Photoreversible cyclisation of a 3-(2-benzylbenzoyl)-quinolinone: A highly efficient photochromic compound

Abstract NMR and kinetic study of the photochromism of the 3-(2-benzylbenzoyl)-2-ethyl-1-methyl-4(1H)-quinolinone ( P 0 ) is reported. Under UV irradiation, two thermally stable but photochemically reversible diastereomeric benzoacridinones ( P 1 and P 2 ) are formed. Kinetic analysis shows that under UV, all the six possible reversible paths between P 0 , P 1 and P 2 are operative, while under visible irradiation, only thermally irreversible photoketonizations from P 1 and P 2 toward P 0 occur. Temperature effects on the P 1 / P 2 ratio and on the rates of photoketonization are evidenced. The presence of thermal activation barriers is assumed to interpret these observations.