Photochromism of two novel protoncontrollable isomeric diarylethenes with a pyridine moiety: substituent effects on their properties

Two novel hybrid isomeric diarylethenes with pyridine and pyrrole units have been synthesized by a parallel reaction, and their structures were determined by single-crystal X-ray diffraction analysis. They exhibited distinctly different photochromic behavior and fluorescent properties upon photoirradiation due to the different substituent effects. In the crystalline phase, one is photoactive with an anti-parallel conformation, while the other is non-photoactive with a parallel conformation. Moreover, the closed-ring isomers showed different acidichromism in dichloromethane. The absorption maxima of one showed extraordinarily large red shifts of 120 nm, whereas that of the other exhibited extraordinarily large blue shifts of 194 nm.

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