Substituent position effect on the properties of isomeric photochromic diarylethenes bearing chlorine atoms

Three new isomeric photochromic diarylethenes, namely 1,2-bis[2-methyl-5-(4-chlorophenyl)-3-thienyl]perfluorocyclopentene (1o), 1,2-bis[2-methyl-5-(3-chlorophenyl)-3-thienyl]perfluorocyclopentene (2o), and 1,2-bis[2-methyl-5-(2-chlorophenyl)-3-thienyl]perfluorocyclopentene (3o) which bear two chlorine atoms at the para-, meta-, and ortho-position of both terminal phenyl groups, have been synthesized. The substituent position effect of chlorine atoms on their optoelectronic properties, including photochromic behavior and fluorescence, both in solution and in PMMA amorphous film, and electrochemical properties were investigated in detail. The results elucidated that the chlorine atoms and their substituent positions had a significant effect on the optoelectronic properties of these compounds. These diarylethene derivatives bearing two chlorine atoms have shown good photochromic behavior and fluorescent switching both in solution and in PMMA film. For diarylethenes 1–3, the cycloreversion quantum yields were gradually increased when the chlorine atom was attached to the para-, meta- and ortho-positions of the two terminal benzene rings; but, their absorption maxima, cyclization quantum yields and the molar absorption coefficients both of their open-ring and closed-ring isomers were remarkably decreased one by one. Furthermore, the clear oxidation waves of diarylethenes 1c, 2c and 3c were observed at 1.01, 0.92 and 0.98 V by performing the cyclic voltammograms experiments.