Experimental and Theoretical Studies of the Photoisomerization Mechanisms

It was reported that the picosecond formation and nanosecond decay of a transient absorption were produced by irradiation of frans-stilbene in solvent [48, 49]. This transient was referred to as the p state. The p state lifetime rapidly decreased in solvents of increasing polarity [50]. It was suggested to be the zwitterionic character of the p state, that is, the formation of a diphenylmethyl anion tethered to diphe-nylmethyl cation. 

The role of central bond torsion in nonvertical triplet excitation transfer to stilbenes, an example of stilbene analogues, biindanylidenes, was recently discussed 

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