Crystals of a diarylethene with a perfluorocyclohexene ring exhibit a remarkable photosalient effect upon UV light irradiation that is attributed to the structural changes that occur when going from open- to closed-ring isomers in the crystalline state, together with the existence of two conformers with different photoconversions compared with those of a perfluorocyclopentene derivative. Our current results give a design principle for molecular structures so as to achieve the photosalient effect for photochromic crystals.

Photochromic diarylethene derivatives bearing hydrophilic N,N-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)sulfonamide (SO₂NTEG₂) (1–3) or myo-inositol (4–6) substituents were synthesized. Although the solubility in aqueous solution of the derivatives containing the four tri(ethylene glycol) chains was relatively poor, the solubility was improved by introducing two myo-inositol residues. The derivatives could be dissolved even in pure water and underwent photochromism upon alternate irradiation with ultraviolet (UV) and visible light, in both organic and aqueous solutions. The absorption maxima of the open- and closed-ring isomers of these derivatives and the photostationary conversion ratios from the open- to the closed-ring isomers upon UV irradiation did not change much, even when the solvent polarity was changed. These results indicate that the diarylethene derivatives are mono-molecularly dissolved in aqueous solution and that intermolecular interactions between the derivatives are negligible when the concentration is less than 1×10⁻⁴ mol⋅L⁻¹.