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.