Photophysical and electron-transfer properties of mono- and multiple-functionalized fullerene derivatives

Mono- and multiple-functionalized C-60 derivatives were synthesized and stu died for their photophysical properties. Electronic absorption spectra and absorptivities of the C-60 derivatives in solution were measured and compar ed. By recording the fluorescence spectra using a near-infrared-sensitive e mission spectrometer, we quantitatively determined fluorescence quantum yie lds of the C-60 derivatives. For the mono-functionalized CBD derivatives, t he compound with a [5,6]-open fulleroid addition pattern on the fullerene c age appeared to be considerably less fluorescent than those with a [6,6]-cl osed cage addition pattern. Despite the disturbance of the electronic struc ture via multiple additions to the fullerene cage, the multiple-functionali zed C-60 derivatives exhibited no dramatic changes in fluorescence quantum yields in comparison with the mono-functionalized C-60 derivatives. The flu orescence lifetimes of the C-60 derivatives, obtained using the time-correl ated single photon-counting technique, were all in the range of 1-3 ns. In addition, the dependencies of the fluorescence intensities and lifetimes of the C-60 derivatives on the concentration of the quencher N,N-diethylanili ne (DEA) were evaluated. Apparently, upon photoexcitation, even the C-60 de rivatives with a hexa-functionalized fullerene cage underwent significant e lectron-transfer interactions with the electron donor DEA, resulting in eff icient fluorescence quenching. In a polar solvent, the contribution of stat ic quenching also became important, The results for different derivatives a nd their molecular structural and mechanistic significance are discussed.