Furan Substitution and Ring Fusion Strategies for Enhancing the Fluorescence Performance of Oligothiophene

Oligothiophenes have attracted a lot of attention due to their excellent photoelectric properties. However, the effects of ring fusion and furan substitution on the optoelectrical properties of oligothiophenes are still unclear. In this study, based on popular pentathiophene, eight molecules including three ring-fused and five furan-substituted derivatives are systematically designed, and their frontier molecular orbitals, dipole moments, planarity, exciton binding energy (E_b), singlet-triplet energy differences, and fluorescence quantum yields are calculated. The computed data demonstrate that full-ring fusion and two- and more-furan substitutions can greatly enhance the fluorescence quantum yields. Five potential molecules with about 100% of fluorescence quantum yield, i.e., TTTTT, SOSOS, OSOSO, SOOOS, and OOOOO, are screened. The results show that to obtain high fluorescence quantum yield, high E_b is required, and the flexible torsional displacement during the excitation from ground to the first excited state should be removed as much as possible. This work sheds some light on the future design of high-performance oligothiophene-based fluorescent materials.