prov:value
| - The photochromic article of claim 20 wherein R1 is a methyl, methoxy, formyl, benzo, methoxycarbonyl, or methylaminocarbonyl; R2 is hydrogen; R3, R4 and R5 are each methyl, methoxy, or fluoro; R6 is methyl, methoxy, formyl, methoxycarbonyl, or methylaminocarbonyl; and a, b and d are each the integers 0 or 1, and c is the integer 0, 1, or 2.
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