ENHANCEMENT OF REACTIVITY OF THE ESTER CARBONYL GROUP BY INTERCHROMOPHORIC LINKS IN PHOTOCHEMICAL CYCLOADDITIONS - INTERMEDIACY AND ROLES OF PLURAL INTRAMOLECULAR EXCIPLEXES

9-Phenanthrenecarboxylic esters as well as naphthalenecarboxylic ester s linked with p-methoxystyrene derivatives exert an intramolecular com petitive or exclusive oxetane formation through carbonyl addition, alt hough the carbonyl addition is not observed in the corresponding inter molecular systems. The reaction proceeds from the excited singlet stat e involving plural intramolecular exciplexes. The new aspect of carbon yl addition, i.e., the enhancement of reactivity of the ester carbonyl group by interchromophoric links, is discussed on the basis of photoc hemical and photophysical observations as well as MO calculations.