Synthesis and photophysical properties of 2,2′-bis(oligothiophene)-9,9′-bifluorenylidene derivatives

Herein, three novel 9,9′-bifluorenylidene derivatives containing thiophenyl, terthiophenyl, and tetrathiophenyl groups at the 2- and 2′-positions of the 9,9′-bifluorenylidene skeleton were synthesized and characterized. Their photophysical and electrochemical properties were investigated systematically. The ground state geometries and electronic distributions of the HOMO and LUMO energy levels of the 9,9′-bifluorenylidene derivatives were calculated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) at the B3LYP/6-31G(d) level.