Excited States of Fulgides

The general formula for fulgides is represented as compound 1. Based on the absorption spectra data, 1-3 fulgide systems can be separated into two largely independent cinnamic anhydride-type chromophores. Freudenberg eta/.101 studied the absorption spectra of ethyl /rans-cinnamate 82 and diethyl-(E,E)-bisbenzylidene succinate 83 and found that the absorption spectrum of compound 83 was similar to that of compound 82, rather than 1,4-diphenylbutadiene. This indicated that compound 83 had two relatively independent chromophores, which was supported by Heller and Szewczyk.16 They demonstrated that the UV spectrum of (E,E)-bis-(a-phenylethylidene) succinic anhydride It was almost identical with a 1 1 mixture of (E,Z) and (E,E) isomers of the same fulgide. 

Kurita et al. 2 Takeda et al. 3 and Parthenopoulos and Rentzepis11 used picosecond laser photolysis techniques to study the photochromic processes of furyl fulgide. They found that the excited states of furyl fulgide and its colored form were singlet states and had n,n characteristics. Takeda et al.13 reported from theoretical studies that the values of the oscillator strength and the radiation lifetime (/r) were 

6 x lo-2 and 14 ns, respectively. The decay time t of the luminescence of the colored form of the fulgide was about 1-2 ns according to the experimental data. The values of the decay time were a function of the luminescence photon energy for various concentrations. The results suggested that the nonradiative tunneling process from the excited state to the ground state was responsible for the decay. 

Is the excited state of fulgimide different from that of fulgide No more studies have been presented to date. 

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