C-O-bond cleavage of esters with a naphthyl group in the higher triplet excited state during two-color two-laser flash photolysis

摘要

A C-O-bond cleavage of esters having a naphthyl group, NpCOOR and RCO-ONp (Np=alpha and P-naphthyl (Np-alpha and Np-beta, respectively), R= Ph and Me), was found during the two-color two-laser flash photolysis in acetonitrile. The C-O-bond cleavage occurred when NpCO-OR and RCOONp were excited to the singlet excited states (S-1). On the other hand, no reaction occurred from the lowest triplet excited states (T-1). When NpCOOR(T-1) and RCO-ONp(T-1) were excited to the higher triplet excited states (T-n) using the second laser during the two-color two-laser flash photolysis, the C-O-bond cleavage occurred. The C-O-bond cleavage quantum yield (Phi) was estimated from the plots of the Tjstate esters disappeared within a laser flash versus the second laser intensities. The C-O-bond cleavage in (NpCO)-Np-beta-OPh(T-n) occurred more efficiently than in (NpCO)-Np-alpha-OPh(T-n) and that in PhCO-(ONp)-Np-beta(T-n) occurred more efficiently than in PhCO-O Phi Np(T-n). The Phi value for ester with Ph and beta-Np groups was larger than that for ester with Ph and alpha-Np groups. The Phi value for MeCO-(ONp)-Np-alpha(T-n) was similar to those for PhCO-ONp(T-n), while that for MeCO-(ONp)-Np-beta(T-n) was much smaller than those for PhCO-ONp(T-n) and MeCO-(ONp)-Np-alpha(T-n). On the other hand, no C-O-bond cleavage was observed in NpCO-OMe(T-n). The Phi value depended on the characters of the groups (Np, Ph, and Me) on the ester. Whether R is Ph or Me with or without pi electron, respectively, is important for the C-O-bond cleavage. In other words, electronic delocalization of the T, state including Np and ester groups is necessary for the occurrence of the C-O-bond cleavage in NpCO-OR(T-n) and RCO-ONp(T-n).