Triarylmethane leuco-form

As an example of conformational change induced by the introduction of electric charges along a macromolecule, let us consider the polymer (15) which in its side chains carries triarylmethane groups in their leuco-form (15). Upon photoirradiation this neutral group dissociates into triphenylmethyl cation and hydroxyl anion. The polymer chain of the irradiated sample adopts an expanded conformation to alleviate the unfavorable ionic interactions between adjacent cations. These changes are reflected by a marked increase in solution viscosity upon photoirradiation in aqueous or methanolic solutions of a polyacrylamide with side chains of structure (15). The viscosity recovers its initial value when irradiation is discontinued. 

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