Photochromism of new unsymmetrical diarylethenes based on the hybrid of azaindole and thiophene moieties

Abstract

A new class of photochromic diarylethenes with both azaindole and thiophene moieties were synthesized to investigate the effects of the substituents on their photochromic behaviors, and their structures were determined by single crystal X-ray diffraction analysis. The azaindole moiety was connected directly to the central cyclopentene ring as a heteroaryl moiety to participate the photoisomerization reaction in solution, solid amorphous films, and the single crystalline phase. Each of the diarylethenes exhibited remarkable fluorescent photo-switches in both solution and solid media. The electron-donating substituents significantly enhanced their cyclization quantum yields, while the electron-withdrawing groups greatly increased the molar absorption coefficient of their closed-ring isomers. Cyclic voltammetry studies indicated that the band-gaps of diarylethenes with an azaindole notably increased when going from electron-donating substituents to electron-withdrawing substituents. The results revealed that the azaindole moiety and substituents played a vital role in the process of photoisomerization reactions for these diarylethenes.