UV-Induced Benzyloxy Rotamerization in an Ortho OH-Substituted Aryl Schiff Base

A new benzyloxy containing ortho hydroxyl-substituted aryl Schiff base, trans 2-((2-(benzyloxy)benzylidene) amino)phenol (abbreviated as BBAP), was synthesized and characterized by 1H-, 13C-NMR and infrared spectroscopic techniques and elemental analysis. The conformational landscape of the compound, as well as its infrared spectra in argon and N2 cryogenic matrices (10 K) were investigated, followed by the study of the effects of in situ UV irradiation of the matrix-isolated compound. The structural information was obtained through an extensive series of quantum chemical calculations performed at the DFT(B3LYP)/6-311++G(d,p) level of theory, which enabled to identify 3 low-energy OH···N intramolecularly H-bonded conformers of the molecule that were later found to be present in the as-deposited cryogenic matrices. The 3 experimentally relevant conformers of BBAP differ in the geometry of the benzyloxy substituent, and were discovered to interconvert upon in situ UV irradiation (λ = 230 nm) of the matrix-isolated compound. This is the first report on UV-induced conformational changes taking place in a benzyloxy fragment for a matrix-isolated compound.