Intermolecular photoinduced electron-transfer of 1,8-naphthalimides in protic polar solvents

Abstract

The intermolecular photoinduced electron transfer (PET) processes of 1,8-naphthalimide (NI) derivatives including NI-linker-phenothiazine dyads were investigated in a protic H₂O/CH₃CN (v/v = 1 : 1) solvent using ns-laser flash photolysis with 355 nm-laser excitation. NI derivatives are surrounded by H₂O in the ground state in H₂O/CH₃CN. The T₁-T_n absorption band of ³NI* was observed at around 470 nm. The transient absorption band at around 410 nm increased concomitantly with the decay of ³NI* in H₂O/CH₃CN. This implies that hydrated NI anion radical (NI˙⁻) is primarily generated via the quenching of ³NI* by NI at the diffusion control rate. This intermolecular PET did not occur in aprotic CH₃CN. The formation and decay times of NI˙⁻ showed strong dependence on the concentration of NI. Then, we suggest that NI˙⁻ could undergo proton abstraction to give ketyl radical species of NI [NI(H)˙] in H₂O/CH₃CN.