Synergistic effect of trimethylsilane for photoinduced electron transfer on 1,8-naphthalimides in polar solvent

Photoinduced electron-transfer (PET) process of 1,8-naphthalimide-linker-TMS (NI-SOS-TMS, where SOS = dithiaoxaundecyl and TMS = trimethylsilane) has been investigated using transient absorption measurements in CH3CN and CH3CN/H2O (v/v = 9:1). The femtosecond pulsed laser excitation of NI-SOS-TMS produced the NI radical anion (NI center dot-) with a transient absorption band around 415 nm, via the intramolecular PET from heteroatom nearby TMS to NI in the singlet excited (S-1) state. However, in case of NI-SOS, the transient band at around 415 nm increased concomitantly with the decay of (NI)-N-1* (or (NI)-N-3*) at around 470 nm. This is implied that NI center dot- is primarily generated via the intermolecular quenching of (NI)-N-1* (or (NI)-N-3*) by NI. In contrast, in a protic polar solvent mixture of CH3CN/H2O, a proton abstraction process occurred from NI center dot- to generate the NI ketyl radical (NIH center dot), which showed a transient absorption band around 405 nm. The decay time constants of NIH center dot were quite long compared to those of NI center dot- in CH3CN. Both the rates of charge transfer and deactivation processes of transient species largely depended on the protic polar solvent.