Laser multiphoton-gated photochromic reaction of a fulgide derivative

A cycloreversion (ring-opening) process of one of the photochromic fulgide derivatives, 2-[1-(2,5-dimethyl-3-fulyl)-2-methylpropylidenel-3-isopropylidenesuccinic anhydride, was investigated by means of picosecond and femtosecond laser photolysis methods. The drastic enhancement of the reaction yield was observed by the picosecond laser irradiation. On the other hand, the cycloreversion reaction yield under femtosecond laser exposure was almost consistent with the steady-state light irradiation. The excitation intensity effect of the reaction profiles revealed that the successive multiphoton absorption process leading to higher excited states opened the efficient cycloreversion process. The multiphoton-gated reaction for photochromic compounds as diarylethene derivatives was confirmed also for a fulgide derivative. The similarities and differences of the reaction profiles in higher excited states between fulgides and diarylethenes were discussed from the viewpoints of selection rule of optical transition and its dependence on molecular structures.