Photoinduced intramolecular electron-transfer reactions in carbazole-fullerene and phenothiazine-fullerene linked compounds in benzene and benzonitrile as studied by fluorescence, transient absorption, time-resolved EPR, and magnetic field effects

Photoinduced intramolecular electron-transfer reactions in carbazole (Cz)-fullerene (C₆₀) (Cz(8)C₆₀) and phenothiazine (Ph)-C₆₀ (Ph(n)C₆₀ (n = 8, 10, 12)) linked compounds have been investigated in benzene and benzonitrile by fluorescence, transient absorption, and time-resolved electron paramagnetic resonance measurements, and by magnetic field effects on the decay rate constants of the photogenerated biradicals. In benzonitrile, photoinduced intramolecular electron transfer from Cz to the singlet excited state of C₆₀ (¹C₆₀*) occurred in Cz(8)C₆₀, but not to the triplet excited state (³C₆₀*), while the intramolecular electron-transfer to both ¹C₆₀* and ³C₆₀* occurred in Ph(n)C₆₀ (n = 8, 10, 12). In benzene, on the other hand, no electron transfer to both ¹C₆₀* and ³C₆₀* took place in all linked compounds. These results were interpreted in terms of the different Gibbs free energy changes in the two solvents.