Selective photochromism and solvatochromism of a diarylethene with different bridge units

A photochromic diarylethene (1a) with three bis(thien-3-yl) systems, containing a 2,5-dihydrothiophene unit and two imidazole units, has been prepared. 1a shows selective photochromism: upon irradiation with 365 nm, one bis(thien-3-yl) system containing a 2,5-dihydrothiophene unit is selected to undergo photocyclization reaction to form ring-closed isomer 1b, the other two bis(thien-3-yl) systems containing imidazole units are photo-inactive. With 254 nm light irradiation, all three bis(thien-3-yl) systems undergo photocyclization reaction to produce ring-closed isomer 1c. Selective solvatochromism was also observed at a ring-closed state: only 1c showed solvatochromism, and the solvatochromism was dependent on the solvent donor numbers: with the increase of donor numbers of solvent, the absorption of 1c shifted to shorter wavelength.