Photorotamerization of methyl salicylate and related compounds in cryogenic matrices

Spectroscopic studies of methyl salicylate (MS), salicylamide (SAM), and o-hydroxyacetophenone (OHAP) isolated in 12 K matrices of, variously, SF{sub 6}, Ar, Kr, or Xe are presented. Irradiation in the S{sub 1} electronic absorption bands of the normal intramolecularly hydrogen bonded conformers generates matrix-stabilized rotamers. Ground-state photorotamer conformations deduced from infrared spectra are correlated with steady-state electronic absorption, excitation, and emission spectra, as well as with emission lifetime data. Matrix-isolated SAM and OHAP photolyze to yield phosphorescent, nonintramolecularly hydrogen bonded rotamers via photochemically reversible pathways. In contrast, irradiation of MS in SF{sub 6} proceeds via a photochemically irreversible pathway to generate a rotamer with a weak intramolecular hydrogen bond between the phenol hydrogen and the methoxy oxygen of the ester moiety. The MS photorotamer exhibits both UV fluorescence and visible phosphorescence.