Solvent effects on triplet–triplet annihilation upconversion kinetics of perylene with a Bodipy-phenyl-C60 photosensitizer

Abstract

The solvent effect usually plays an important role in triplet–triplet annihilation (TTA) upconversion processes. In this work, we have studied the TTA upconversion kinetics of perylene with Bodipy-phenyl-C₆₀ as the triplet photosensitizer in five solvents, 1,4-dioxane, dichlorobenzene, chlorobenzene, toluene, and tetrahydrofuran (THF). Although no significant solvent effect was observed in steady-state absorption and fluorescence emission spectra, the overall TTA upconversion quantum yields showed a profound dependence on solvent properties, i.e. 4.9% in 1,4-dioxane, 7.1% in dichlorobenzene, 6.7% in chlorobenzene, 4.6% in toluene, and 2.2% in THF (the maximum of 50%). Each elementary reaction step involved in the overall process was analyzed by applying femtosecond and nanosecond time-resolved transient absorption spectroscopy, revealing that the fluorescence emission of perylene was more significantly affected by the solvents in contrast to the other steps. Moreover, an extra intramolecular energy-transfer pathway of Bodipy-phenyl-C₆₀ was found via the formation of charge-separated states in dichlorobenzene, chlorobenzene, and THF solvents, once being excited. These conclusions provide valuable clues to choose the most favorable solvent for the higher TTA upconversion efficiency in related applications.