Electrostatic repulsion, photogenereated charges

The fourth mechanism (4) invokes the electrostatic repulsion between photogenerated charges as the driving force for conformation changes. Triphenylmethane leucoderivatives (72) have been used as photoreceptor molecules. The chromophore dissociates into an ion-pair under ultraviolet irradiation, generating an intensely green colored triphenylmethyl cation. The cation thermally recombines the counter anion as follows. 

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