Abstract
A novel mechanism of the photochemical reaction of 10-(9H-xanthenylidene)-9(10H)-anthracenone (XA) was proposed on the basis of absorption spectrum canges observed upon photoirradiation, and the temperature effects upon the quantum yields of the radical formation and cyclization reaction. The cyclization reaction of XA has a negative apparent activation energy value (-8.5 kcal/mol), while the radical formation from XA has a positive activation energy value (7.9 kcal/mol). The negative value of the aparent activation energy of the cyclization reaction was explained as a rasult of the competing effect of radical scavenging by oxygen associated with the conformation change which occurs with larger activation energy but smaler steric restriction compared to the cyclization reaction
