Isostructural Charge-Transfer Cocrystals Based on Triptycene End-Capped Quinoxalinophenanthrophenazine

Abstract

Charge transfer (CT) crystals of an electron donor and an acceptor have electronic properties that are different from the two pure components. Despite the great potential of such CT crystals have for organic electronics, the control of the spatial arrangement of donor and acceptor molecules in the cocrystals plays a crucial role for the charge transfer itself or, for example, for charge transport. In most cases, by changing e.g. the acceptor components, various cocrystals are accessible but in almost all cases with different packing motifs and thus crystallographic parameters. This makes a direct and systematic comparison of different donor–acceptor pairs difficult or even impossible. On the basis of a triptycene end-capped dimethoxy-quinoxalinophenanthrophenazine (QPP-OMe) as a donor with six small electron-deficient molecules as acceptors, an isostructural packing could be realized, where the QPP-OMe donor is forming voids with nearly the same orientation and size to enclathrate the acceptor molecules, as has been revealed by single-crystal X-ray diffraction. The CT complexes were studied spectroscopically, supported by density functional theory calculations.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

“…The group also reported charge-transfer (CT) complexes based on 155.6c with six small electron-deficient molecules. 309 …”

“…The formation of π-dimers occurred to a different degree in all crystal structures, showing that the directing capability of the triptycene end capping was also pronounced in the presence of larger aromatic substituents that could disturb the packing by competing π-stacking interactions (e.g., in 155.8c ). The group also reported charge-transfer (CT) complexes based on 155.6c with six small electron-deficient molecules …”

Two Dimensional Triptycene End‐Capping and Its Influence on the Self‐Assembly of Quinoxalinophenanthrophenazines†

“…[ 27 ] However, when only one triptycene end‐cap is attached to QPPs, precise π‐dimerization occurred in the solid state, mostly independent from further substituents at the backbone. [ 28‐31 ] Especially the latter observation is interesting to finally develop a crystal engineering synthon for controlling the orientation of π‐stacking.…”

Influence of Internal Molecular Motions in the Photothermal Conversion Effect of Charge-Transfer Cocrystals

“…Organic charge-transfer (CT) cocrystals are a type of crystalline materials recently employed in the construction of novel optoelectronic devices. , CT cocrystals might exhibit highly attractive properties and have been used in ambipolar transport, as optical waveguides, , or in broadband photodetection, thanks to their tunable photoluminescence (PL). − The intermolecular CT phenomena in cocrystals arise from strong π–π interactions between donor and acceptor components. Such species are usually planar, conjugated molecules that, upon association, produce a distinct crystalline array, with new emissive features. − The significant orbital overlap between the donor and acceptor components in a cocrystal promotes changes in the energies of the frontier molecular orbitals (FMOs), resulting in a narrowed energy gap that drastically modifies the photophysical features of a CT cocrystal, opening the way to new properties, like PTC. , …”