Photophysics and Photochemistry of Trifluoromethylfullerene Fluorophores

Five fluorescent trifluoromethyl fullerenes have been studied using time-resolved and steady-state spectroscopy. Prior to this study Nakamura et al. reported the highest quantum yield for a fullerene derivative of 0.24 with the molecule C₆₀Ph₁₀(CH₂Ph)₃Me₂H (1). Three of the trifluoromethyl fullerenes presented exceed this, and one isomer of C₇₀(CF₃)₁₀ has a quantum yield of 0.68 (2). The fluorescence lifetimes of three C₇₀(CF₃)₁₀ compounds has been measured using time-resolved fluorescence spectroscopy. The compound with the highest quantum yield also has the longest fluorescence lifetime 51 ns. The ability of these compounds to sensitize the production of singlet oxygen has also been investigated.

Between isomers of C₇₀(CF₃)₈ and C₇₀(CF₃)₁₀ only one CF₃ group is in a different location. This change in position results in 200 and 14-fold increases in the quantum yield. These isomers have very similar size and location of the remaining pi system; the remaining pi system had previously been hypothesized to be the determining factor for fluorescence quantum yields of C₆₀ derivatives (1,3). Instead we propose that fluorescence quantum yields are more related to the oscillator strength and Δ_S1−T1 energy gaps. These values can be predicted using time-dependent density functional theory calculations, which provides a method to target the most fluorescent fullerene derivatives.

References

1. T. Fujita; Y. Matsuo; and E. Nakamura, Chem. Mater., 24, 3972 (2012).

2. K. P. Castro; Y. Jin; J. J. Rack; S. H. Strauss; O. V. Boltalina; A. A. Popov, J. Phys. Chem. Lett., 4, 2500 (2013).

3. Y. Matsuo; Y. Sato; M. Hashiguchi; K. Matsuo; and E. Nakamura, Adv. Funct. Mater., 19, 2224 (2009).