Evaluation of local polarity of polymer solids by a rigid fluorescent probe of carbazole–terephthalate cyclophane

A novel rigid fluorescent probe, carbazole–terephthalate cyclophane (Cz–TP) was applied to evaluate local dielectric constants (ε) of various polymer solids in a wide range of temperatures. For poly(vinylidene fluoride), the ε increased above the glass transition temperature (Tg), due to relaxations of the polar segment –(CH2CF2)– of the main chain. For poly(alkyl methacrylate)s, the ε increased above the Tg or the melting temperature of the side chain, where motions of the polar ester groups are activated. For cyanoethylated polymers, the ε increased owing to motions of the polar cyano groups at the end of the side chain and the ε corresponded to the dielectric constant evaluated by dielectric relaxation measurement at a high frequency, because the Cz–TP exciplex has a lifetime of tens of nanoseconds. For a cyanoethylated polymer with a high content of cyano groups, the ε was larger at low temperatures than the dielectric constant obtained by the macroscopic dielectric relaxation measurement. These results show that the Cz–TP molecule is a useful probe for evaluation of the local polarity in polymer solids over a wide temperature range and can detect even a small change in ε at transition temperatures such as glass transition, side-chain melting, and side-chain relaxation.