Synthesis of Novel Photochromic Films by Oxidation Polymerization of Diarylethenes Containing Phenol Groups

We report the synthesis of some diarylethene derivatives attached to phenol moieties, which show remarkable photochromic reactions. A dithienylethene group attached to the o‐phenol moiety (1,2‐bis[2,4‐dimethyl‐5‐(o‐hydroxyphenyl)‐3‐thienyl]hexafluorocyclopentene) was polymerized according to Hay's method; the resulting film was insoluble to any solvents, and showed no absorption band attributable OH group in its IR spectrum. Isomeric dithienylethenes attached to m‐ and p‐phenol moieties did not form films under the same oxidation conditions, but instead formed films by copolymerization with 4,4′‐dihydroxyphenyl ether. Although the homopolymer film and copolymer films showed reversible photochromic reactions by alternate irradiation with UV and visible light, the coloration was not remarkable. Polymerization of closed‐ring isomers of the dithienylethenes did not give pre‐polymers and instead decomposed, while the closed‐ring isomer of a bisbenzothienylethene derivative attached to the o‐phenol moiety (1,2‐bis[2‐methyl‐6‐(o‐hydroxyphenyl)‐1‐benzothiophen‐3‐yl]hexafluorocyclopentene) formed a polymer film by the same procedure. This polymer film showed a remarkable photochromic reaction, indicating the photo‐reactive conformation was fixed in polymer matrix, and X‐ray diffraction measurements show that the film is in the amorphous phase. The photochromic reaction can also be monitored by IR spectroscopy, making it applicable for non‐destructive read‐out recording films. Photochromic polymer films, on which the non‐destructive readout of an image using infrared light has been successfully shown, have been prepared. The films are formed by oxidation polymerization of diarylethenes and a derivative containing benzothiophene rings attached to phenol moieties, which form a film (see Figure) whilst retaining the photoreactive anti‐parallel conformation.