Excited states and reduced and oxidized forms of C-76(D-2) and C-78(C-2v')

The singlet and triplet excited state properties of C-76(D-2) and C-78(C-v') have been investigated using picosecond laser flash photolysis and pulse radiolysis. Both C-76 and C-78 are weakly fluorescent as they undergo internal nonradiative conversion and intersystem crossing to generate a triplet excited state. Unlike their predecessor, C-60, the excited larger fullerenes have structured spectral bands in the visible/NIR region. The triplet excited states of C-76 and C-78 were also generated independently by energy transfer from triplet excited biphenyl with a diffusion-controlled rate (k(et) approximate to 1 x 10(10) s(-1)). These larger fullerenes readily undergo one-electron reduction and oxidation by reacting with radiolytically generated (CH3)(2)C-.(OH) and (CH2Cl2)(.+) radicals. The absorption features of excited states and chemical reactivity of C-76 and C-78 are compared with those of C-60, C-70, and C-84. The characterization of radical anions of these larger fullerenes is also made with complementary reduction experiments with UV-irradiated TiO2 nanoparticles.