SYNTHESIS AND PROPERTIES OF PHOTOCHROMIC DIARYLETHENES WITH HETEROCYCLIC ARYL GROUPS

A new class of thermally irreversible and fatigue resistant photochrom ic molecules named diarylethenes has been developed. Theoretical consi deration based on the state correlation diagrams of electrocyclic reac tions revealed that the thermal irreversibility is attained by introdu cing aryl groups that have low aromatic stabilization energy. Accordin g to the molecular design principle thermally irreversible photochromi c diarylethenes having heterocyclic five-membered rings, such as furan , thiophene (or benzothiophene), or thiazole rings, have been newly sy nthesized. Among them, diarylethenes having benzothiophene aryl groups showed an excellent fatigue resistant property. They underwent photoc hromic cycles more than 1.0x10(4) times. The absorption maxima of the closed-ring forms varied from 425 to 828 nm depending on the aryl grou ps, substituents of the aryl groups, and the substitution position of the aryl groups to the ethane moiety. The response times of both cycli zation and ring-opening reactions were less than 10 ps in solution as well as in a crystalline phase. The chemical and thermal control of ph otochromic reactivity was achieved by introducing intramolecular hydro gen 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 crystal s.