IR induced cis↔trans isomerization of 2-naphthol: Catalytic role of hydrogen-bond in the photoinduced isomerization

Abstract

An infrared laser induced cis↔trans isomerization has been investigated for 2-naphthol and its hydrogen(H)-bonded cluster with NH3 in the S1 electronic state by UV–IR double resonance excitation in a supersonic jet. A specific isomer was pumped to a X–H (X=O, C or N) stretching vibration in S1 by a sequential UV–IR two-photon excitation, and the resultant product species were analyzed by dispersing their fluorescence. It was found that the IR excitation induces the isomerization for the H-bonded cluster with the excitation less than 3000 cm−1, while no isomerization was found to occur for bare 2NpOH even with an input energy of 3610 cm−1. The substantial reduction of the isomerization barrier height represents evidence of the catalytic nature of H-bonding in the conformational isomerization. It was also found that the isomerization efficiency is very high at low IR frequency and exhibits a marked IR frequency dependence.