ISOTOPE AND TEMPERATURE EFFECTS IN ULTRAFAST PROTON-TRANSFER FROM A STRONG EXCITED-STATE ACID

The introduction of naphthol derivatives that exhibit excited-state ac idities comparable to strong mineral acids, has opened the way for dir ect investigation of ultrafast proton-transfer in aqueous solutions an d alcohols. We report on the direct measurement of the isotope and tem perature effects on 5-cyano-1-naphthol excited-state proton dissociati on in the full composition range of water-methanol mixtures. The resul ts indicate that in pure water the proton-transfer rate is almost acti vationless in the proton coordinate and is mainly controlled by the so lvent. In pure methanol the reaction shows down considerably and is ma inly controlled by activation along the proton coordinate.