The effect of the fluorine atom position upon isomeric photochromic diarylethenes bearing a pyrrole unit

A new class of isomeric diarylethenes bearing a pyrrole moiety have been synthesized, and their properties including photochromism, fluorescence, and electrochemical properties have been discussed systematically. Each of the diarylethenes exhibited evident photochromism and functioned as a remarkable fluorescent switch in both solution and PMMA films. Their photoconversion ratios were larger than 90%, and the fluorescent modulation efficiencies were greater than 88% in the photostationary state. The absorption maxima, quantum yields of cyclization and cycloreversion, and band-gaps of the closed-ring isomers increased whereas the emission intensity and band-gaps of the open-ring isomers greatly decreased when the fluorine atom was attached at any of the three positions on the terminal benzene ring. Cyclic voltammograms suggested that the oxidation onsets and band-gaps of the open-ring isomers were much bigger than those of the closed-ring isomers. The fluorine atom and its substituted position could availably modulate their optical and electrochemical behaviors.