Photochromism of asymmetrical diarylethenes with a pyrimidine unit: Synthesis and substituent effects

Abstract Five photochromic diarylethenes with a six-membered pyrimidine moiety were synthesized to investigate the effects of the substituents on their photochromic behaviors, and the structures of four of the diarylethenes were determined by single-crystal X-ray diffraction analysis. The pyrimidine moiety was connected directly to the central cyclopentene ring as an aryl moiety to participate the photoisomerization reaction in solution, solid amorphous films, and crystalline phase. All of the diarylethene derivatives showed favorable photochromism and functioned as notable fluorescent photo-switches in both solution and solid media. The electron-donating substituents enhanced their cyclization quantum yields, fatigue resistance, and fluorescence quantum yields, whereas the electron-withdrawing groups exerted inversed actions on the diarylethenes. The results revealed that the pyrimidine moiety and substituents played a very important role during the process of photoisomerization reactions.