Comprehensive Modulation of Naphthopyran Photochromism in a Rigid Host Matrix by Applying Polymer Conjugation

Naphthopyran polymer conjugates of various rigidities were synthesized by atom transfer radical polymerization (ATRP), and their photochromic properties were tested within a rigid host matrix. Broad tuning of photochromic kinetics was displayed as a result of polymer conjugation because of its ability to alter the local environment of the naphthopyran within the host. End-functionalized conjugates, synthesized from a naphthopyran-functionalized ATRP initiator, allowed systematic tuning of kinetics via modulation of chain length of attached polymer. Reducing the rigidity of the conjugate resulted in an acceleration of kinetics and an increase in colorability. Pronounced chain lengths of poly(methyl methacrylate) (> 18 000 g/mol) were required for decoloration kinetics to be effectively depressed compared with an unconjugated naphthopyran control. Random in-chain incorporation of the naphthopyran was afforded by copolymers made with naphthopyran-functionalized monomers. At the expense of a defined placement of the dye moiety with respect to the conjugated polymer chain, such conjugates displayed a pronounced ability to influence the kinetics. Persistent color due to thermally stable isomer populations was observed for all samples and found to be uninfluenced by polymer conjugation.