Superior photochromic performance of naphthopyrans in a rigid host matrix using polymer conjugation: Fast, dark, and tunable

The attachment of low T-g poly(n-butyl acrylate) polymers (M-n 4100 to 13 100) to naphthopyran photochromic dyes provided large tunable improvements in their photochromic performance in a rigid thermoset host polymer matrix. Both coloration and decoloration speeds were greatly increased, with the critical t(1/2) decoloration times reduced by 50-95% and t(3/4) decoloration times reduced by at least 63% through the use of these polymer conjugates. In addition, the optical density of the colored form of the dye-polymer conjugates rapidly reached a steady state absorption ca. 60-70% greater than the nonpolymer conjugated control dyes. The effect of the geometry of the polymer conjugates was examined, and it was found that mid-placement of the dye on the polymer provided secondary decoloration speed enhancement over end-placement. Thus, conjugation of low T-g poly(n-butyl acrylate) not only provides faster coloration and decoloration but also greatly increases optical density with near square-wave characteristics.