Abstract
The acene series, an important class of linearly polycyclic aromatic hydrocarbons, are of interest owing to their unique physicochemical features. With an increase in the number of fused benzene rings, acenes display an evolution of electronic structure and properties. Thus, efforts have been devoted to the synthesis of longer acenes, with dodecacene being the longest acene (12 fused benzene rings) reported to date. However, the formation of polymeric acenes with numerous benzene rings, namely polyacene, has yet to be realized. Herein, we present a methodology for the synthesis of polyacene mediated by a metal–organic framework. Nanoconfined synthesis of precursor polymers in the channels of the metal–organic framework and the subsequent dehydro-aromatization reaction produced polyacene that was overwhelmingly longer than the previously reported acenes. The scalable synthesis of polyacene allowed us to unveil the stability and electronic properties of polyacene, paving the way for their widespread applications in optoelectronic and magnetic devices.

Main
Since the synthesis of pentacene was reported in 1912 (ref. 1), extension of linearly fused benzene rings has attracted research attention because of curiosity around the nature of aromatic molecules and their applications in optoelectronic nanodevices and biological imaging2,3,4,5,6,7,8,9. However, the synthesis of acenes longer than hexacene remains formidably challenging because of their low solubility and chemical instability, as explained by Clar’s sextet theory10. More specifically, this theory explains how increases in the number of non-sextet rings along the acene series endows molecules with an unstable biradical character in their ground state11. Much effort has gone into the synthesis of acenes, and their length has gradually increased (one benzene ring at a time) for many decades. Functionalization with solubilizing and stabilizing substituents has allowed for the preparation of acenes of up to nine fused rings using solution synthesis methods12. The on-surface reaction has also emerged as a promising method to afford unsubstituted acenes under high-vacuum conditions13,14. This methodology has enabled the synthesis of the longest acene yet, one with 12 benzene rings15. However, despite these efforts, polymeric acenes consisting of numerous fused benzene rings, namely polyacene, have not been synthesized.
Using regular nanopores for ship-in-a-bottle synthesis has many advantages, including highly specific reactions in the pores and imposing nanoconfinement effects on reaction selectivity and kinetics16,17,18,19,20,21,22,23,24,25. Recently, metal–organic frameworks (MOFs), which comprise metal ions and organic ligands, have attracted much attention due to their applications in fields such as gas storage, separation, catalysts and drug delivery26,27,28,29,30. One of the characteristic features of MOFs is their structural diversity; their pore size and shape are controllable at the molecular level, providing an ideal compartment for encapsulating a variety of guest species and controlling their assembly structures31,32. The resulting guest molecules can be easily recovered by dissolution of the host frameworks, affording well-defined nanomaterials with accurately controlled structures.
Here, we report the synthesis of polyacene by using a methodology, distinct from conventional methods, grounded on organic and/or surface chemistry. The proposed strategy involves two steps: controlled synthesis of precursor polymers within an MOF and subsequent conversion into polyacene (Fig. 1). The spatial constraints of the MOF allowed for the highly regulated polycoupling reaction of aromatic monomers within the one-dimensional (1-D) nanochannels, providing linearly extended polymeric precursors. Subsequently, the dehydro-aromatization reaction of the precursors provided the bulk quantity of polyacene without any peripheries, which was inaccessible using conventional methods.
An MOF with 1-D nanochannels is used as a reaction template, in which monomers can be aligned along the channel direction. Selective coupling reaction of the monomers at the 3- and 7-position leads to the formation of precursor polymers. The subsequent dehydro-aromatization reaction of the precursor polymers affords polyacene in the bulk scale.
Results and discussion
Hydroacenes, the partially saturated acenes, can be used as precursors of acenes via dehydro-aromatization33. Therefore, we envisioned that polymeric hydroacenes could serve as a precursor for the generation of polyacene. For this purpose, 2,6-bis(bromomethyl)naphthalene (BBMN) and 2,6-bis(bromomethyl)anthracene (BBMA) could be used as monomers if the selective coupling reaction would proceed at the 3- and 7-position. However, targeted precursor polymers were not obtained in the bulk reaction owing to the higher reactivity at zigzag positions than at the 3- and 7-position (Fig. 1 and Supplementary Fig. 1). Thermal treatment of the neat BBMN resulted in the formation of branched and graphitic structures (Supplementary Fig. 2).
To initiate the site-selective polycoupling reaction, an MOF with 1-D nanochannels was used as a host in which the monomers could be aligned along the channel direction. We used [ZrO(L)]n (where L is the dicarboxylate ligand), with 1-D nanochannels along the c-axis, as the host because its pore size can be tuned at the molecular level by changing the dicarboxylate ligand34. Additionally, [ZrO(L)]n has high thermal stability because of the strong coordination bond and high coordination number of the zirconium nodes. On the basis of the molecular dimensions of BBMN (4.9 × 8.5 Å2) and BBMA (4.9 × 11.2 Å2), [ZrO(4,4-biphenyldicarboxylate)]n (1; pore size = 6.9 × 6.9 Å2) was used as a host for the selective propagation of linear polymer chains (Supplementary Fig. 3a). Molecular dynamics (MD) simulations revealed that the accommodated monomers were densely assembled in an end-to-end fashion due to the geometrical constraint and host–guest interactions (Supplementary Fig. 3b,c), which would facilitate the regulated reactions at the 3- and 7-position of the monomers.
Polymerization of the monomers in the nanochannels of 1 was performed as follows. First, the monomers were introduced into the pores of 1 by sublimation to obtain the host–monomer composites (1⊃BBMN and 1⊃BBMA). The monomers were exclusively adsorbed inside the nanochannels, as confirmed by X-ray powder diffraction (XRPD), thermogravimetric (TG) and N2 adsorption measurements (Supplementary Figs. 4–6). Polymerization of BBMN and BBMA was then conducted by heating the composites at 250 °C (below the temperature of monomer release from the pores) for 24 h in a sealed glass tube, resulting in the composites of 1 with poly(naphthalene-2,3:6,7-tetrayl-6,7-dimethylene) (PNTD) and poly(anthracene-2,3:6,7-tetrayl-6,7-dimethylene) (PATD), respectively. We confirmed the formation of the composites (1⊃PNTD and 1⊃PATD) using a series of characterization techniques. XRPD measurements showed that the crystal structure of the host MOF was maintained during the heating process (Supplementary Fig. 4). The morphology and size of the particles of 1 remained unchanged during the polymerization, as confirmed by scanning electron microscopy (Supplementary Fig. 7). These results suggest that polymerization proceeded inside the channels of 1. Furthermore, a drastic decrease in the N2 adsorption capacity of the composites compared with that of the pristine 1 was consistent with the accommodation of the precursor polymers in the nanochannels (Supplementary Fig. 6).
The precursor polymers, PNTD and PATD, were released from the framework of 1 by digesting the host in an aqueous NaOH solution. The complete removal of 1 was confirmed by XRPD (Supplementary Fig. 4) and scanning electron microscopy–energy-dispersive X-ray spectroscopy (Supplementary Fig. 8). We performed structural characterizations of the products using Fourier transform infrared (FTIR), solid-state 13C nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS) measurements. The FTIR spectra of PNTD and PATD display peaks corresponding to the out-of-plane (opla) sp2 C–H vibration mode, which contrast with the product obtained from thermal processing the bulk monomers under the same conditions (Supplementary Figs. 2 and 9), suggesting inhibition of the cross-linking reaction in the MOF channels. Notably, the 13C NMR spectra represent the characteristic signals of the polymeric hydroacenes (Fig. 2a). Formation of the polymers resulted in a complete loss of the bromomethyl group; concomitantly, the appearance of resonance ascribable to the carbon of the methylene group was observed. Additionally, a cluster of peaks, assignable to aromatic carbons35, was observed around 120–140 ppm. In the PNTD spectrum, the peak intensity for the aromatic carbons at the zigzag positions was higher than that of the BBMN heated without the MOF, supporting the progress of site-selective linear polymerization within the 1-D channels of 1 (Supplementary Fig. 10). The peak at 20 ppm was attributed to the methyl terminus of the polymers via the debromination reaction36. The absence of other peaks indicates that the precursor polymers did not undergo any undesired side reactions, such as oxidation and dimerization, during their isolation process. The formation of polymeric compounds was corroborated by the MALDI-TOF-MS spectra, which showed a periodic pattern of signals in agreement with the molecular mass of the repeating unit (Fig. 2b and Supplementary Fig. 11). Remarkably, the precursor polymers consisted of up to several dozens of linearly fused rings, demonstrating the generation of highly extended polymeric hydroacenes mediated by the MOF nanochannels.
a, Solid-state 13C NMR spectra of BBMN, BBMA, PNTD, PATD and polyacene. The coloured circles indicate the signals assigned to sp3carbons of the monomers and precursor polymers. The asterisk (*) corresponds to spinning side bands. b, MALDI-TOF-MS (linear mode) spectra of PNTD (red) and PATD (blue). The orange arrows represent the repeating mass interval of the precursor polymers.
The precursor polymers were transformed into polyacene with numerous benzene rings by heating at 300 °C under air atmosphere. The colour of the samples drastically changed from ochre to dark brown during the heating treatment, suggesting the formation of polyacene with an extended conjugated backbone. In contrast, the transformation reaction did not proceed at all under vacuum conditions, demonstrating that oxygen is essential for the dehydro-aromatization reaction (Supplementary Fig. 12). The obtained polyacene was insoluble in all solvents due to the strong interchain π–π interaction, which may impede microscopic structural analysis; however, the bulk quantity of polyacene meant a wide range of techniques could be used to confirm the conversion of the precursors to polyacene. For instance, solid-state 13C NMR spectroscopy of polyacene did not exhibit the signals for terminal methyl groups of the precursor polymers, presumably because of thermally induced elimination (Fig. 2a). Most strikingly, the methylene resonance peak completely disappeared. The presence of only a broad peak in the aromatic region confirms the formation of polyacene via quantitative dehydro-aromatization reaction7,37. This is also confirmed by the presence of characteristic polyacene peaks in FTIR spectroscopy measurements. The opla aromatic C–H vibration modes are classified as SOLO, DUO, TRIO and QUATRO, in reference to the number of adjacent C–H groups38. Only the SOLO and QUATRO mode were detected at 900 and 736 cm−1, respectively, as was the case with the unsubstituted acene series (Fig. 3a)39,40. The disappearance of the DUO-mode band at approximately 800 cm−1 suggests the removal of the terminal methyl groups in the precursor polymers during the heating process38,39,41, which is consistent with NMR analysis (Fig. 2a).
a, FTIR spectra of tetracene, pentacene, hexacene, heptacene and polyacene synthesized from PNTD and PATD. b, The relative peak area of SOLO to QUATRO vibration modes (ASOLO:AQUATRO) plotted against benzene ring number for the acene series. (black, tetracene; purple, pentacene; sky blue, hexacene; green, heptacene; blue, polyacene from PNTD; red, polyacene from PATD). The mean number of benzene rings in polyacene was evaluated using the correlation between ASOLO:AQUATRO and the number of benzene rings (dotted line). c, Solid-state UV–visible light–near-IR absorption spectra of PNTD, PATD and polyacene. Polyacene is the mixture of extended acenes with a different chain length, giving rise to broad absorption over a wide wavelength, ranging from visible light to near IR, which is in contrast to the previously reported acene series7,44.
We attempted to analyse the polyacene chain length using MALDI-TOF-MS measurements; however, no mass peak corresponding to polyacene was detectable, probably because of its high molecular weight and strong intermolecular interactions which reduced the detection efficiency of polyacene. Therefore, because vibrational spectroscopy is a powerful method for quantitative structural analysis, we analysed polyacene length using IR42,43. The peaks corresponding to the opla sp2 C–H vibration modes (SOLO and QUATRO) of the previously reported acene series were analysed and we found a correlation between those peaks and the number of the benzene rings, demonstrating that the IR analysis is capable of evaluating polyacene length (Supplementary Fig. 13)39. Therefore, several acene molecules with defined structures were synthesized and simulated for IR analysis (Fig. 3 and Supplementary Fig. 14), revealing a linear correlation between the relative peak area of SOLO to QUATRO modes and the benzene ring number. According to the line of best fit, the mean numbers (±S.D.) of benzene rings in polyacene from PNTD and PATD were estimated to be 17.8 ± 3.3 and 18.6 ± 3.5, respectively (Fig. 3b). Additionally, the absorption spectra of polyacene corroborated the presence of acenes with numerous fused benzene rings. The S0 to S1 transition band of acenes (p band) shifts bathochromically with increasing size of the acene system44,45. The polyacene exhibited substantial absorption bands in the near-IR region (Fig. 3c). The bandgaps of polyacene from PNTD and PATD were estimated to be 1.30 and 1.28 eV, respectively, on the basis of the absorbance onsets, which were notably small enough to be comparable with the theoretical limit value (1.23 eV) for acenes with infinite chain length44. Also, given that the precursor polymers consisted of up to several dozen rings (Fig. 2b and Supplementary Fig. 11), these results indicate that, to our knowledge, the polyacene obtained in this study is the longest among the acene series reported so far.
The unprecedented length of the generated polyacene incentivized our efforts to unveil its physicochemical properties. The study on the structural stability of polyacene produced remarkable results. It is well known that longer acenes are more susceptible to oxidation and dimerization reactions because of their inherent singlet biradical character46,47. However, the 13C NMR spectra of polyacene did not show the peaks for sp3-bridgehead carbons37 and carbonyl groups generated by these reactions (Fig. 2a). Therefore, we concluded that such unfavourable reactions did not take place in the bulk polyacene; therefore, we evaluated the biradical character of polyacene using electron spin resonance (ESR) and superconducting quantum interfering device (SQUID). In the ESR spectrum of polyacene, we observed a signal with a g value of 2.003, ascribable to a carbon-centred radical (Fig. 4a and Supplementary Fig. 15a)48. SQUID polyacene data revealed a fitting component with a steep decrease in the magnetic susceptibility upon cooling from 70 to 20 K, in accordance with the Bleaney–Bowers equation (Supplementary Fig. 15b)49. This magnetic behaviour is typical for open-shell singlet biradical molecules50; therefore, these results suggested that polyacene did have a biradical nature, which is in agreement with theoretical calculations51,52,53. This is also supported by the NMR polyacene analysis: we detected NMR signals that were broader than those of the precursors which were ascribed to a thermally populated paramagnetic triplet biradical (Fig. 2a)48.
a, ESR spectrum of polyacene synthesized from PATD. No hyperfine splitting was observed, suggesting the delocalization of spin density along the polymer chains. b, Temperature dependence of the magnetic susceptibility χ (grey circle) of polyacene prepared from PATD. The magnetic susceptibility plots could be fitted to the sum (black line) of Curie–Weiss (blue line) and Bleaney–Bowers (red line) equations. The singlet–triplet energy gap (ΔES–T) of polyacene was calculated to be −0.0024 eV by the Bleaney–Bowers equation, which is smaller than the theoretical value for polyacene with infinite chain length50, probably due to the intermolecular spin–spin interaction in the bulk state51.
To identify the mechanisms underlying the unexpectedly high stability of polyacene, the biradical species were quantitatively analysed by ESR. The spin concentration of polyacene was calculated to be approximately 1 × 1018 spins g−1 (Fig. 4a). Notably, this value is several orders of magnitude smaller than that predicted from the length of polyacene54. A similar reduction in radical nature has been reported for several π-conjugated radical molecules that form π-dimers in the solid state. The intermolecular antiferromagnetic interactions result in these molecules being undetectable via ESR55. The insolubility of polyacene in all solvents implied strong interchain interactions; therefore, the aggregation of polyacene was studied using MD simulations, and the π-stacked structure was energetically most stable (Supplementary Fig. 16a). The aggregation structure was also revealed by XRPD of the polyacene sample, showing a peak corresponding to π–π stacking (Supplementary Fig. 16b). The observed broad diffraction peak suggested the presence of the stacked structures with non-uniform interchain distance, as shown in the MD structure of polyacene. Therefore, it is probable that interchain antiferromagnetic coupling occurs when in close proximity, giving rise to the decrease in the inherent biradical character of polyacene56,57.
We evaluated the composition of polyacene using X-ray photoelectron spectroscopy by initially focusing on the surface of the polyacene particles. The C1s core level region displays peaks corresponding to the oxidized carbon (Supplementary Fig. 17). The surface of the polyacene particles was etched using argon plasma to examine the inner composition, which led to a drastic decrease in the oxidized carbon peaks. We observed a small NMR peak, assignable to the oxidized carbons (Supplementary Fig. 18), when polyacene was left in air for a long period (>30 days). These results suggest that the oxidation reaction took place only near the surface of the polyacene particles owing to their biradical character. The high stability of the bulk polyacene was also confirmed by TG analysis, which showed no weight loss up to 350 °C (Supplementary Fig. 19a). The FTIR spectra of polyacene before and after heating up to 350 °C displayed no obvious changes, and the opla sp2 C–H vibration modes were clearly observable, indicating its high thermal stability (Supplementary Fig. 19b). Again, this behaviour was in sharp contrast to that of acenes in solution, which readily decompose via oxidation and/or dimerization reactions. Therefore, the unexpectedly high stability of polyacene in the solid state can be attributed to the chain aggregation that decreased its biradical character, limited oxygen access to the polymer chains and restricted the chain motion required for undesirable oxidation and dimerization reactions7,11,37,39,58,59.
Conclusions
Unsubstituted acenes have thus far been fabricated on surfaces under ultrahigh vacuum conditions because of their unstable zigzag edges15,60, presenting a barrier to their scalability. Here, we used an MOF to demonstrate the bulk-scale synthesis of polyacenes with exceptional length. The physicochemical properties of the acene series depending on benzene ring number led to the development of theoretical arguments45,61,62. Our findings represent an important step toward not only unveiling the unique topological properties of the acene series63,64 but also its future applications in various areas, including molecular electronics, optoelectronics and spintronics. For example, polyacene, being a mixture of polymeric chains with different lengths, is capable of absorbing light over a wide wavelength, ranging from visible to near IR (Fig. 3c). Along with its remarkably high stability, this light-absorbing feature would be beneficial for applications in photoenergy conversion systems.
Methods
Synthesis of precursor polymers in 1
The general procedure for synthesis was as follows: Degassed 1 was prepared by heating it at 160 °C for 12 h in a vacuum. BBMN (298 mg) and degassed 1 (1,000 mg) were mixed in a round-bottom flask (20 ml) and heated at 150 °C for 1 h under reduced pressure, leading to vapour adsorption of BBMN throughout the internal and external surface of 1. The externally absorbed monomer was selectively removed by heating at 150 °C for 12 h under vacuum, affording a composite of 1 including BBMN (1⊃BBMN, 1,237 mg). The amount of BBMN adsorbed in the composite was calculated to be 18.7%, as determined by TG measurements. 1⊃BBMN was then heated at 250 °C in a sealed reaction container for 24 h to perform polymerization, resulting in 1 and PNTD nanocomposite (1⊃PNTD, 1,124 mg). PATD was synthesized identically within the nanochannels from BBMA (loading amount of BBMA was 33.5%).
Isolation of precursor polymers from 1
1⊃PNTD (1,680 mg) was stirred in a 1 M aqueous solution of NaOH (120 ml) for 24 h, followed by washing three times with a 5% v/v aqueous solution of HF (20 ml) for complete decomposition of the host framework. The collected PNTD was washed with CHCl3 and then dried under reduced pressure to obtain PNTD (123 mg, 70% yield based on the loading amount of BBMN in 1⊃BBMN). PATD was isolated from 1 in a similar manner (39% yield).
Conversion from PNTD and PATD to polyacene
The precursor polymers, PNTD (48 mg) and PATD (24 mg), were heated at 300 °C under air for 24 h to obtain polyacene of 38 and 18 mg, respectively.
Reporting summary
Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article.
Data availability
The data supporting the findings of this study are available within the article and its Supplementary Information. Source data are provided with this paper.
References
Mills, W. H. & Mills, M. CCXXX.—The synthetical production of derivatives of dinaphthanthracene. J. Chem. Soc. Trans. 101, 2194–2208 (1912).
Congreve, D. N. et al. External quantum efficiency above 100% in a singlet-exciton-fission-based organic photovoltaic cell. Science 340, 334–337 (2013).
Anthony, J. E. Functionalized acenes and heteroacenes for organic electronics. Chem. Rev. 106, 5028–5048 (2006).
Lee, D. et al. In vivo imaging of hydrogen peroxide with chemiluminescent nanoparticles. Nat. Mater. 6, 765–769 (2007).
Tateishi, K. et al. Room temperature hyperpolarization of nuclear spins in bulk. Proc. Natl Acad. Sci. USA 111, 7527–7530 (2014).
Tönshoff, C. & Bettinger, H. F. Pushing the limits of acene chemistry: the recent surge of large acenes. Chem. Eur. J. 27, 3193–3212 (2021).
Watanabe, M. et al. The synthesis, crystal structure and charge-transport properties of hexacene. Nat. Chem. 4, 574–578 (2012).
Yue, W., Suraru, S.-L., Bialas, D., Müller, M. & Würthner, F. Synthesis and properties of a new class of fully conjugated azahexacene analogues. Angew. Chem. Int. Ed. 53, 6159–6162 (2014).
Liang, Z., Tang, Q., Xu, J. & Miao, Q. Soluble and stable N-heteropentacenes with high field-effect mobility. Adv. Mater. 23, 1535–1539 (2011).
Clar, E. Polycyclic Hydrocarbons (Academic Press,1964).
Müller, M., Ahrens, L., Brosius, V., Freudenberg, J. & Bunz, U. H. F. Unusual stabilization of larger acenes and heteroacenes. J. Mater. Chem. C 7, 14011–14034 (2019).
Kaur, I., Jazdzyk, M., Stein, N. N., Prusevich, P. & Miller, G. P. Design, synthesis, and characterization of a persistent nonacene derivative. J. Am. Chem. Soc. 132, 1261–1263 (2010).
Urgel, J. I. et al. On-surface light-induced generation of higher acenes and elucidation of their open-shell character. Nat. Commun. 10, 861 (2019).
Krüger, J. et al. Tetracene formation by on-surface reduction. ACS Nano. 10, 4538–4542 (2016).
Eisenhut, F. et al. Dodecacene generated on surface: reopening of the energy gap. ACS Nano. 14, 1011–1017 (2020).
Schmidt, B. V. K. J. Metal-organic frameworks in polymer science: polymerization catalysis, polymerization environment, and hybrid materials. Macromol. Rapid Commun. 41, 1900333 (2020).
Kitao, T., Zhang, Y., Kitagawa, S., Wang, B. & Uemura, T. Hybridization of MOFs and polymers. Chem. Soc. Rev. 46, 3108–3133 (2017).
Ding, N. et al. Partitioning MOF-5 into confined and hydrophobic compartments for carbon capture under humid conditions. J. Am. Chem. Soc. 138, 10100–10103 (2016).
Distefano, G., Comotti, A., Bracco, S., Beretta, M. & Sozzani, P. Porous dipeptide crystals as polymerization nanoreactors. Angew. Chem. Int. Ed. 51, 9258–9262 (2012).
Comotti, A. et al. Confined polymerization in highly ordered mesoporous organosilicas. Chem. Eur. J. 21, 18209–18217 (2015).
Wu, C. G. & Bein, T. Conducting carbon wires in ordered, nanometer-sized channels. Science 266, 1013–1015 (1994).
Lee, H. C. et al. Toward ultimate control of radical polymerization: functionalized metal–organic frameworks as a robust environment for metal-catalyzed polymerizations. Chem. Mater. 30, 2983–2994 (2018).
Uemura, T., Ono, Y., Kitagawa, K. & Kitagawa, S. Radical polymerization of vinyl monomers in porous coordination polymers: nanochannel size effects on reactivity, molecular weight, and stereostructure. Macromolecules 41, 87–94 (2008).
MacLean, M. W. A. et al. Unraveling inter‐ and intrachain electronics in polythiophene assemblies mediated by coordination nanospaces. Angew. Chem. Int. Ed. 55, 708–713 (2016).
Mulzer, C. R. et al. Superior charge storage and power density of a conducting polymer-modified covalent organic framework. ACS Cent. Sci. 2, 667–673 (2016).
Furukawa, H., Cordova, K. E., O’Keeffe, M. & Yaghi, O. M. The chemistry and applications of metal-organic frameworks. Science 341, 2130444 (2013).
Kitagawa, S., Kitaura, R. & Noro, S. Functional porous coordination polymers. Angew. Chem. Int. Ed. 43, 2334–2375 (2004).
Horcajada, P. et al. Porous metal-organic-framework nanoscale carriers as a potential platform for drug delivery and imaging. Nat. Mater. 9, 172–178 (2010).
Sumida, K. et al. Carbon dioxide capture in metal-organic frameworks. Chem. Rev. 112, 724–781 (2012).
Lee, J. et al. Metal-organic framework materials as catalysts. Chem. Soc. Rev. 38, 1450–1459 (2009).
Kitaura, R. et al. Formation of a one-dimensional array of oxygen in a microporous metal-organic solid. Science 298, 2358–2361 (2002).
Talin, A. A. et al. Tunable electrical conductivity in metal-organic framework thin-film devices. Science 343, 66–69 (2014).
Zuzak, R. et al. Higher acenes by on-surface dehydrogenation: from heptacene to undecacene. Angew. Chem. Int. Ed. 57, 10500–10505 (2018).
Guillerm, V. et al. A series of isoreticular, highly stable, porous zirconium oxide based metal-organic frameworks. Angew. Chem. Int. Ed. 51, 9267–9271 (2012).
Dorel, R., McGonigal, P. R. & Echavarren, A. M. Hydroacenes made easy by gold(I) catalysis. Angew. Chem. Int. Ed. 55, 11120–11123 (2016).
Guan, B. T. et al. Methylation of arenes via Ni-catalyzed aryl C-O/F activation. Chem. Commun. (Camb.) (12), 1437–1439 (2008).
Einholz, R. et al. Heptacene: characterization in solution, in the solid state, and in films. J. Am. Chem. Soc. 139, 4435–4442 (2017).
Centrone, A. et al. Structure of new carbonaceous materials: the role of vibrational spectroscopy. Carbon 43, 1593–1609 (2005).
Jančařík, A. et al. Preparative-scale synthesis of nonacene. Nat. Commun. 13, 223 (2022).
Mondal, R. et al. Synthesis, stability, and photochemistry of pentacene, hexacene, and heptacene: a matrix isolation study. J. Am. Chem. Soc. 131, 14281–14289 (2009).
Yamada, Y. et al. Carbon materials with zigzag and armchair edges. ACS Appl. Mater. Interfaces 10, 40710–40739 (2018).
Ţucureanu, V., Matei, A. & Avram, A. M. FTIR spectroscopy for carbon family study. Crit. Rev. Anal. Chem. 46, 502–520 (2016).
Sasaki, T., Yamada, Y. & Sato, S. Quantitative analysis of zigzag and armchair edges on carbon materials with and without pentagons using infrared spectroscopy. Anal. Chem. 90, 10724–10731 (2018).
Shen, B., Tatchen, J., Sanchez-Garcia, E. & Bettinger, H. F. Evolution of the optical gap in the acene series: undecacene. Angew. Chem. Int. Ed. 57, 10506–10509 (2018).
Korytár, R. et al. Signature of the Dirac cone in the properties of linear oligoacenes. Nat. Commun. 5, 5000 (2014).
Bendikov, M. et al. Oligoacenes: theoretical prediction of open-shell singlet diradical ground states. J. Am. Chem. Soc. 126, 7416–7417 (2004).
Zade, S. S. & Bendikov, M. Reactivity of acenes: mechanisms and dependence on acene length. J. Phys. Org. Chem. 25, 452–461 (2012).
Huang, R. et al. Higher order π-conjugated polycyclic hydrocarbons with open-shell singlet ground state: nonazethrene versus nonacene. J. Am. Chem. Soc. 138, 10323–10330 (2016).
Bleaney, B. & Bowers, K. D. Anomalous paramagnetism of copper acetate. Proc. R. Soc. A 214, 451–465 (1952).
Dressler, J. J. et al. Thiophene and its sulfur inhibit indenoindenodibenzothiophene diradicals from low-energy lying thermal triplets. Nat. Chem. 10, 1134–1140 (2018).
Hachmann, J., Dorando, J. J., Aviles, M. & Chan, G. K. L. The radical character of the acenes: a density matrix renormalization group study. J. Chem. Phys. 127, 134309 (2007).
Qu, Z., Zhang, D., Liu, C. & Jiang, Y. Open-shell ground state of polyacenes: a valence bond study. J. Phys. Chem. A 113, 7909–7914 (2009).
Barker, J. E. et al. Molecule isomerism modulates the diradical properties of stable singlet diradicaloids. J. Am. Chem. Soc. 142, 1548–1555 (2020).
Trinquier, G., David, G. & Malrieu, J. P. Qualitative views on the polyradical character of long acenes. J. Phys. Chem. A 122, 6926–6933 (2018).
Fukui, K. et al. Electronic structure of a stable phenalenyl radical in crystalline state as studied by SQUID measurements, cw-ESR, and 13C CP/MAS NMR spectroscopy. Synth. Met. 103, 2257–2258 (1999).
Xiang, Q. et al. Stable olympicenyl radicals and their π-dimers. J. Am. Chem. Soc. 142, 11022–11031 (2020).
Sato, H. et al. Drastic effect of water-adsorption on the magnetism of carbon nanomagnets. Solid State Commun. 125, 641–645 (2003).
Miura, T., Kitao, T. & Uemura, T. Nanoconfinement of an otherwise useless fluorophore in metal–organic frameworks to elicit and tune emission. J. Phys. Chem. C 126, 6628–6636 (2022).
Hayashi, H. et al. Visible-light-induced heptacene generation under ambient conditions: utilization of single-crystal interior as an isolated reaction site. Chem. Eur. J. 26, 15079–15083 (2020).
Mishra, S. et al. Large magnetic exchange coupling in rhombus-shaped nanographenes with zigzag periphery. Nat. Chem. 13, 581–586 (2021).
Schmitteckert, P., Thomale, R., Korytár, R. & Evers, F. Incommensurate quantum-size oscillations in acene-based molecular wires—effects of quantum fluctuations. J. Chem. Phys. 146, 092320 (2017).
Miao, Y. et al. Mechanism of length-induced magnetism in polyacene molecules. Phys. Rev. B 105, 094419 (2022).
Karakonstantakis, G., Liu, L., Thomale, R. & Kivelson, S. A. Correlations and renormalization of the electron-phonon coupling in the honeycomb Hubbard ladder and superconductivity in polyacene. Phys. Rev. B 88, 224512 (2013).
Ulbricht, R. et al. Carrier dynamics in semiconductors studied with time-resolved terahertz spectroscopy. Rev. Mod. Phys. 83, 543–586 (2011).
Acknowledgements
This work was supported by the Japan Science and Technology CREST (JPMJCR20T3) and PRESTO (JPMJPR21A7) programmes, and a Grant-in-Aid for Scientific Research (JP21H01738 and JP21H05473) from the Ministry of Education, Culture, Sports, Science and Technology, Government of Japan. We appreciate the fruitful discussions with M. Koshino, T. Kubo and T. Kawakami from Osaka University.
Author information
Authors and Affiliations
Contributions
T.U. conceived of and directed the project. T.K. and T.M. designed and performed the experiments. T.U. codesigned the experiments. Y.T. and S.S. contributed to ESR measurements. R.N. and T.H. assisted with SQUID measurements. Y.S.C., H.H. and H.Y. synthesized the precursor molecules of hexacene and heptacene. T.K., T.M. and T.U. wrote the manuscript, with input from all the co-authors.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Peer review
Peer review information
Nature Synthesis thanks Dan Zhao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Alison Stoddart, in collaboration with the Nature Synthesis team.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Source data
Source Data Fig. 2
13C NMR and MALDI-TOF-MS data.
Source Data Fig. 3
FTIR and UV–visible–near-IR spectroscopy data.
Source Data Fig. 4
ESR and SQUID data.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Kitao, T., Miura, T., Nakayama, R. et al. Synthesis of polyacene by using a metal–organic framework. Nat. Synth 2, 848–854 (2023). https://doi.org/10.1038/s44160-023-00310-w
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s44160-023-00310-w
This article is cited by
-
MOF-made polyacenes
Nature Synthesis (2023)