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

Abstract

The photophysical properties of two C 70 (CF 3 ) 8 and three C 70 (CF 3 ) 10 isomers were studied using steady-state and time-resolved absorption and fluorescence spectroscopy. Four of the compounds exhibited quantum yields (Φ F ) higher than for any C 70 derivative reported to date, and three exceeded 0.24, the highest Φ F reported for any fullerene or fullerene derivative. A difference in the location of only one CF 3 group in C 70 (CF 3 ) 8 and C 70 (CF 3 ) 10 isomers resulted in 200-fold and 14-fold increases in Φ F, respectively. The isomer of C 70 (CF 3 ) 10 with the highest Φ F (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 S 1 state in one of the C 70 (CF 3 ) 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 C 70 (CF 3 ) n derivatives.