LAUSR

Abstract Two quinazolinone-based Schiff's bases ( 1 and 2 ) have been studied by UV/vis, EPR, and NMR spectroscopic methods, as well as DFT calculations. UV/vis spectroscopy confirmed that both compounds undergo significant changes upon UV irradiation in DMSO solutions in the presence of molecular oxygen. EPR spectroscopy proved generation of reactive radical intermediates via the interaction of activated molecular oxygen with the solvent molecules upon UV irradiation. Furthermore, photochemically-induced electron transfer led to isomerization from anti to syn -isomer when irradiated by UV light as demonstrated by NMR spectroscopy. The process is relatively slow, the isomerization takes up to 6 h and the conversion reaches about 40%. The original equilibrium was re-established within 30 days. Theoretical and experimental data also showed that the degree of conversion and the rotational energy barriers are affected by substitution at the aromatic rings.