MOLECULAR DESIGN AND SYNTHESIS OF PHOTOCHROMIC DIARYLETHENES

Although photochromic compounds have potential ability for use in optical memory media, the compounds still await practical applications. The limitation is due to the lack of suitable compounds which fulfill the requirements for the reversible recording media. Among the requirements, more important ones are thermal stability, fatigue resistant property, and sensitivity at diode laser wavelengths (780-830 nm). The present paper proposes a guiding principle for the molecular design of thermally irreversible and fatigue resistant photochromic diarylethenes having the absorption bands at the diode laser wavelengths. According to the principle, more than 20 diarylethenes with heterocyclic rings were synthesized. Among the compounds, 2-(1,2-dimethyl-5-methoxy-3-indolyl)-3-(2-cyano-3,5-dimethyl-4-thienyl) maleic anhydride was found to undergo a thermally irreversible and fatigue resistant photochromic reaction to produce the closed-ring form having an absorption edge extending to 860 nm.