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

NMR and kinetic study of the photochromism of the 3-(2-benzylbenzoyl)-2-ethyl-1-methyl-4(1H)-quinolinone (P0) is reported. Under UV irradiation, two thermally stable but photochemically reversible diastereomeric benzoacridinones (P1 and P2) are formed. Kinetic analysis shows that under UV, all the six possible reversible paths between P0, P1 and P2 are operative, while under visible irradiation, only thermally irreversible photoketonizations from P1 and P2 toward P0 occur. Temperature effects on the P1/P2 ratio and on the rates of photoketonization are evidenced. The presence of thermal activation barriers is assumed to interpret these observations.