prov:value
| - ange, said photochromic compound having the formula: wherein R, is a lower alkyl group, a substituted alkyl group or a phenyl group; R and R are lower alkyl groups, a phenyl group or R and R, combine to form (Cl-l Where n is 4 or 5; X is a hydrogen atom, nitro group, halogen atom, carboxyl group, alkoxy-carbonyl group, lower alkyl group or alkoxy group; and Ym is one or more member of nitro, halog
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