A photoresponsive molecular switch. Reaction of COz and epoxide regulated by aluminum porphyrin-stilbazole system

A novel example of a ‘photoresponsive molecular switch’, the light-driven on-off switching system for chemical reaction, composed of aluminum porphyrin and stilbazole is found to regulate the reaction of carbon dioxide and propylene oxide to give propylene carbonate. The reaction is catalyzed by aluminum porphyrin through the photoisomerization of stilbazole. In the dark, the reaction of carbon dioxide and propylene oxide to give propylene carbonate proceeds very slowly for the methoxyaluminum porphyrin trans-stilbazole system. However, the reaction was accelerated by UV light (A = 290 360 nm), but less so by visible light (A > 380 nm). INTRODUCTION Photoresponsive chemical systems are essential to biological functions, such as vision (ref. 1) and photomorphogenesis in plants (ref. 2), and have attracted continuous interests in connection with mimicing such natural photoresponsive systems in order to construct artificial systems. Chemists trying to elucidate the mechanism of photoresponsive natural systems have devoted their efforts to investigation of the physico-chamical properties of light-absorbing molecules, such as photochromism and electron-transfer. However, they have hardly dealt with connecting these properties with biosynthetic chemical reactions to eventually afford the products of the processes induced by photoresponsive molecules. On the other hand, interest in artificial svtems which exhibit functions in =