Heptagon-Fusion as a Molecular Design Strategy for Distorted Acenes

Abstract

Distorted acenes have attracted considerable attention owing to their 3-D structures and curvature-dependent properties, which are being used to develop novel organic functional materials. Herein, we report a series of diphenylene-fused acene derivatives incorporating doubly heptagon-fused structures. The introduced heptagons induced two stable conformations, twisted and saddle forms, to the acene cores. Kinetic analyses revealed that the isomerization barrier between the twisted and saddle forms increased with increasing acene length. The twisted isomers exhibited red-shifted absorption spectra compared to the corresponding saddle isomers. Quantum chemical calculations suggest that the narrower band gaps of the twisted isomers primarily originate from the smaller HOMO-LUMO gaps of the twisted acene cores compared with those of the saddle acene cores. These results not only provide a new design strategy for distorted acenes but also provide insights into their unique properties.