Synthesis and optoelectronic properties of unsymmetrical isomeric diarylethene derivatives having a fluorine atom

Three unsymmetrical diarylethene compounds bearing a fluorine atom at either ortho-, meta-, or para-positions of the terminal phenyl ring, namely 1-(2,5-dimethyl-3-thienyl)-2-[2-methyl-5-(2-fluorophenyl)-3-thienyl]perfluorocyclopentene (1o), 1-(2,5-dimethyl-3-thienyl)-2-[2-methyl-5-(3-fluorophenyl)-3-thienyl]perfluorocyclopentene (2o), and 1-(2,5-dimethyl-3-thienyl)-2-[2-methyl-5-(4-fluorophenyl)-3-thienyl]perfluorocyclopentene (3o), have been synthesized. Their structures were determined by single-crystal X-ray diffraction analysis. The fluorine atom position effect on their properties, such as photochromism, fluorescence, and their electrochemical properties, were investigated in detail. The results elucidated that the fluorine atom and its substituted position had a significant effect on the optoelectronic properties of these compounds. For diarylethenes 1–3, the ortho-substituted derivative 1 had the biggest cyclization and cycloreversion quantum yields; while the meta-substituted derivative 2 showed the biggest extinction coefficient and the absorption maxima both in hexane and in PMMA film. The emission peaks of diarylethenes 1o–3o displayed an increasing trend along with the fluorine atom from the ortho- to meta- to the para-position of substitution both in hexane and in PMMA film, but their intensities showed a reverse changing trend. The oxidation waves of diarylethenes 1c–3c were clearly observed at 1.44, 1.27 and 1.42 V by performing the cyclic voltammograms, and those of 1o–3o were observed at 1.29, 1.12 and 1.41, respectively.