Optical kinetic spectroscopy is used to investigate the triplet state properties of solution phase fullerenes. These triplet states, which are the molecules' lowest-energy and longest-lived electronic excitations, show lifetimes and absorption spectra that vary from fullerene to fullerene. In room temperature toluene solution, the intrinsic triplet lifetime of C₇₀ exceeds that of C₆₀ by a factor at of least 80. The 'self-quenching' deactivation of triplet states through encounters with ground state molecules occurs with rate constants of 1.6 X 10⁷⁰ M^-1s^-1 for C₆₀ and 3 X 10⁷ M^-1s^-1 for C₇₀. In solutions containing mixtures of fullerenes, transfer of triplet excitation between species is efficient and reversible, with rate constants up to 2 X 10⁹ M^-1s^-1. When C₆₀ is aliphatically derivatized at two adjacent sites to form (6,6)-closed dihydrofullerene structure, intrinsic triplet lifetimes are shortened by more than a factor of 3 to approximately 45 microsecond(s) . The triplet spectra of these compounds, in which the derivitizing groups are not sterically strained, are very similar to each other but significantly different from the C₆₀ spectrum. The (6,6)-closed epoxide, C₆₀O, displays unusual triplet state behavior. Its initial triplet spectrum is distinct from that of the other derivatives studied and decays in approximately 6 microsecond(s) through nonexponential kinetics. Evolution of the induced spectrum suggest the possibility of epoxide ring opening form the triplet state of C₆₀O.

Date Published: 1 November 1997
PDF: 10 pages
Proc. SPIE 3142, Fullerenes and Photonics IV, (1 November 1997); doi: 10.1117/12.279253

Published in SPIE Proceedings Vol. 3142:
Fullerenes and Photonics IV
Zakya H. Kafafi, Editor(s)