Substituent and solvent effects on photoexcited states of functionalized fullerene[60]

Steady-state absorption/fluorescence spectra and time-resolved absorption/fluorescence spectra were measured to investigate the photoexcited states properties of N-methylpyrrolidinofullerenes C₆₀[(C₃H₆N)R] [R = H (1), p-C₆H₄CHO (2), p-C₆H₄NO₂ (3), p-C₆H₄OMe (4), p-C₆H₄NMe₂ (5)]. Functionalization causes bandshifts to longer wavelength for absorption and fluorescence spectra, accompanied by enhancements in the fluorescence quantum yields in nonpolar solvents. The triplet (T) states of these derivatives show very similar properties (quantum yields, molar absorption coefficients and O₂ quenching) to C₆₀ whereas T-T absorption bands shift to short wavelength and the lowest triplet energies decrease compared with those of C₆₀. Derivative 5, which has a strong electron-donating group, shows a prominent solvent polarity effect on the fluorescent quantum yield and lifetime, and triplet formation, suggesting that intramolecular charge transfer takes place.