Substituent effects on ultrafast excited-state proton transfer of protonated aniline derivatives in aqueous solution

Abstract

Substituent effects on the proton dissociation of protonated aniline derivatives upon femtosecond laser pulse excitation are investigated for m- and p-cyanoanilines and m- and p-methoxyanilines in aqueous solution. The cyano substitution at the meta-position increases the rate significantly ( k dis=3.7 × 10 11 s −1) compared to aniline ( k dis=1.3 × 10 10 s −1), while the methoxy substitution reduces the rate remarkably. Either substituent at the para-position shows only slight influences on the rate. The strong dependences of the k dis value on the substituent and the substituted position are reasonably explained on the basis of the free energy change.