Synthesis and Properties of Photochromic Diarylethenes with Heterocyclic Aryl Groups

Abstract

Abstract A new class of thermally irreversible and fatigue resistant photochromic molecules named diarylethenes has been developed. Theoretical consideration based on the state correlation diagrams of electrocyclic reactions revealed that the thermal irreversibility is attained by introducing aryl groups that have low aromatic stabilization energy. According to the molecular design principle thermally irreversible photochromic diarylethenes having heterocyclic five-membered rings, such as furan, thiophene (or benzothiophene), or thiazole rings, have been newly synthesized. Among them, diarylethenes having benzothiophene aryl groups showed an excellent fatigue resistant property. They underwent photochromic cycles more than 1.0 × 104 times. The absorption maxima of the closed-ring forms varied from 425 to 828 nm depending on the aryl groups, substituents of the aryl groups, and the substitution position of the aryl groups to the ethane moiety. The response times of both cyclization and ring-opening reactions were less than 10 ps in solution as well as in a crystalline phase. The chemical and thermal control of photochromic reactivity was achieved by introducing intramolecular hydrogen bonding groups or oligothiophene aryl groups to the diarylethenes. Some of the dithienylperfluorocyclopentene derivatives were found to show photochromic reactivity in the crystalline phase. The reactivity was dependent on the conformation and molecular packing in the crystals.