The effect of substituent position upon unsymmetrical isomeric diarylethenes bearing a methoxy group

Three unsymmetrical isomeric photochromic diarylethenes bearing a methoxy group at either the para-, meta- or ortho-positions on one terminal benzene ring were synthesized and their optical and electrochemical properties investigated. Each of the compounds exhibited high photo-reactive sensitivity and functioned as a fluorescent photo-switch both in solution and in PMMA film. The molar absorption coefficients of both of the open-ring and closed-ring isomers decreased when the methoxy group was attached at any of the three positions on the terminal benzene ring whereas the cycloreversion quantum yield gradually increased in going from the para- to meta- to the ortho-position of substitution. Oxidation waves were clearly observed at 0.55, 0.74 and 0.58 V from cyclic voltammograms for some compounds but not for others at these voltages.