Ketyl radical formation of excited 1, 8-naphthalimides in protic polar solvent

Abstract

Photoinduced electron-transfer process of 1,8-naphthalimide-linker-trimethylsilane (NI-O3-TMS, O3 = 3,6,9-trioxaundecyl) and NI-O3 has been investigated using the transient absorption measurements in <TEX>$CH_3CN$</TEX> and <TEX>$CH_3CN/H_2O$</TEX>. The excitation of NI-O3-TMS in <TEX>$CH_3CN$</TEX> produced the NI radical anion (<TEX>$NI^{{\cdot}-}$</TEX>) with a transient absorption band around 413 nm, via the intermolecular electron-transfer between NI moieties in the excited singlet state. In contrast, in a protic polar solvent mixture of <TEX>$CH_3CN/H_2O$</TEX>, a proton abstraction process occurred from <TEX>$NI^{{\cdot}-}$</TEX> to generate the NI ketyl radical (<TEX>$NIH^{\cdot}$</TEX>), which showed a transient absorption band around 405 nm. The decay time constants of <TEX>$NIH^{\cdot}$</TEX> were quite long compared to those of <TEX>$NI^{{\cdot}-}$</TEX> in <TEX>$CH_3CN$</TEX>.