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
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