Single crystals of charge-transfer (CT) complexes composed of the polyaromatic hydrocarbon, coronene, as an electron donor (D) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) analogues as electron acceptor (A) were obtained. Elucidation of crystal structures of CT complexes enables a systematic investigation of dynamic properties of coronene molecules lying in different types of crystalline environments. Solid-state 2 H NMR spectra of CT complexes formed with deuterated coronene confirmed the in-plane 6-fold flipping motion of the coronene molecules. The dihedral angle between adjacent coronene and TCNQ analogue within the DA-type alternating π-column is closely correlated with the dynamic properties, such as rotational rate and activation energy. Side-by-side intermolecular hydrogen-bonding also seems to have an effect in ways that lead to the suppressed rotation. These findings would provide an initial step toward the selection, design, and engineering of counter components of supramolecular rotators in the CT solids.

In this study, we obtained the first cation radical solid of a highly symmetric (D6h) polyaromatic hydrocarbon, coronene, by electrooxidation. The (coronene)3Mo6Cl14 salt, which is formed with an Oh‐symmetric molybdenum cluster unit Mo6Cl142–, has an isotropic cubic structure with Pm$\bar {3}$m symmetry. The presence of two orientations for the coronene molecules related by an in‐plane 90° rotation (merohedral disorder) allows for fourfold symmetry along the <100> direction. The disorder has dynamic features because 2H NMR spectroscopic studies revealed that the coronene molecules undergo an in‐plane flipping motion. The observation of two motional sites with significantly different rotational rates (300 Hz and 5 MHz at 103 K) in an approximate 2:1 ratio appears to be consistent with the splitting of a Raman‐active A1g mode, confirming a random charge‐disproportionated state instead of a uniform partially‐charged state. The slower‐ and faster‐rotating species are assigned to charge‐rich and charge‐poor coronenes, respectively, with respect to C–H···Cl hydrogen bonds with neighboring Mo6Cl142– cluster units. The electrical conductivity of the salt is rather high but is well‐described by a three‐dimensional (3D) variable‐range hopping mechanism, which is possibly associated with the random charge disproportionation. These results provide a significant step forward in developing an isotropic 3D π‐conducting system composed of planar π‐conjugated molecules.

Coronene, which is the smallest D6h -symmetric polycyclic aromatic hydrocarbon, attracts particular attention as a basic component of electronic materials because it is the smallest fragment of graphene. However, carrier generation by physical methods, such as photo- or electric field-effect, has barely been studied, primarily because of the poor π-conduction pathway in pristine coronene solid. In this work we have developed unprecedented π-stacking columns of cationic coronene molecules by electrochemical hole-doping with polyoxometallate dianions. The face-to-face π-π interactions as well as the partially charged state lead to electrical conductivity at room temperature of up to 3 S cm(-1) , which is more than 10 orders of magnitude higher than that of pristine coronene solid. Additionally, the robust π-π interactions strongly suppress the in-plane rotation of the coronene molecules, which has allowed the first direct observation of the static Jahn-Teller distortion of cationic coronene molecules.

A charge-transfer (CT)-type supramolecular rotor, (coronene) 2 F 4 TCNQ, was obtained by vacuum cosublimation. The CT complex has an unprecedented crystal structure consisting only of DDA-type alternating π-columns of coronene (D) and electron acceptor (A), and coronene molecules with a pronounced undulating structure form no C−H···F hydrogen bonds with adjacent F 4 TCNQ molecules in the side-by-side direction. These structural features are in contrast with those reported for (coronene)F 4 TCNQ that has DA-type alternating π-columns, which was obtained by diffusion in dichloromethane/pentane. Coronene molecules in the present complex undergo an in-plane rotation in the gigahertz region at 233 K, which is 3 orders of magnitude faster than that in (coronene)F 4 TCNQ. Furthermore, the activation energy for the rotation was found to be about half of the value reported for (coronene)F 4 TCNQ. These results clearly demonstrate that dynamic properties of the assemblies (CT complexes) can be varied by changing the assembly method (crystallization method), even when the parts (molecules) used as rotator and stator components are the same.

Recent developments in the arena of charge-transfer complexes composed of the D 6h-symmetric polycyclic aromatic hydrocarbon, coronene, are highlighted with emphasis on the structural and physical properties of these complexes. Because of the dual electron-donating and -accepting abilities of coronene, this group involves structurally-defined four cation salts and three anion salts. The Jahn-Teller distortions and in-plane motion of coronene molecules in the solids, both of which are closely associated with the high symmetry of coronene molecules, and syntheses of clathrate-type complexes are also presented.