Photochemistry of 1- and 2-Naphthols and Their Water Clusters: The Role of 1 ππ*(La ) Mediated Hydrogen Transfer to Carbon Atoms

Abstract

The computational analysis of the isomer- and conformer-dependent photochemistry of 1- and 2-naphthols and their microsolvated water clusters is motivated by their very different excited state reactivities. We present evidence that 1- and 2-naphthol follow distinct excited state deactivation pathways. The deactivation of 2-naphthols, 2-naphthol water clusters, as well as of the anti conformer of 1-naphthol is mediated by the optically dark ¹ πσ* state. The dynamics of the ¹ πσ* surface leads to the homolytic cleavage of the OH bond. On the contrary, the excited state deactivation of syn 1-naphthol and 1-naphthol water clusters follows an uncommon reaction pathway. Upon excitation to the bright ¹ ππ*(L_a ) state, a highly specific excited state hydrogen transfer (ESHT) to carbon atoms C8 and C5 takes place, yielding 1,8- and 1,5-naphthoquinone methides. The ESHT pathway arises from the intrinsic electronic properties of the ¹ ππ*(L_a ) state of 1-naphthols.

Keywords: excited state hydrogen transfer; hydrogen/deuterium exchange; naphthols; photochemistry; water clusters.