Multiple Effects of Aromatic Substituents on Excited State Properties and Singlet Fission Process in Azaquinodimethane System

Abstract

Singlet fission (SF) could offset thermalization loss of high-energy photons via multiexciton generations, thus holding great potential for improving power conversion efficiency of solar cells. However, the SF-based devices remain basically stagnant so far due to the limited scope of practical SF materials. Therefore, designing and developing practical SF material systems is a imperative but challenging task so far. In this work, we comprehensively investigate the effects of aromatic substituents on excited state properties and SF process in the azaquinodimethane system. The results show that the aromatic substituents have a significant influence on molecular diradical characters and then determine the excited state energetics of SF material system including optical band gaps and triplet energy. Moreover, the aromatic substituents could also influence charge transfer coupling interactions via adjusting molecular packing in aggregate state to shunt the excited state population to exert SF process or trap in excimer species. These outcomes not only offer a deep insight into the multiple regulatory effects of the aromatic substituents on excited state properties and SF process but also provide a practical SF material system, which could lay the foundation for the discovery of new SF-active chromophores and practical applications of new generation light harvesting materials.