prov:value
| - Of particular interest, are photochromic materials represented by graphic formulae VIIIA and VIIIB wherein Y is N; R1 is a C1 -C4 alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, secondary butyl, isobutyl and tertiary butyl; R2 and R3 are each methyl, ethyl or phenyl; R12 is selected from C1 -C4 alkyl, C1 -C4 alkoxy, chloro, fluoro or cyano; R10 is selected from hydrogen, fluoro, triflu
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