Intermolecular exciplex formation and photoinduced electron transfer of 1,8-naphthalimide dyads in methylated benzenes

In methylated benzene (MB) solvents, 1,8-naphthalimide (NI) derivatives showed markedly red-shifted emission, which originated from an intermolecular exciplex formation between NI and MB in the singlet excited state. The exciplex emission shifted to longer wavelength according to an increase of the oxidation potential of MB. The Stokes shift of the exciplex emission obeyed Lippert–Mataga theory. On the other hand, the exciplex emission of 1,8-naphthalimide-linker-phenothiazine (NI-L-PTZ) dyads was markedly quenched by the linked PTZ. The transient absorption measurements were carried out to investigate the fast quenching process on NI-L-PTZ dyads in p-XYL/CH3CN. The NI radical ion is predominantly generated from the photoinduced electron transfer (PET) between the singlet excited NI and PTZ. The quantum yields for PET of NI-L-PTZ dyads in p-XYL/CH3CN were smaller than those in pure CH3CN. This indicates that the exciplex formation of NI-L-PTZ dyads with MB competitively occurs with the PET process.