THERMALLY IRREVERSIBLE PHOTOCHROMIC SYSTEMS - REVERSIBLE PHOTOCYCLIZATION OF 1,2-DISELENENYLETHENE AND 1,2-DIINDOLYLETHENE DERIVATIVES

Diarylethene derivatives with selenophene or indole rings were synthesized in an attempt to obtain thermally stable photochromic compounds having the absorption bands at longer wavelengths and to confirm our previous theoretical prediction for molecular design of thermally irreversible photochromic compounds. The absorption maxima of the closed-ring forms of 2,3-bis(2,4,5-trimethyl-3-selenenyl)maleic anhydride (6) and 2,3-bis(l,2-dimethyl-3-indolyl)maleic anhydride (10) were observed at 565 and 620 nm, respectively. Although dicyano and maleic anhydride derivatives with selenophene rings showed thermally irreversible photochromic reactions with a relatively high quantum yield (0.3), the derivatives with indole rings underwent thermal ring-opening reactions in the dark. The closed-ring forms of the derivatives with selenophene rings kept the absorption intensity constant for more than 12 h at 80°C, while the absorption intensity of the closed-ring form of the maleic anhydride derivative with indole rings decreased to 50% of the initial intensity in 3 h at 80°C. The difference in thermal stability between the diarylethenes with selenophene and indole rings was interpreted by the difference in aromatic stabilization energy of the two rings, as predicted by our previous report, rather than a steric effect. © 1990, American Chemical Society. All rights reserved.