Chiral π-conjugated molecules bring new functionality to technological applications and represent an exciting, rapidly expanding area of research. Their functional properties, such as the absorption and emission of circularly polarized light or the transport of spin-polarized electrons, are highly anisotropic. As a result, the orientation of chiral molecules critically determines the functionality and efficiency of chiral devices. Here we present a strategy to control the orientation of a small chiral molecule (2,2′-dicyanohelicene) by the use of organic and inorganic templating layers. Such templating layers can either force 2,2′-dicyanohelicene to adopt a face-on orientation and self-assemble into upright supramolecular columns oriented with their helical axis perpendicular to the substrate, or an edge-on orientation with parallel-lying supramolecular columns. Through such control, we show that low- and high-energy chiroptical responses can be independently ‘turned on’ or ‘turned off’. The templating methodologies described here provide a simple way to engineer orientational control and, by association, anisotropic functional properties of chiral molecular systems for a range of emerging technologies.
This is a preview of subscription content, access via your institution
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Rent or buy this article
Get just this article for as long as you need it
Prices may be subject to local taxes which are calculated during checkout
Source data are provided with this paper. Data for the main and extended figures are available at https://doi.org/10.14469/hpc/10763.
Frédéric, L., Desmarchelier, A., Favereau, L. & Pieters, G. Designs and applications of circularly polarized thermally activated delayed fluorescence molecules. Adv. Funct. Mater. 31, 2010281 (2021).
Zhang, D.-W., Li, M. & Chen, C.-F. Recent advances in circularly polarized electroluminescence based on organic light-emitting diodes. Chem. Soc. Rev. 49, 1331–1343 (2020).
Schulz, M. et al. Giant intrinsic circular dichroism of prolinol-derived squaraine thin films. Nat. Commun. 9, 2413 (2018).
Schulz, M. et al. Chiral excitonic organic photodiodes for direct detection of circular polarized light. Adv. Funct. Mater. 29, 1900684 (2019).
MacKenzie, L. E. & Pal, R. Circularly polarized lanthanide luminescence for advanced security inks. Nat. Rev. Chem. 5, 109–124 (2021).
Breen, C. et al. Time-resolved luminescence detection of peroxynitrite using a reactivity-based lanthanide probe. Chem. Sci. 11, 3164–3170 (2020).
Shen, Y. & Chen, C. F. Helicenes: synthesis and applications. Chem. Rev. 112, 1463–1535 (2011).
Kettner, M. et al. Chirality-dependent electron spin filtering by molecular monolayers of helicenes. J. Phys. Chem. Lett. 9, 2025–2030 (2018).
Yang, Y., da Costa, R. C., Fuchter, M. J. & Campbell, A. J. Circularly polarized light detection by a chiral organic semiconductor transistor. Nat. Photon. 7, 634–638 (2013).
Kiran, V. et al. Helicenes—a new class of organic spin filter. Adv. Mater. 28, 1957–1962 (2016).
Gingras, M., Félix, G. & Peresutti, R. One hundred years of helicene chemistry. Part 2: stereoselective syntheses and chiral separations of carbohelicenes. Chem. Soc. Rev. 42, 1007–1050 (2013).
Yang, Y. et al. Emergent properties of an organic semiconductor driven by its molecular chirality. ACS Nano 11, 8329–8338 (2017).
Kulkarni, C. et al. Highly efficient and tunable filtering of electrons’ spin by supramolecular chirality of nanofiber‐based materials. Adv. Mater. 32, 1904965 (2020).
Möllers, P. V. et al. Spin‐selective electron transmission through self‐assembled monolayers of double‐stranded peptide nucleic acid. Chirality 33, 93–102 (2021).
Chen, S. H. et al. Circularly polarized light generated by photoexcitation of luminophores in glassy liquid-crystal films. Nature 397, 506–508 (1999).
Maniappan, S., Jadhav, A. B. & Kumar, J. Template assisted generation of chiral luminescence in organic fluorophores. Front. Chem. 8, 557650 (2021).
Baek, K. et al. Simultaneous emission of orthogonal handedness in circular polarization from a single luminophore. Light Sci. Appl. 8, 2047–7538. (2019).
Di Nuzzo, D. et al. High circular polarization of electroluminescence achieved via self-assembly of a light-emitting chiral conjugated polymer into multidomain cholesteric films. ACS Nano 11, 12713–12722 (2017).
Wade, J. et al. Natural optical activity as the origin of the large chiroptical properties in π-conjugated polymer thin films. Nat. Commun. 11, 6137 (2020).
Ernst, K.-H. Stereochemical recognition of helicenes on metal surfaces. Acc. Chem. Res. 49, 1182–1190 (2016).
Ernst, K.-H., Kuster, Y., Fasel, R., Müller, M. & Ellerbeck, U. Two-dimensional separation of helicene enantiomers on Cu(111). Chirality 13, 675–678 (2001).
Fasel, R., Parschau, M. & Ernst, K. H. Amplification of chirality in two-dimensional enantiomorphous lattices. Nature 439, 449–452 (2006).
Krukowski, P. et al. Adsorption and light emission of a racemic mixture of thiaheterohelicene-2,13-carboxaldehyde on Au(111), Cu(001), and NiAl(110) surfaces investigated using a scanning tunneling microscope. J. Phys. Chem. C 125, 9419–9427 (2021).
Seibel, J., Parschau, M. & Ernst, K.-H. Double layer crystallization of heptahelicene on noble metal surfaces. Chirality 32, 975–980 (2020).
Xu, Y. et al. Chirality of molecular nanostructures on surfaces via molecular assembly and reaction: manifestation and control. Surf. Sci. Rep. 76, 100531 (2021).
Stöhr, M. et al. Self-assembly and two-dimensional spontaneous resolution of cyano-functionalized helicenes on Cu(111). Angew. Chem. Int. Ed. 50, 9982–9986 (2011).
Ernst, K.-H. Molecular chirality at surfaces: molecular chirality at surfaces. Phys. Status Solidi 249, 2057–2088 (2012).
Sullivan, P., Jones, T. S., Ferguson, A. J. & Heutz, S. Structural templating as a route to improved photovoltaic performance in copper phthalocyanine/fullerene (C60) heterojunctions. Appl. Phys. Lett. 91, 233114 (2007).
Heutz, S., Cloots, R. & Jones, T. S. Structural templating effects in molecular heterostructures grown by organic molecular-beam deposition. Appl. Phys. Lett. 77, 3938–3940 (2000).
Kim, D. K., Lubert-Perquel, D. & Heutz, S. Comparison of organic and inorganic layers for structural templating of pentacene thin films.Mater. Horizons 7, 289–298 (2020).
Rand, B. P. et al. The impact of molecular orientation on the photovoltaic properties of a phthalocyanine/fullerene heterojunction. Adv. Funct. Mater. 22, 2987–2995 (2012).
Salerno, F. et al. The influence of nitrogen position on charge carrier mobility in enantiopure azahelicene crystals. Phys. Chem. Chem. Phys. 21, 5059–5067 (2019).
Rice, B. et al. A computational exploration of the crystal energy and charge-carrier mobility landscapes of the chiral helicene molecule. Nanoscale 10, 1865–1876 (2018).
Schmidt, J. A. et al. Computational screening of chiral organic semiconductors: exploring side-group functionalization and assembly to optimize charge transport. Cryst. Growth Des. 21, 5036–5049 (2021).
Wachsmann, C., Weber, E., Czugler, M. & Seichter, W. New functional hexahelicenes—synthesis, chiroptical properties, X-ray crystal structures, and comparative data bank analysis of hexahelicenes. Eur. J. Org. Chem. 2003, 2863–2876 (2003).
Breiby, D. W., Bunk, O., Andreasen, J. W., Lemke, H. T. & Nielsen, M. M. Simulating X-ray diffraction of textured films. J. Appl. Crystallogr. 41, 262–271 (2008).
Oh, J. H. et al. Interplay between energetic and kinetic factors on the ambient stability of n-channel organic transistors based on perylene diimide derivatives. Chem. Mater. 21, 5508–5518 (2009).
Ramadan, A. J. et al. Selecting phthalocyanine polymorphs using local chemical termination variations in copper iodide. J. Phys. Chem. C 120, 4448–4452 (2016).
Bhalla, A. S. & White, E. W. Crystallographic polarity determination of γ-CuI. Acta Crystallogr. B 27, 852–853 (1971).
Furche, F. et al. Circular dichroism of helicenes investigated by time-dependent density functional theory. J. Am. Chem. Soc. 122, 1717–1724 (2000).
Macrae, C. F. et al. Mercury 4.0: from visualization to analysis, design and prediction. J. Appl. Crystallogr. 53, 226–235 (2020).
Nečas, D. & Klapetek, P. Gwyddion: an open-source software for SPM data analysis. Cent. Eur. J. Phys. 10, 181–188 (2012).
Jiang, Z. GIXSGUI: a MATLAB toolbox for grazing-incidence X-ray scattering data visualization and reduction, and indexing of buried three-dimensional periodic nanostructured films. J. Appl. Crystallogr. 48, 917–926 (2015).
Frisch, M. J. et al. Gaussian 16 (Gaussian, Inc., 2016).
Becke, A. D. Density‐functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 98, 5648–5652 (1993).
Breneman, C. M. & Wiberg, K. B. Determining atom-centered monopoles from molecular electrostatic potentials. The need for high sampling density in formamide conformational analysis. J. Comput. Chem. 11, 361–373 (1990).
Karamertzanis, P. G. & Pantelides, C. C. Ab initio crystal structure prediction? I. Rigid molecules. J. Comput. Chem. 26, 304–324 (2005).
Karamertzanis, P. G. & Pantelides, C. C. Ab initio crystal structure prediction. II. Flexible molecules. Mol. Phys. 105, 273–291 (2007).
Motherwell, S. & Chisholm, J. A. COMPACK: a program for identifying crystal structure similarity using distances. J. Appl. Crystallogr. 38, 228–231 (2005).
Price, S. L. et al. Modelling organic crystal structures using distributed multipole and polarizability-based model intermolecular potentials. Phys. Chem. Chem. Phys. 12, 8478–8490 (2010).
Williams, D. E. Improved intermolecular force field for molecules containing H, C, N, and O atoms, with application to nucleoside and peptide crystals. J. Comput. Chem. 22, 1154–1166 (2001).
Soler, J. M. et al. The SIESTA method for ab initio order-N materials simulation. J. Phys. Condens. Matter 14, 2745–2779 (2002).
Artacho, E. et al. The SIESTA method; developments and applicability. J. Phys. Condens. Matter 20, 064208 (2008).
Becke, A. D. On the large‐gradient behavior of the density functional exchange energy. J. Chem. Phys. 85, 7184–7187 (1998).
Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).
Johnson, E. R. in Non-Covalent Interactions in Quantum Chemistry and Physics (eds Otero-De-La-Roza, A. & DiLabio, G. A.) 169–192 (Elsevier Inc., 2017).
Otero-De-La-Roza, A. & Johnson, E. R. Van der Waals interactions in solids using the exchange-hole dipole moment model. J. Chem. Phys. 136, 174109 (2012).
LeBlanc, L. M., Weatherby, J. A., Otero-De-La-Roza, A. & Johnson, E. R. Non-covalent interactions in molecular crystals: exploring the accuracy of the exchange-hole dipole moment model with local orbitals. J. Chem. Theory Comput. 14, 5715–5724 (2018).
Giannozzi, P. et al. Advanced capabilities for materials modelling with Quantum ESPRESSO. J. Phys. Condens. Matter 29, 465901 (2017).
Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).
LeBlanc, L. M. & Johnson, E. R. Crystal-energy landscapes of active pharmaceutical ingredients using composite approaches. CrystEngComm 21, 5995–6009 (2019).
Becke, A. Density-functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A 38, 3098–3100 (1988).
Lee, C., Yang, W. & Parr, R. G. Development of the Colle–Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 37, 785–789 (1988).
Kirkpatrick, J. An approximate method for calculating transfer integrals based on the ZINDO Hamiltonian. Int. J. Quantum Chem. 108, 51–56 (2008).
Marcus, R. A. On the theory of oxidation–reduction reactions involving electron transfer. I. J. Chem. Phys. 24, 966–978 (2004).
Sakanoue, K., Motoda, M., Sugimoto, M. & Sakaki, S. A molecular orbital study on the hole transport property of organic amine compounds. J. Phys. Chem. A 103, 5551–5556 (1999).
We thank the EPSRC for funding (EP/R00188X/1, EP/F039948/1 and EP/L016702/1). We also thank the company Xenocs for their help and ongoing support with the X-ray scattering instrument based at The University of Sheffield and we thank the EPSRC for funding the purchase of this instrument. We thank the Department of Materials at Imperial College London for supporting an Imperial College Research Fellowship (JW) and PhD (DK). We thank A. Maho for his assistance with the SEM. We also thank G. Siligardi of the Diamond B23 beamline for his assistance on beamtimes SM29151. This project was supported by access to instrumentation at the Centre for Rapid Online Analysis of Reactions (ROAR) at Imperial College London (EPSRC, EP/R008825/1 and EP/V029037/1). J.N. thanks the European Research Council for the award of an Advanced Grant under Horizon 2020 (action no. 742708), and the Royal Society for a Research Professorship. K.E.J. thanks the Royal Society for a University Research Fellowship and an Enhancement Award and the European Research Council for the award of a Starting Grant under FP7 (CoMMaD, ERC Grant no. 758370). T.M. thanks CREST, JST, Japan for a grant (no. JPMJCR2001). E.R.J. and L.M.L. thank the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Walter C. Sumner Foundation for financial support. We also thank Compute Canada for computational resources.
The authors declare the following competing financial interest(s): M.F. is an inventor on a patent concerning chiral blend materials (WO2014016611).
Peer review information
Nature Chemistry thanks Karl-Heinz Ernst and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended Data Fig. 1 Solution-state absorbance and photoluminescence spectra.
Absorption and photoluminescence spectra of CN6H in acetonitrile (2·10 − 5 M). The excitation wavelength was 325 nm.
Extended Data Fig. 2 UV-Visible absorption and circular dichroism of neat templating layers.
(a)UV-Vis and Circular Dichroism of the templating layers (PTCDA: 20 nm, CuI: 100 nm). (b)UV-Vis of CN6H [M] thin films subtracting the absorbance of the templating layers.
Extended Data Fig. 3 UV-Visible absorption and photoluminescence spectra of CN6H thin films.
(a)UV-visible absorption spectra of CN6H thin films (thickness: 78 nm) on a non-interacting substrate (quartz, black line), 20 nm PTCDA (red) and 100 nm CuI (111) (blue line). (b) Photoluminescence spectra of CN6H thin films (thickness: 78 nm) on a non-interacting substrate (quartz, black line), 20 nm PTCDA (red) and 100 nm CuI (111) (blue line). The excitation wavelength was 325 nm.
Extended Data Fig. 4 XRD of CN6H [P] thin films.
X-Ray diffraction patterns of CN6H thin films (thickness: 78 nm) on a non-interacting substrate (quartz, black line), 20 nm PTCDA (red) and 100 nm CuI (111) (blue line).
Extended Data Fig. 5 Atomic force microscopy of CN6H thin films.
(a)Atomic force microscopy images of CuI-templated CN6H [M]. The scale bar is indicated and the z-scale is in nm. (b)Atomic force microscopy image of untemplated and templated CN6H [P]. The scale bar is 1 µm. We note that the topography of the neat templating layers has been reported elsewhere, with surfaces of the 100 nm CuI thin films featuring large, pinhole-free smooth grains 30. The neat PTCDA layers are too sticky to successfully image. These types of strong interactions contribute to the broad distribution of supramolecular columns orientations illustrated in Fig. 3.
Extended Data Fig. 6 Planar and cross-sectional view scanning electron microscopy.
The dramatically different morphologies are also apparent in cross-sectional view SEM (a – c): in particular, the smooth surface of the flat-lying supramolecular columns of CuI-templated CN6H and uneven, rough surfaces of PTCDA-templated CN6H. Remarkably, PTCDA-templated CN6H appears to form molecular clusters in domains that extend throughout the entire film thickness, whilst there is some evidence of a layering in the platelet-packing on CuI. The ultra-smooth films of CuI-templated CN6H is responsible for the poor contrast in the planar view SEM.
Extended Data Fig. 7 CN6H [P] 2D GIWAXS Patterns and Simulations.
Experimental and simulated two-dimensional (2D) GIWAXS diffraction patterns of untemplated and templated CN6H [P]. In contrast to CN6H [M], the 1 0 0 reflection of untemplated CH6H [P], has a stronger out-of-plane intensity and the experimentally observed 2D GIWAXS pattern can be replicated by simulating a broad distribution with (1 0 0) planes parallel to the substrate. For PTCDA-templated CH6H [P], the scattering intensity is stronger compared to CN6H [M] but the 2D GIWAXS patterns of both enantiomers can be replicated by simulating a face-on arrangement of supramolecular columns with a reasonably broad distribution of crystallite orientations. CuI-templated CN6H [P] exhibits smaller Bragg spots compared to CN6H [M] but both enantiomers exhibit edge-on orientation and are simulated using the same uniaxial model. We attributed the small differences between CN6H [P] and [M] to experimental variations. Part (f) is repeated from Fig. 3f.
Extended Data Fig. 8 Comparison of powder XRD simulations and Q-dependent 1D profiles.
Azimuthally integrated Q-dependent 1D intensity profiles of untemplated and templated CN6H [M] and CN6H [P], integrated in the range 0.2 Å-1 ≤ Q ≤ 2.2 Å−1 through various χ angles; out-of-plane (in the Qz direction, χ = 0°±20°) and in-plane (which includes all other angles 20° ≤ χ ≤ 90°). The simulated powder XRD from Supplementary Fig. 2 is overlayed and the highest intensity reflections are labelled with the corresponding Miller indices. We attribute the small differences between CN6H [M] and CN6H [P] to experimental variations.
Extended Data Fig. 9 Proposed mechanism for PTCDA templating.
Theoretical molecular electrostatic potential surfaces (a) CN6H and (b) PTCDA calculated using DFT using the B3LYP hybrid functional with the 6-311G(d,p) basis set. The red areas represent electron rich regions of the molecule, whilst the blue areas represent electron poor regions. (c) a cartoon depicting the π-π interactions of flat-lying PTCDA and CN6H.
Extended Data Fig. 10 Proposed mechanism for CuI templating.
(a) Side and top-view of the crystal packing of CuI along the (111) plane, showing the relative positions of the iodine and copper atoms. The surface primarily consists of iodine atoms. (b) and (c) Theoretical molecular electrostatic potential surfaces of CN6H and a cartoon of the electrostatic interactions that force the edge-on configuration of CN6H on CuI.
Source Data Fig. 2
AFM images, UV-Vis/XRD data, Lattice plane diagrams.
Source Data Fig. 3
Experimental and simulated two-dimensional (2D) GIWAXS diffraction patterns of untemplated and templated CN6H [M].
Source Data Fig. 4
Illustrator file of graphic, CD data, molecular structure.
Source Data Extended Data Fig. 1
Unprocessed absorption and fluorescence data.
Source Data Extended Data Fig. 2
Unprocessed absorption and circular dichroism spectra.
Source Data Extended Data Fig. 3
Unprocessed absorption and photoluminescence data.
Source Data Extended Data Fig. 4
Unprocessed XRD data.
Source Data Extended Data Fig. 5
Levelled/background subtracted AFM images.
Source Data Extended Data Fig. 6
Unprocessed cross-sectional and planar SEM images.
Source Data Extended Data Fig. 7
Experimental and simulated two-dimensional (2D) GIWAXS diffraction patterns of untemplated and templated CN6H [P].
Source Data Extended Data Fig. 8
Azimuthally integrated Q-dependent 1D intensity profiles of untemplated and templated CN6H [M] and CN6H [P], integrated in the range 0.2 Å-1 ≤ Q ≤ 2.2 Å-1 through various χ angles; out-of-plane (in the Qz direction, χ = 0°±20°) and in-plane (which includes all other angles 20° ≤ χ ≤ 90°).
Source Data Extended Data Fig. 9
Molecular electrostatic potential surfaces calculated using DFT using the B3LYP hybrid functional at the 6-311 G(d,p) level of theory.
Source Data Extended Data Fig. 10
Crystal packing of CuI along the (111) plane, molecular electrostatic potential surfaces of CN6H.
Rights and permissions
Springer Nature or its licensor holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
About this article
Cite this article
Wade, J., Salerno, F., Kilbride, R.C. et al. Controlling anisotropic properties by manipulating the orientation of chiral small molecules. Nat. Chem. 14, 1383–1389 (2022). https://doi.org/10.1038/s41557-022-01044-6