Electron spin resonance study of the photoreaction of 2,2’,3,3’,5,5’,6,6’-octaphenyl-4, 4’-bi-4h-pyran in tetrahydrofuran

Photodissociation of 2,2’,3,3’,5,5’,6,6’-octaphenyl-4,4’-bi-4H-pyran (D) and recombination of 2,3,5,6-tetraphenylpyranyl radical in tetrahydrofuran solution were investigated by ESR methods. The pattern of the CIDEP signal of the radical indicaess that the photodissociation occurs from the excited singlet state of D. The activatinn energy of the radical recombination was obtained to be 16 ~ 18 kJ/mol. By lowering the temperature of photorrradiatton to -140° C, a radical pair was found to be trapped in the medium and its zero field splitting parameters were determined as | D | = 0.0119 cm-1 and | E | = 0.00050 cm-1.