absorption or extinction spectra should be presented. In addition, the chiroptical activity of chiral 2D OIHPs due to the chirality transfer process occurs around 475 nm, which is associated with the transition in inorganic framework.
Therefore, CD spectrum fitting procedure was mainly focused on the first extinction band edge range. As a result, the intense CD signal at longer wavelength can be assigned to the first excitonic transition in absorption spectra (red dot line in absorption spectra), which is consistent with the previous report.
[R22] We have added the figure in Supplementary to provide corresponding extinction spectra. To elucidate how the micro-strain (nanoconfined growth in AAO templates) influences the degree of the intra-octahedron distortion (degree of the chirality transfer), we have also calculated the hydrogen bonding length between NH3 + groups of chiral organic spacer and nearest iodine atom of inorganic framework. It is worth noting that there are four different distinguishable hydrogen bondings in the unit cell of MBA2PbI4 (denoted as HBtop1, HBtop2, HBbot1, and HBbot2). Interestingly, as shown in Fig. R12, the asymmetric nature of hydrogen bonding (variance and difference between the hydrogen bonding lengths) was amplified when the lattice shrinkage occurs along the c-axis (region of negative uniaxial strain and positive biaxial strain). The DFT calculation results support that the asymmetric behavior of hydrogen bonding between the chiral organic molecules and inorganic framework can be amplified depending on the degree of micro-strain, which can effectively promote the chirality transfer process and larger chiral distortion in inorganic framework.
Based on the above discussion and theoretical calculation results, we suggest that the origin of unprecedented chiroptical activities in nanoconfined chiral 2D OIHPs can be explained by the efficient chirality transfer promoted by asymmetric hydrogen-bonding interaction between the chiral spacer and inorganic frameworks. We guarantee that our assertation is fully supported by the related calculation results. Addition of Fig. R11 and R12 and related calculation results into the revised manuscript will clarify the relationship between the micro-strain and induced chiroptical activities in chiral 2D OIHPs, while satisfying the reviewer's concern. We gratefully thank the reviewer for helpful comments which significantly improves the quality of our manuscript.
In addition, we believed that the comment of "nano-confined MBAPbX4 is responsible for the emergence of bi-signate CD spectra, as claimed here, why are bi-signate CD spectra

Revision made (colored in blue):
(in page 11) ••• while e i ⃗ is the corresponding unit vector. It is worth to noting that the abnormal chiroptical behaviors (i.e., amplified CD signal, sign conversion, and spectra shape change in the Cotton effect) observed in AAO templated chiral 2D OIHPs occur at ~ 475 nm (near the band edge extinction of chiral 2D OIHPs), which is far from the wavelength region where the exciton transition of chiral MBA + cations occurs (~ 260 nm). Therefore, the CD signal of chiral 2D OIHPs in Fig. 1a should be interpreted as a result of excitonic transition behavior in the lead halide inorganic framework where the chirality was induced by the chirality transfer phenomena. Since the MBA + spacer cations (MBA1 and MBA2) are the only possible candidates for generating the CD signal (because the transition dipole moment of two MBA + cations cannot be located in the coplanar due to their inherent chirality), it is logical to conclude that the conformational π-π stacking variation of chiral organic spacer MBA + cations is the origin of abnormal chiroptical behaviors (i.e., amplified CD signal, sign conversion, and spectra shape change in the Cotton effect) observed in AAO templated chiral 2D OIHPs. It is logical to conclude that the efficiency (or degree) of the chirality transfer can greatly vary depending upon the imposed micro-strain. In this manner, we propose the stepwise chirality transfer mechanism to interpret the unprecedent chiroptical activity of chiral 2D OIHPs in AAO templates: i) conformational stacking order of chiral organic cations (i.e., angle and length between the MBA1 and MBA2) changes due to the imposed micro-strain, ii) the electronic interaction between the chiral organic molecules and achiral inorganic framework was enhanced (or reduced), iii) the chirality transfer from the chiral organic cation to inorganic framework was promoted (or suppressed).

(in page 14)
To verify the relationship between the imposed micro-strain and the efficiency of chirality transfer in chiral 2D OIHPs π-π stacking conformation variation and the electronic state of To support our scenario of facilitated chirality transfer phenomena by imposed microstrain, we analyzed structural properties of MBA2PbI4 as a function of micro-strain. It is worth mentioning that MBA2PbI4(1-x)Br4x thin films exhibit sharp XRD diffraction peaks assignable to the (002l) planes regardless of the growing substrates and bromide composition, indicating the highly preferred orientation along the c-axis ( Fig. 1d and Supplementary Fig. S13). The observed peak shift in the iodide-determinant phase (toward higher 2θ degree) suggests that confined growth induces lattice shrinkage along the c-axis. In addition, the horizontal growth of chiral 2D OIHPs is effectively inhibited by the pore wall (parallel to substrate) (as shown in Fig.S2 Supplementary), the direction of imposed micro-strain is out-of-plane direction (i.e., parallel to pore wall). Consequently, we need to focus on the shrinkage range in the out-ofplane direction (i.e., negative uniaxial strain and positive biaxial strain; yellow region in Fig.   3b and c) to properly interpret our DFT calculations. To correlate the imposed micro-strain and the degree of chirality transfer, the specific structural parameters such as the intra-octahedron distortions (i.e. Δd and σ 2 ) were measured from our DFT-optimized structures as has been suggested by Mitzi group. 43 Δd represents the bond length distortion defined as Δd = ∑ (di -d0) 2 / 6d0 2 (di implies the six Pb-I bond lengths and d0 is the average Pb-I bond length), and σ 2 is the bond angle variance defined as σ 2 = ∑ (θ i -90) 2 12 i = 1 / 11, where θ i denotes the individual cis I-Pb-I bond angles (Fig. 3a). Remarkably, in the compressive micro-strain imposed region (as highlighted with yellow color in Fig. 3b), both Δd and σ 2 increased sharply, implying that the degree of intra-octahedron distortion becomes larger when the lattice shrinkage occurs along the c-axis.
To elucidate how the micro-strain (nanoconfined growth in AAO templates) influences the degree of the intra-octahedron distortion (efficiency of the chirality transfer), we have also calculated the hydrogen bonding length between NH3 + groups of chiral organic spacer and nearest iodine atom of inorganic framework (Fig. 3a). Notably, there are four different distinguishable hydrogen bondings in the unit cell of MBA2PbI4 (denoted as HBtop1, HBtop2, HBbot1, and HBbot2 in Fig. 3a). As shown in Fig. 3c, the asymmetric nature of hydrogen bonding (variance and difference between the hydrogen bonding length) was amplified when the lattice shrinkage occurs along the c-axis (region of negative uniaxial strain and positive biaxial strain as highlighted in Fig. 3c). The DFT calculation results support that the asymmetric behavior of hydrogen bonding between the chiral organic molecules and inorganic framework can be amplified depending on the degree of micro-strain, which can promote the efficient chirality transfer process by increasing the chiral distortion in inorganic framework.
The intensity of resulting CD from chiral 2D OIHPs depends on the quadruple product as expressed by Eq. (3): where V12  This implies that the conformational difference associated with π-π stacking of chiral organic cations cannot fully explain the enhancement in the CD intensity of chiral 2D OIHPs grown in AAO templates. Therefore, we should consider other possible chirality transfer mechanisms.
Very recently, Mitzi et al. discovered that the induced CD of chiral 2D OIHPs do not always accompany structural chirality transfer from organic to inorganic layers manifested by centrosymmetric breaking in inorganic frameworks. 36 Indeed, dipolar interactions between the polarizable π clouds of chiral spacer cations and inorganic layers are crucial for determining the associated electronic structure of chiral 2D OIHPs, thereby giving rise to chiroptical responses, such as CD and CPPL.
In this regard, we firstly calculated the electronic band structures for strain-free chiral 2D OIHPs by DFT calculations. The frontier orbitals at the band edges are attributed to the inorganic sub-lattice, which is consistent with previously reported Pb-based OIHPs (Fig. 3a). To explicitly prove our hypothesis that multi-polar interactions between chiral spacer cations and inorganic frameworks could be a key for interpreting the chirality transfer phenomena and chiroptical activities of chiral 2D OIHPs, we calculated the associated changes in electronic band structures for confined grown chiral 2D OIHPs when the micro-strain is applied to the lattice of chiral 2D OIHPs. Remarkably, the HOMO level of MBA goes up toward the VBM of PbI4 inorganic frameworks upon compressive strain imposed along the caxis (see yellow regions in Fig. 3c and d). This observation may give rise to the enhanced multi-polar interactions between MBA molecules and PbI4 inorganic frameworks, as the electrons belonging to MBA and PbI4 become closer not only in spatial distance but also in energy level. It is worth mentioning that MBA2PbI4(1-x)Br4x thin films exhibit sharp XRD diffraction peaks assignable to the (002l) planes regardless of the growing substrates and bromide composition, indicating the highly preferred orientation along the c-axis ( Fig. 1d and Supplementary Fig. S10). In addition, the observed peak shift in the iodide-determinant phase (toward higher 2θ degree) suggests that confined growth induces lattice shrinkage along the caxis. Consequently, we need to focus on the shrinkage range in the out-of-plane direction (i.e., negative uniaxial strain and positive biaxial strain; yellow region in Fig. 3c and d)  where µ1, µ2 and r12 are the intensity of each transition dipole and distance between the two transition dipoles, while e i ⃗ is the corresponding unit vector. Here, it is worth to note that the most significant case arises with strong electric-dipole allowed transitions (not magnetic-dipole allowed transition) couple to each other (exciton coupling) due to the huge difference of magnitude between the electric-dipole and magnetic-dipole (i.e., μab >> mab).
[R25] Therefore, the corresponding rotational strength in chiral 2D OIHPs can be approximated by Eq. 3: Combining the Eq.2 and Eq.3, the resulting CD signal from the chiral 2D OIHPs, which is proportional to rotational strength of dipole interaction (R1,2), can be estimated by the following derivation procedure and Eq. 4: where Γ( , 0 ) represents the factor that accounts for the shape of CD signal. [R26] Consequently, based on the Eq. 4, the CD intensity of chiral 2D OIHPs resulting from the dipole interaction between the static dipole moment of chiral organic cation and transition dipole moment of inorganic framework depends on the triple product as expressed by V12[r 12 ⃗•(μ 1 ⃗×μ 2 ⃗)] scaled by V12. Because the statements related with the calculation of CD intensity were deleted in manuscript, no revision was made by this question

Comments on the presentation and additional technical issues:
In this section I comment on aspects of the manuscript presentation that I think ought to be corrected; as well as some other technical issues I noted while reading the manuscript.

Comment 1)
Given the importance of the nano-confined growth in nanopore substrates in this study, this rather clever technique ought to be mentioned at least in the abstract--if not in the title; however, nothing is said about the technique until page 4 of the manuscript.

Comment 2)
The actual material system studied (chiral MBA2PbI4(1-x)Br4x) is not stated until page 6 of the manuscript: It is not stated in the abstract or title; leading one to wonder what x in line 107 on page 4 refers to. The impression given in the title is that a very general analysis will be forth-coming; but that was not the case.

Comment 3)
Line 34 in the abstract is rather unclear: "(different absorption of 2.0 × 10-3 and distinct photoluminescence of 6.4 × 10-2 for left-and right-handed circularly polarized light)" There are terms for what the authors are trying to describe here: "dissymmetry" and "anisotropy factor". I suggest these terms be used.

Comment 6)
Page 4 line 122: "intensities" is not a correct term to use here.

Author's Response:
As per the reviewer's comment, we have corrected it.

Revision made (colored in blue):
(In page 7)

••• This observation implies that unprecedented chiroptical phenomena of templated chiral 2D
OIHPs cannot be explained in terms of the dichotomy between optically active iodidedeterminant phase (chiral space group of P212121) (iodide-determinant phase) and optically non-active bromide-determinant phase (thermodynamically unfavorable phase) nonchiral space group (bromide-determinant phase), which is based on the prevailing crystal structuredependent chirality transfer mechanism.

Comment 8)
The analysis of micro-strain based on XRD linewidths, shown in Fig 2, is described in the SI in Supplementary Note 2. There the authors state that Scherrer broadening is neglected since chiral OIHPs "have grain size larger than a few hundreds of nanometers". How is that statement relevant to chiral OIHP films grown in nanopore substrates with pore sizes less than ~100nm?

Author's Response:
We thank the reviewer for kind comment about the validity of strain-analysis based on modified Williamson-Hall method. In our manuscript, we mentioned that the "Scherrer broadening would be only significant when the grains are in the nanoscale range. Therefore, we do not expect Scherrer broadening to be a significant contribution in chiral OIHPs that have a grain size larger than a few hundreds of nanometers." As the reviewer pointed out, this description is invalid for the chiral OIHPs films grown in AAO templates with pore size of 66 nm.
However, despite of the pore size (< 100 nm), there are several reasons for excluding the effect of Scherrer broadening when the micro-strain analysis is performed. At first, the Scherrer broadening has a significant effect only if the size of crystalline is the main contribution and all other possible causes for micro-strain are negligible.[R29,R30] However, in the case of chiral 2D OIHPs in AAO templates, the main source of peak broadening is micro-stress imposed by pore wall of AAO templates. Furthermore, although the lateral crystalline size of chiral 2D OIHPs in AAO templates with pore size of 66 nm is less than 100 nm due to the nanoconfinement, the vertical size of the crystal is larger than 100 nm (please see our Response to Comment 1 for Reviewer 2). Therefore, we can conclude that as ∆d strain ≫ ∆d size , the microstrain value of chiral 2D OIHPs imposed by nanoconfinement growth can be calculated by the following equation: (∆d obs 2 -∆d inst 2 ) 1/2 ≈ ∆d strain = ε·d .

(Supplementary Note 2)
••• We note that Scherrer broadening would only be significant when the grains are in the nanoscale range. when the size of crystal is the main contribution of peak broadening and all other possible causes for micro-strain are negligible. In addition, as shown in Supplementary   Fig. S2, the vertical size of the crystal is larger than 100 nm. Therefore, we do not expect Scherrer broadening to be a significant contribution in chiral OIHPs., which have a grain size larger than a few hundreds of nanometers. Micro-strain is the relative change in the size of materials with respect to its thermodynamic ideal size (or size before experiencing an external

Author's Response:
Thanks for the comments. We corrected it in the revised manuscript as the reviewer suggested.
However, we partially agree with the comment about the physical information from the CD and CPPL. The absorption process (CD) starts from a selected subset of vibrational states in ground state and proceeds to many vibrational states in an excited electronic state (thus containing much information on the excited electronic state's vibrational properties). In contrast, the emission process (CPPL) starts from a selected subset of vibrational states of the electronic excited state and proceeds to many possible vibrational states in the ground electron state's vibrational manifold (thus providing information on the ground state's vibrational structure). From this perspective, we have mentioned that "The CPPL spectra give useful information on the ground state of chiral 2D OIHPs, whereas CD spectroscopy can provide information regarding the electronic structure of the excited state of materials" in our manuscript. Of course, as the reviewer pointed out, the CPPL spectra can be highly influenced by the spin and energy relaxation process, making it difficult to interpret meaningfully.
Therefore, to probe the electronic structure of chiral 2D OIHPs, it is necessary to investigate these complementary spectroscopies (both CD and CPPL) rather than using each separately.

Revision made (colored in blue):
( Fig.2c and caption of Fig. 2 was modified)

(In page 14)
The CPPL spectra give useful information on the ground state of chiral 2D OIHPs, whereas CD spectroscopy can provide information regarding the electronic structure of the excited state of materials. 34 However, as the CPPL spectra can be highly influenced by the spin and energy relaxation process, it is difficult to derive the information of electronic structure by itself alone.
Therefore, these complementary spectroscopies are powerful tools for probing the electronic structure of chiral 2D OIHPs. Therefore, to probe the electronic structure of chiral 2D OIHPs, it is necessary to investigate these complementary spectroscopies (both CD and CPPL) rather than using each separately.

<Reviewer 4>
In the article "Multi-Polar Interaction: The Origin of Chiroptical Activity in Chiral 2D Perovskites" the authors investigated 2D hybrid organic-inorganic perovskites having chirooptical activity. In particular they focus on MBA2PbI4(1-x)Br4x systems. The study involves both experimental characterization and theoretical explanations, mainly based on Density Functional Theory (DFT) calculations.
Starting from experimental characterization of the optical activity due to the chirality of the structure, they proposed a theoretical interpretation in terms of an indirect interaction (there is no chemical bonding) between organic spacers (chiral molecular cations) and the framework.
We discussions seem appropriate and supported both from experiments and calculations.
I believe that the article will be interesting for the large community working on hybrid perovskites, and certainly, 2D Chiral HIOPs are an hot topic in material science. Therefore, I recommend publication in Nat. Comm.

Remark:
We would like to thank the reviewer for evaluating our work as an interesting new idea to clarify the origin/mechanism of chiroptical activities in metal halide systems. Our response to the reviewer's comments can be found below.
A quadruple product involves 4 vectors, and it can be either scalar or vector quadruple product.
In this case, V12 is simply a scalar quantity (Davydov splitting), which acts as a scale factor.
Therefore, I would refer to a triple product (the quantity in square brackets), scaled by V12.

Author's Response:
Thanks for the comments. Because the statements related with the calculation of CD intensity were deleted in manuscript, no revision was made by this question 1. The title and abstract and abstract of the revised submission are much more appropriate in the resubmitted version. 2. The revised discussion of the strain and strain analysis is helpful. 3. The addition of absorption spectra are useful and appreciated additions. 4. The Authors have significantly revised and clarified the discussion pertaining to the Davydov splitting which previously seemed to imply that the CD response at the exciton peak was due to the interaction of the MBA1 and MBA2 transition dipoles and the involvement of a resonant state involving the MBA HOMO and the PbI4 framework-this discussion has now been deleted and a revised explanation involving "organic-to-inorganic chirality transfer via hydrogen-bonding interaction changes between the chiral organic spacer and inorganic framework" has been put forward, which seems more plausible. 5. The additions made in response to Referee#2's comment 5 & 7 regarding the possible role of optical anisotropy either associated with, or induced by, the AAO templates, and the need for measurements on racemic samples grown in AAO templates, comprise very important control experiments and are an important addition. 6. I thank the Authors for their explanation of Eq. 3 in the original submission, --I now understand that this is an expression derived for chiral molecules with coupled chromophores with electric dipole allowed/magnetic dipole forbidden transitions; with a twist in their relative orientation. Eq 3 and the discussion of it have been deleted in the resubmitted version. Nevertheless, their explanation greatly clarified (for me) the meaning and context of Fig 2c. Some issues that the authors ought to address in my opinion: 1. In their response to Referee 2 comment 6, and to Referee 3 comment 3 the Authors state that " the positive and negative area of Cotton effect cannot be completely symmetrical." The Authors have cited Berova, Chem. Soc. Rev. 2007, 36, 914-931 (2007, R26 in their rebuttal letter. So, how does this statement square against the CD sum rule, as articulated by Berova? See Eq. 6 and the discussion of it in the Berova paper. Berova et al. state: "the integral of CD over the whole electromagnetic spectrum is zero" and go on to state: "According to this rule if we see a positive CD band in a spectral region, somewhere else in the spectrum we can expect on or more bands of negative sign" ...although it may be hidden in an overlooked region of the spectrum to paraphrase. That seems unlikely to be the case here. 2. Following on from the last point, "apparent CD" (as opposed to true CD) due to optical anisotropy has a mono-signate characteristic (see Salij et al.,https://doi.org/10.1021/jacs.1c06752).
While the control experiments made in response to the comments of Referee #2 (measurements on AAO substrates and on racemic samples grown on AAO substrates) seem rather compelling, have the Authors tried the simple expedient of flipping the sample orientation in the CD spectrometer to confirm that the sign of the CD does not change upon flipping the sample? That would be the tell-tale test that what is being measured is true CD versus apparent CD induced by optical anisotropy. If this were my experiment, I would do this test.
3. Eq 3 has been deleted but it appears subsequent equations were not renumbered.

A comment on the use and definition of the term "multi-polar interaction" .
The Authors use the term "multi-polar interaction" several places in the resubmitted manuscript (line 354, line 428, line 431, line 440, Fig 4). This term pervaded the original submission starting with the title... But I don't see it defined.
It appears to me that the Authors largely replaced the term "multipolar interactions" with the term "asymmetric hydrogen-bonding interaction". (....but did so only in roughly the first half of the manuscript). Is this what the authors mean by the term "multipolar interactions"?
For example, in the original submission, the abstract stated, "Here, through the nano-confined growth of chiral perovskites (MBA2PbI4(1x)Br4x), we verified that the multi-polar interaction between chiral molecular spacers and the inorganic framework plays a key role in promoting the chiroptical activity of chiral perovskites.".
This sentence has been replaced in the resubmission by, "Here, through the nano-confined 30 growth of chiral perovskites (MBA2PbI4(1x)Br4x), we verified that the asymmetric hydrogen-bonding interaction between chiral molecular spacers and the inorganic framework plays a key role in promoting the chiroptical activity of chiral perovskites" Similar replacement in line 92, etc.
So: if the Authors intend that "multipolar interactions" means "asymmetric hydrogen-bonding interaction", could the Authors simply state that this is the case? If not, could the Authors please clarify?
Then: What does the term "multi-polar interaction" have to do with the contents of Fig 4, which is titled: Effects of multi-polar interaction on the electronic structure of chiral 2D OIHPs . Fig 4 shows measured CPPL on chiral 2D OIHPs thin films with different growing substrates. It is an inference to connect that to "multi-polar interaction" since Fig 4 adds nothing to understanding these "multipolar interactions" per se.
Since the term "multi-polar interaction" is important enough to highlight it in the Discussion section and in Fig. 4: I suggest the Authors define precisely what they mean by the term. OR replace it if by this term they actually mean "asymmetric hydrogen-bonding interaction" as seems to be the case.
5. Regarding the discussion of the Davydov splitting Eq. 2 and Fig. 2c: This concept and discussion pertains to one particular mechanism of CD, pertaining to the interaction of independent chromophores whose excitonic transitions are purely electric dipole allowed, magnetic dipole forbidden, and that interact via the Davydov mechanism. This is as opposed, for example, to the Rosenfeld mechanism where the CD is proportional to ⋅ where is the electric dipole moment and is the magnetic dipole moment.
While its applicability could be debated (since it was developed for Frenkel exciton systems, yet they are applying it in a system that supports delocalized Wannier type excitons)... the correlations shown in Fig 2 are certainly interesting/evocative and will provoke discussion.
It would be helpful to readers (like me) to cite some of the literature on the Davydov/exciton model---since I didn't get the context originally without additional response from the authors and additional study of the literature.

Summary:
The resubmitted manuscript is greatly improved and contains quite interesting data and inferences. In my opinion the manuscript would be a good publication however the questions above ought to be addressed by the authors.
Reviewer #4 (Remarks to the Author): The authors reported an joint experimental and theoretical study focussing on a booming subfield of hybrid perovskites, i.e. chiral perovskites.
The authors replied in great details and extensively to all the referees' comments and questions. The article has been significantly improved.
There are reasons to believe that this article will be a reference study for future studies on the same topics.
I suggest publication in Nature Communications.

<Reviewer 2>
The authors have answered most of my questions except my comment #5. The optical anisotropy I mentioned is from the chiral perovskite nanowires rather than AAO templete. In this case, the authors are suggested to consider how the optical anisotropy of perovskite nanowires affects the CD signal. After the authors addressed this question, I would like to recommend its publication.

Remark:
Our response to the reviewer's comments can be found below.

Comment 1:
My most concern is the optical anisotropy of the samples grown on AAO substrates. For those samples, large optical anisotropy could be expected, which would greatly affect the accuracy of the measured CD signals and CPL. If this occurs, any conclusion obtained in this manuscript needs to be reconsidered. Or how can the authors exclude the influence from the optical anisotropy of the samples?

Author's Response:
We appreciate the reviewer's valuable comment on the optical anisotropy which can be originated from the macroscopic anisotropy of perovskite grown in AAO templates. As the reviewer commented, the inherent macroscopic optical anisotropy of perovskite grown in AAO templates may interfere with the origin of chiroptical activity in chiral 2D OIHP. However, it is worth to note that the strain-imposed chiral 2D perovskites grew as an ellipsoid-shaped single crystal rather than nanowire as shown in Fig When investigating the chiroptical activities of thin films with macroscopic anisotropy, we need to recall a basic concept of Mueller matrix analysis; because the observed CD signal (CDobs) is the sum of various contributions, which can be represented by the equation (1): where the first term refers to genuine CD, while the second term accounts for LDLB effect contributions (the signal of which is taken along an arbitrary axis defined in the laboratory frame and where the prime indicates a 45° axis rotation).
[R1] As previous studies have reported that significant contribution of LDLB effect can contaminate the true chiroptical response in crystalline samples with macroscopic anisotropy, we need to exclude the influence of LDLB contribution to explain the true effect of spatial confined growth on chiroptical activity of chiral 2D perovskites. Since the LDLB effect contribution inverts upon sample flipping (i.e., flipping the sample by 180° with respect to the light propagation axis), the CDtrue and LDLB contribution term can be obtained separately by taking semi-sum and semidifference of the two CD spectra with different measurement direction, (i.e., front and back).
CD true = 0.5 × (CD obs, front + CD obs, back ) (2) LDLB = 0.5 × (CD obs, front -CD obs, back ) To eliminate the undesirable contamination from the LDLB effect and clarify the effect of nanoconfined growth on chiroptical phenomena, we have additionally conducted the CD measurement on chiral 2D perovskite in AAO templates with 100 nm pore size by varying the incident light direction (i.e., front and back). Interestingly, as shown in Fig. R2, both of chiral 2D perovskites thin films exhibited the huge increment in CD signal under the backward measurement condition, regardless of the grown substrate conditions (e.g., planar and 100 nmpore sized AAO template). Furthermore, we isolated CDtrue and LDLB contribution by using equation (2) and (3), demonstrating that the effect of nanoconfined growth in AAO template (i.e., huge amplification of CD signal) can be also clearly observed in CDtrue spectra (Fig. R3b).
As the CDtrue and LDLB contributions for AAO sample have opposite sign near the first extinction band edge (around 475 nm), the effect of nanoconfined growth on chiroptical phenomena in our manuscript was underestimated rather than overestimated; the difference of apparent CD spectra (CDobs) between the planar and AAO template conditions (Fig. R3a, which is reproduced from Fig. 1a in our manuscripts) is smaller than that of genuine CD signal (CDtrue in Fig. R3b). This result demonstrates that the effect of the optical anisotropy resulted from the macroscopic nature can be completely excluded from our experimental results, interpretation, and conclusion. Consequently, it can be concluded that correlation between the deviation of chiroptical activities and the resulting micro-strain induced by the nanoconfined growth, which is a core objective of this paper, is well supported by experimental results and strain analysis.   2. The revised discussion of the strain and strain analysis is helpful.
3. The addition of absorption spectra are useful and appreciated additions.
4. The Authors have significantly revised and clarified the discussion pertaining to the Davydov splitting which previously seemed to imply that the CD response at the exciton peak was due to the interaction of the MBA1 and MBA2 transition dipoles and the involvement of a resonant state involving the MBA HOMO and the PbI4 framework-this discussion has now been deleted and a revised explanation involving organic-to-inorganic chirality transfer via hydrogenbonding interaction changes between the chiral organic spacer and inorganic framework has been put forward, which seems more plausible.

Remark:
We would like to thank the reviewer for improving our work by suggesting an interesting new idea and possible explanation based on theoretical basis. Our response to the reviewer's comments can be found below.

Comment 1:
In their response to Referee 2 comment 6, and to Referee 3 comment 3 the Authors state that " the positive and negative area of Cotton effect cannot be completely symmetrical." The Authors have cited Berova, Chem. Soc. Rev. 2007, 36, 914-931 (2007, R26 in their rebuttal letter. So, how does this statement square against the CD sum rule, as articulated by Berova? See Eq. 6 and the discussion of it in the Berova paper. Berova et al. state: "the integral of CD over the whole electromagnetic spectrum is zero" and go on to state: "According to this rule if we see a positive CD band in a spectral region, somewhere else in the spectrum we can expect one or more bands of negative sign" …although it may be hidden in an overlooked region of the spectrum to paraphrase. That seems unlikely to be the case here.

Author's Response:
As the reviewer commented, according to the CD sum rule, if we see a positive CD band in a spectral region, somewhere else in the spectrum we can expect one or more bands of negative sign. Therefore, the discrepancy between the area of the positive and negative Cotton effect around the first extinction band edge in chiral 2D perovskite (around 475 nm) should be compensated for somewhere in the electromagnetic spectrum. As shown in Fig. R4, of course, the expanded CD spectra of chiral 2D perovskites showed additional CD signal and followed the CD sum rule as Berova mentioned. The additional CD signal results from the excitonic transition state of the perovskite, which is far from the MBA cation exciton transition (~ 260 nm). Since we mainly focused on the chiroptical phenomena near the first extinction band edge, where the intensive excitonic transition behavior occurs, and it is quite natural to satisfy the CD sum rule in electromagnetic spectrum, no revision was made by this question. Following on from the last point, "apparent CD" (as opposed to true CD) due to optical anisotropy has a mono-signate characteristic (see Salij et al.,).

Author's Response:
We thank the reviewer for the critical comment on the interpretation and validity of CD spectra.
As the reviewer suggested, to clarify the true CD associated with the excitonic transition and exclude the LDLB contribution term induced by macroscopic optical anisotropy, we have additionally conducted CD measurement by flipping the samples. Interestingly, as shown in Reviewer 2). Furthermore, in our chiral 2D perovskite grown in AAO templates, since the LDLB effect negatively contributed to the apparent CD, the calculated true CD spectra revealed that the effect of nanoconfined growth by AAO template on chiroptical activities was underestimated in the apparent CD spectra ( Fig. 1 in our manuscript).
To quantitatively compare the contribution between CDtrue and LDLB effect to the apparent CD signal, [R4] the absolute integral area value of each spectrum (CDtrue and LDLB) was calculated, and the corresponding values were shown in Table R1. Although the LDLB effect contribution can be clearly recognized in chiral 2D perovskite grown in AAO templates, the integral ratio of LDLB/CDtrue (0.46 for planar and 0.47 for AAO template) confirmed that CDtrue term has more contribution to apparent CD spectra than LDLB effect. In addition, the integral ratio of two samples was very similar, implying that observed LDLB effect stems from the preferential orientation of chiral 2D perovskite itself (i.e., preferred orientation of (002l) plane) rather than optical anisotropic nature of grown substrates. We appreciate the reviewer for suggesting the possible direction of the future work on exploiting the LDLB signal and genuine light-mater interaction. Please understand that the results of chiroptical measurement, including the sample flipping experiment, are not added in the revised manuscript, because the origin of existing LDLB effect and contribution to apparent CD observed in chiral 2D perovskite will be an interesting future research topic.

Comment 3:
Eq 3 has been deleted but it appears subsequent equations were not renumbered.

Author's Response:
As the reviewer's pointed out, subsequent equations were renumbered. Since the equation, which is related with the approximation of rotational strength, was added as equation (3), the number of following definition about asymmetry factor of CPPL was not changed.

Revision made (colored in blue):
(in page 13) ••• following definition: where IL and IR are the intensities of LCP and RCP light photoluminescence, respectively. ••• A comment on the use and definition of the term "multi-polar interaction". The Authors use the term "multi-polar interaction" several places in the resubmitted manuscript (line 354, line 428, line 431, line 440, Fig 4). This term pervaded the original submission starting with the title… But I don't see it defined. It appears to me that the Authors largely replaced the term "multipolar interactions" with the term "asymmetric hydrogen-bonding interaction". (….but did so only in roughly the first half of the manuscript). Is this what the authors mean by the term "multipolar interactions"?

Author's Response:
Thank you for the comment. When we used the term of multi-polar interaction, it was intended to mention the type of electronic interaction between the two building blocks (i.e., chiral molecules and achiral inorganic frameworks). However, in our resubmitted manuscript, it is clear that the origin of chiroptical behavior in chiral 2D perovskites is related with the asymmetric hydrogen-bonding interaction rather than multi-polar interaction (or resonant electronic interaction between the chiral molecules and inorganic framework). Therefore, in order to remove the possibility of confusion, we have replaced the term of multi-polar interaction with the term of asymmetric hydrogen-bonding interaction.

Revision made (colored in blue):
(in page 14) ••• to investigate the effects of multi-polar interaction asymmetric hydrogen-bonding induced by confined growth on the electronic structure of chiral 2D OIHPs •••

(in page 17)
Consequently, it can be concluded that the amplified chiroptical activity in AAO templated chiral 2D OIHPs is more affected by the multi-polar interaction asymmetric hydrogen-bonding interaction between MBA cations and the inorganic framework rather than the structural distortion in the inorganic framework itself. Our findings suggest that the degree of chirality Regarding the discussion of the Davydov splitting Eq. 2 and Fig. 2c: This concept and discussion pertains to one particular mechanism of CD, pertaining to the interaction of independent chromophores whose excitonic transitions are purely electric dipole allowed, magnetic dipole forbidden, and that interact via the Davydov mechanism. This is as opposed, for example, to the Rosenfeld mechanism where the CD is proportional to ⋅ where is the electric dipole moment and is the magnetic dipole moment. While its applicability could be debated (since it was developed for Frenkel exciton systems, yet they are applying it in a system that supports delocalized Wannier type excitons)… the correlations shown in Fig 2 are certainly interesting/evocative and will provoke discussion. It would be helpful to readers (like me) to cite some of the literature on the Davydov/exciton model---since I didn't get the context originally without additional response from the authors and additional study of the literature.

Author's Response:
Thank you for the comment. As reviewer pointed out, Davydov model considers an ideal system, which consist of independent chromophores with degenerated excited states. When those independent chromophores are spatially close enough to one another, the interaction between the transition moments of the component chromophores occurs, resulting in coupling of the chromophores.
[R5] Therefore, we agreed with the comment that applicability of Davydov model in chiral perovskite system with Wannier type excitons could be controversial.
In order to dimmish the possibility of misunderstanding and to secure the versatility of interpretations applicable to various system with optical activities, we have substituted the term of "Davydov splitting" with the more general term of "excited state splitting". [R6] By applying perturbation theory, the originally degenerated excited level splits into the two states separated by 2V12, which is now referred to as the excited state splitting. In this respect, the intensity of characteristic CD signal is proportional to the rotational strength (R) by the following equation (4), which considers the interaction between the electric dipole moments 1 and 2 and also includes the terms relating to the coupling of μ and m by Rosenfield mechanism.[R7,R8] We modified the expression, which is related to Davydov splitting and some of literature about the interpretation of chiroptical activities in exciton model were added in revised manuscript as reviewer suggested.
It is worth to noting that the abnormal chiroptical behaviors •••

(in page 12)
To verify the relationship between the imposed micro-strain and the efficiency of chirality transfer in chiral 2D OIHPs, we evaluated the excited state splitting Davydov splitting values from the deconvoluted CD spectra where a bisginate CD signal appeared around the extinction band edge λ 0 . Using a multiple-peak fitting function, several peaks in chiral 2D OIHPs with various halide composition were identifiable (Supplementary Fig. S12; see Supplementary Note 4 for the detailed procedures and validity). The experimentally determined Davydov splitting excited state splitting values for chiral 2D OIHPs, 2V12, are plotted in Fig. 2d as a function of the pore size of the AAO template (pore size = 0 for the planar substrate).
Interestingly, in the entire composition range (from x = 0.325 to x = 0.400), the corresponding variation in Davydov splitting excited state splitting also exhibited a zigzag tendency, which is similar to the calculated micro-strain results (Fig. 2b)

REVIEWERS' COMMENTS
Reviewer #2 (Remarks to the Author): I have no further question and would like to recommend its publication at the current form.
Reviewer #3 (Remarks to the Author): Please see attached PDF containing my comments.

Manuscript number: Nature Communications manuscript NCOMMS-21-30935B
Title: Elucidating the origin of chiroptical activity in chiral 2D perovskites through nanoconfined growth Authors: Sunihl Ma et al.

Synopsis:
I have reviewed Authors' response, re-read the previous correspondence and read the new revised manuscript. The main features of the work are, to summarize, 1. Mixed anion chiral 2D perovskite samples are grown at a composition which is on the edge of a phase transition between a chiral phase (iodine rich) and a nonchiral phase (Br rich) (J. Am. Chem. Soc. 2020, 142); 2. Growth of this material in AAO substrates results in oriented nanoconfined growth of single domain nanocrystals that are in a state of negative uniaxial strain and positive biaxial strain; 3. The degree of micro-strain in the samples appears to correlate with the excited state splitting when the bi-signate CD spectra are interpreted in terms of a molecular Frenkel exciton model (Fig 2); 4. The AAO samples exhibit rather high degree of circularly polarized PL (Fig 4) 5. DFT calculations are performed which suggest the compressive micro-strain is connected with intra-octahedral distortions perhaps due to changes in hydrogen bonding, pointing to a mechanism for strain enhancement of chirality transfer from the chiral organic cations to the inorganic framework.
This is all good, and in my opinion will be really interesting for the community.

A couple issues:
1) Whether to include the apparent-CD data that came out in the back and forth over the referee comments.
In the last round of review I had suggested (following on to a question about optical anisotropy first posed by Referee #2) that the authors examine the possibility that the measured CD signal in their chiral perovskite samples grown in AAO templates may be due to the phenomenon of "apparent CD"-which can be easily tested by the simple expedient of comparing the observed CD response measuring the sample from the front side versus the backside directions. If true CD is being measured, the spectra should be identical whether measured forward or backward. If the sign of the observed CD changes, then there is an "apparent CD" response which originates from an interference of linear dichroism and linear birefringence (the so called "LD/LB" signal).
The authors performed this test and reported back the results in Fig R2 and R3. The results were surprising: The CD amplitude measured in the backwards direction is roughly 6 times larger than measured in the forward direction ( Fig R2). The authors define "true CD" and non-CD "LD/LB" spectra as the sum and difference of the forward and backward measured spectra (this is the common way this would be done) and then show bi-signate LD/LB spectra which are opposite in sign to the bisignate "true CD" response measured in the forward direction.
They argue that the implication is therefore that the CD enhancement due to growth in micropores was previously under-reported, and that since the true CD response is greater than 50% of the signal (Table R1 gives the integrated area of the LB/LB spectra as 47%), none of the conclusions really change. They then state that they did not add these "apparent CD" data to the revised manuscript because this will be a subject of future research, writing: "We appreciate the reviewer for suggesting the possible direction of the future work on exploiting the LDLB signal and genuine light-mater interaction. Please understand that the results of chiroptical measurement including the sample flipping experiment, are not added in the revised manuscript, because the origin of existing LDLB effect and contribution to apparent CD observed in chiral 2D perovskite will be an interesting future research topic." In my opinion, this data should be included. Just my opinion but, the question addressed in this manuscript is basically: "what is the mechanism for the enhanced CD response observed in the chiral perovskites grown in nanopore templates, and what, if anything does this contribute to the general understanding of the chiroptic response at the exciton line in chiral 2D perovskite semiconductors, which is so far essentially not understood?". The directional dependence of the enhanced response is unexpected and is totally relevant to the question. It may be awkward to include this data, because it is hard to explain what the authors observed (i.e. its not understood at this point) but it is certainly relevant to complete picture of/understanding of the work.
2. General clarity: I suggest that the authors go through the paper once more and make that everything is described in consistent and clear terms since the theoretical model and some of explanations have evolved quite a bit in the course of the referee comments & discussion... The issue I raised about "multipolar interactions" vs hydrogen bonding interactions is an example which the authors addressed in this new revision at my request. There are a few other statements that have crept in that I think are rather unclear or questionable, such as, on page 16, To exclude the effect of Rashba splitting on CPPL spectra, which might arise from the experimental procedure (because the excitation by the circularly polarized light can lift the degeneracy of spin state due to the large spin-orbit coupling (SOC) of OIHPs), And, coherent lifting of the spin degeneracy by the circularly polarized light.
These statement need references as it is not at all clear (to me) what they are taking about; are the authors are referring to the work by Adarsh or ? Conventional 2D-Rashba splitting in 2D systems produces spin textures that are not compatible with chiroptic effects, so such statements should be clarified with additional prose or references that indicate what they mean.

<Reviewer 3>
Comment 1: Whether to include the apparent-CD data that came out in the back and forth over the referee comments. In my opinion, this data should be included. Just my opinion but, the question addressed in this manuscript is basically: "what is the mechanism for the enhanced CD response observed in the chiral perovskites grown in nanopore templates, and what, if anything does this contribute to the general understanding of the chiroptic response at the exciton line in chiral 2D perovskite semiconductors, which is so far essentially not understood?". The directional dependence of the enhanced response is unexpected and is totally relevant to the question. It may be awkward to include this data, because it is hard to explain what the authors observed (i.e. its not understood at this point) but it is certainly relevant to complete picture of/understanding of the work.

Author's Response:
We appreciate the reviewer's valuable comment on the apparent-CD data observed in the chiral OIHPs grown inside the AAO templates. Although it is difficult to explain the directional dependence of the enhanced chiroptical activity in chiral OIHPs grown in the AAO templates, we decided to provide the apparent CD data and related explanations in our revised manuscript as the reviewer suggested. We would like to thank the reviewer for improving our work.

Revision made (colored in blue):
(in page 6) ••• This implies that the effect of the optical anisotropy from the bare AAO templates can be completely excluded.
Recently, Di Bari and co-workers have reported that several organic thin films with macroscopic anisotropy can exhibit unexpected CD signal with a strong dependence on the light propagation direction (angle of incident light during the chiroptical measurement), 36,37 which stems from the optical interference of thin film's linear birefringence (LB) and linear dichroism (LD) (hereafter LDLB effect) rather than excitonic effects. Therefore, when investigating the chiroptical activities of thin films with macroscopic anisotropy, we need to consider a basic concept of Mueller matrix analysis; because the observed CD signal (CDobs) is the sum of various contributions as represented by the equation (2): where the first term refers to genuine CD, while the second term accounts for LDLB effect contribution (the signal of which is taken along an arbitrary axis defined in the laboratory frame and where the prime indicates a 45° axis rotation). It is necessary to exclude the influence of LDLB contribution to explain the true effect of spatial confined growth on chiroptical activity of chiral 2D perovskites. Since the LDLB effect contribution is inverted upon sample flipping (i.e., flipping the sample by 180° with respect to the light propagation axis), the CDtrue term can be separately obtained by taking semi-sum of the two CD spectra with different measurement directions, (i.e., front and back).
CD true = 0.5 × (CD obs, front + CD obs, back ) The effect of nanoconfined growth in AAO template (i.e., huge amplification of CD signal) can be clearly observed in CDtrue spectra ( Supplementary Fig. S4b), where the effect of the optical anisotropy resulted from the macroscopic nature is completely excluded. Consequently, it can be concluded that the observed chiroptical activities in the AAO templated chiral 2D OIHPs (e.g., huge amplification of the absolute gCD value, sign conversion, and spectral shape change of Cotton effect) are attributed to effect of spatial confined growth of chiral 2D OIHPs rather than optical anisotropy from the bare AAO templates and macroscopic anisotropy of chiral 2D OIHPs. Therefore, the observed sign conversion and spectral shape change of the Cotton effect imply that spatial confinement by AAO templates might induce the coupling 3 modulation between the chiral chromophores, resulting in the reconstruction of the chiroptical band structure.
(Apparent-CD measurement data were added in Supplementary as Fig. S4) General clarity: I suggest that the authors go through the paper once more and make that everything is described in consistent and clear terms since the theoretical model and some of explanations have evolved quite a bit in the course of the referee comments & discussion… The issue I raised about "multipolar interactions" vs hydrogen bonding interactions is an example which the authors addressed in this new revision at my request. Furthermore, in the presence of applied magnetic field (about 1T  5T), the circularly polarized light (CPPL) can be observed even in racemic compounds and 3D OIHPs without chirality transfer phenomena due to the field-induced population changes among the spin sublevels. [R4,R5] Compare to the unpolarized light, which consist of many electromagnetic waves polarized in different directions (i.e., net electric and magnetic field are zero), circularly polarized light (CPL) is polarized only in one direction by passing through the polarizing filter, so that both of the electric and magnetic field exist. Although the effective magnitude of external magnetic field for magneto-CPPL is quite large (as aforementioned; 1T  5T) compared to the magnetic field in CPL, the excitation by CPL source can give rise to CPPL due to the field-effect rather chirality transfer phenomena. Therefore, to exclude all the potential possibilities of field-effect induced CPPL, which might arise from the CPL excitation source, the CPPL measurement was also performed in the same manner (using circular polarized light as an excitation source) for racemic compounds grown inside AAO templates with pore size of 100 nm as presented in Fig. S14 (Supplementary). In order to dimmish the possibility of misunderstanding and to secure the reliability of interpretations on CPPL measurement using CPL excitation source, we have modified relevant statements and added additional reference for clarity as reviewer suggested.

Revision made (colored in blue):
(in page 16) Due to the heavy atoms in OIHPs, large spin-orbit coupling (SOC) of OIHPs can lift the degeneracy of spin state and lead to large Rashba splitting if the structure lacks inversion symmetry. 50,51 Furthermore, in the presence of applied magnetic field (about 1T  5T), the CPPL can be observed even in racemic compounds and 3D OIHPs without chirality transfer phenomena due to the field-induced population changes among the spin sublevels. 18,21 Compare to the unpolarized light, which consist of many electromagnetic waves polarized in different directions (i.e., net electric and magnetic field are zero), CPL is polarized only in one direction by passing through the polarizing filter, so that both of the electric and magnetic field exist. Although the effective magnitude of external magnetic field for magneto-CPPL is quite large (as aforementioned; 1T  5T) compared to the magnetic field in CPL, the excitation by CPL source can give rise to CPPL due to the field-effect rather chirality transfer phenomena.
To exclude the effect of Rashba splitting due to large SOC of OIHPs on CPPL spectra, which might arise from the experimental procedure (because of the magnetic field in CPL excitation by the circularly polarized light can lift the degeneracy of spin state due to the large spin-orbit coupling (SOC) of OIHPs), and to clarify the origin of different emission rate of RCP and LCP, the CPPL measurement was also performed in the same manner (using circular polarized light as a excitation source) for racemic compounds grown on AAO templates with pore size of 100 nm. As shown in Fig. S15 (Supplementary), the racemic compounds grown in AAO templates do not show any different emission behavior between the RCP and LCP. The CPPL spectra of racemic compounds grown on AAO templates suggested that the Rashba effect and coherent lifting of the spin degeneracy induced by the SOC of OIHPs circularly polarized light did not occur in the absence of chirality transfer phenomena (i.e., in the absence of chiral organic molecules). This implies that enhanced asymmetric factor of CPPL (gCPPL) in chiral 2D OIHPs results from the facilitated chirality transfer phenomena rather than Rashba effect itself (induced by the large SOC of OIHPs excitation using circular polarized light). Very recently, Mitzi group found that the Rashba-Dresselhaus spin-splitting is a consequence of the chirality transfer phenomena. 52 •••