Journal of Physical Chemistry A, Vol.109, No.21, 4713-4720, 2005
Photoinduced charge separation and charge recombination in [60]fullerene-ethylcarbazole and [60]fullerene-triphenylamines in polar solvents
Molecules of C-60 covalently connected with N-ethylcarbazole (EtCz) and triphenylamine (TPA) have been synthesized. Photoinduced electron transfer in C-60-EtCz and C-60-TPA has been studied in polar and nonpolar solvents using time-resolved transient absorption and fluorescence measurements. From the fluorescence lifetimes, the excited singlet state of the C-60 moiety (C-1(60)*) of C-60-TPA generates predominantly C-60(center dot-)- TPA(center dot+), which decays quickly to the ground state within 6 ns even in polar solvents. In the case of C-60-EtCz, on the other hand, about half of the C-1(60)* moiety generates short-lived C-60(center dot-)-EtCz(center dot+), while the other half of the C-1(60)* moiety is transferred to the C-3(60)* moiety via intersystem crossing in dimethylformamide, in which the energy level of C-60(center dot-)-EtCz(center dot-) is lower than that of C-3(60)*. Thus, the charge separation takes place via C-3(60)* generating C-60(center dot-)-EtCz(center dot+), having a lifetime as long as 300 ns, probably because of the triplet spin character of C-60(center dot-)-EtCz(center dot+). A special property of the EtCz moiety to stabilize the hole in the charge-separated state was revealed.