Photochromic reactions of bis(2-thienyl) perfluorocyclopentenes

Photochromic reactivities and the absorption maxima of dithienylethenes were found to depend on the connecting position of the thiophene rings to the ethene moiety. When thiophene rigns are connected at 2-position, the absorption maxima of the open-ring form showed bathochromic shifts. Substitution of aromatic rings to the 5 and 5'-positions of the thienyl rings shifted the absorption band of the open-ring form to a longer wavelength and decreased the cyclization quantum yield. When 4-(N,N-diethylamino) phenyl rings were used as the aryl groups, the photochromic reaction was not observed. By the addition of acid, photo-reactivity was recovered. The photogenerated closed-ring form has the absorption at a shorter wavelength than the open-ring form.