Perfluoroalkyl [70]-Fullerenes as Robust Highly-Luminescent Fluorocarbons, or Position of One CF₃ Group Matters

The photophysical properties of two C70(CF3)8 and three C70(CF3)10 isomers were studied using steady-state and time-resolved absorption and fluorescence spectroscopy. Four of the compounds exhibited quantum yields (ΦF) higher than for any C70 derivative reported to date, and three exceeded 0.24, the highest ΦF reported for any fullerene or fullerene derivative. A difference in the location of only one CF3 group in C70(CF3)8 and C70(CF3)10 isomers resulted in 200-fold and 14-fold increases in ΦF, respectively. The isomer of C70(CF3)10 with the highest ΦF (0.68 in toluene) also exhibited the longest fluorescence lifetime, 51 ns, thus competing favorably in its luminescent properties with the most luminescent carbon materials studied to date. Formation of the S1 state in one of the C70(CF3)10 isomers occurred within 0.6 ps and its nanosecond-long decay was monitored by ultrafast transient absorption spectroscopy. Time-dependent density functional theory calculations were performed to provide a physically meaningful understanding of the photophysical properties of C70(CF3)n derivatives.