Photochromism of new unsymmetrical isomeric diarylethenes bearing a pyridine group

Three new unsymmetrical isomeric diarylethenes having a methoxyl substituent at ortho-, meta-, and para-position of the terminal benzene ring, namely 1-(2,5-dimethyl-3-thienyl)-2-[2-methyl-5-(2-methoxylphenyl)-3-thienyl]perfluorocyclopentene (1o), 1-(2,5-dimethyl-3-thienyl)-2-[2-methyl-5-(3-methoxylphenyl)-3-thienyl]perfluorocyclopentene (2o), and 1-(2,5-dimethyl-3- thienyl)-2-[2-methyl-5-(4-methoxylphenyl)-3-thienyl]perfluorocyclopentene (3o), have been synthesized. The substituent position effect of methoxyl group on their properties, including photochromism and fluorescence both in hexane solution and in PMMA film, and their electrochemical properties, were investigated in detail. These diarylethenes showed good photochromism both in solution and in PMMA film. For the same photochromic diarylethene backbone, the electron- donating methoxyl substituent can effectively depress the cyclization quantum yields and increase the cycloreversion quantum yields compared to those of diarylethenes bearing chlorine atoms reported previously. Diarylethenes 1o–3o showed clear fluorescent switches by photoirradiation both in hexane and in PMMA film. In addition, cyclic voltammetry tests showed that the electron-donating methoxyl group at different position on the terminal benzene ring had a significant effect on the electrochemical properties of these isomeric diarylethenes. Copyright © 2009 John Wiley & Sons, Ltd.