A new class of photochromic compounds exemplified by E-5-dicyanomethylene-4-(dialkyl and dicycloalkyl)methylene[1-(2,5-methyl-3-furyl) and (2-methyl-5-phenyl-3-thienyl)ethylidene]tetrahydrofuran-2-ones

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Abstract
The title photochromic compounds 4 photocyclise to thermally stable blue and infrared active 7-dicyanomethylene-5-oxo-5,7,8,8a-tetrahydro-2-substituted-4,8a-dimethylfuro[33,4-f]benzofurans or benzothiophenes 5 which absorb at longer wavelengths (>100 nm) than the photocyclised compounds 2 from the corresponding photochromic fulgides 1.