A Revisit to the Orthogonal Bodipy Dimers: Experimental Evidence for the Symmetry Breaking Charge Transfer-Induced Intersystem Crossing

Abstract

A series of Bodipy dimers with orthogonal conformation were prepared. The photophysical properties were studied with steady-state and time-resolved transient spectroscopies. We found the triplet-state quantum yield is highly dependent on the solvent polarity in the orthogonally linked symmetric Bodipy dimers, and the intersystem crossing (ISC) is efficient in solvents with moderate polarity. The photoinduced symmetry-breaking charge transfer (SBCT) in polar solvents was confirmed by femtosecond transient absorption spectroscopy, with the charge separation (CS) kinetics on the order of a few picoseconds and the charge recombination (CR) process occurring on the nanosecond time scale in dichloromethane. These observations are supported by the calculation of the charge separated state (CSS) energy levels, which are high in nonpolar solvents, and lower in polar solvents, thus the CR-induced ISC has the largest driven force in solvents with moderate polarity. These results clarify the mechanism of SOCT-ISC in ...