Photophyical and photosensitizing properties of BODIPYs substantially changed by alkyl- and phenyl-amino groups on meso carbon

meso-RNH (R = C3H7, C4H9, PhCH2, H, and Ph) substituted BODIPY compounds have been prepared to examine their photophysical properties and photosensitizing abilities. We have measured the UV-vis absorption, steady state and time resolved fluorescence, excited triplet state formation using laser flash photolysis, singlet oxygen generation ability using chemical trapping method. The results show that the presence of meso-RNH leads to large blue shift of absorption and emission wavelength, remarkable decrease in fluorescence quantum yield and lifetime values, and significant increase in singlet oxygen formation quantum yield. Quantum chemical calculation also reveals the photoinduced charge transfer (PCT) mechanism. We conclude that property changes are due to: 1) S0 and S1 geometry, 2) ground state structural isomerization, and 3) intramolecular PCT. These results and mechanisms are helpful for designing new functional materials.