The reversible photocyclization of 1, 2-diarylethene derivatives having methyl-substituted heterocyclic rings has been found to constitute a photochromic system, which is both thermally irreversible and fatigue resistant. cis-1, 2-Dicyano-l, 2-bis (2, 4, 5-trimethyl-3- thienyl) ethene (3d) undergoes a photocyclization to produce the dihydro derivative of benzodithiophene (4d) with A, at 512 nm, which is stable for more than 12 h at 80" C. The ...
