Energy transfer and electron transfer of photoexcited 5,6-open-azaC(60) and 6,6-closed-azaC(60) in the presence of retinyl polyenes: hydrogen-bondingeffect

Photoinduced energy transfer and electron transfer processes via the triple t state of 5,6-open-azaC(60) (2) were compared with those of 6,6-closed-aza C(60) (3) on the basis of kinetic data obtained by means of the transient a bsorption spectra. In nonpolar solvents such as toluene, energy transfer pr edominantly took place from the triplet states of 2 ((T)2*) and 3 ((T)3*) t o retinol and beta -carotene. The rate constant for energy transfer (k(ent) ) from (T)2* to retinol was significant different from that of (T)3*. Furth ermore, on the addition of methanol, the k(ent) value of (T)2* for retinol was decreased, while no change was observed for that of (T)3*. These findin gs suggest that retinol is connected with (T)2* via the hydrogen-bond, but not with (T)3*. The decrease of the k(ent) value of (T)2* by the addition o f methanol suggests that retinol was replaced with methanol. In polar solve nts such as benzonitrile, electron transfer took place from (T)2*/(T)3*; ho wever, the difference in the electron transfer rate between (T)2* and (T)3* was not observed for retinol. This finding implies that the hydrogen-bond between T2* and retinol was not formed in benzonitrile, since retinol was s trongly solvated by the solvent molecules. (C) 2001 Elsevier Science B.V. A ll rights reserved.