Neutrally colourless, transparent and thermally stable polynorbornenes viaring-opening metathesis polymerisation for near-infrared electroactive applications

Abstract

Two novel near-infrared (NIR) electrochromic polynorbornenes, poly(NBDTPA) and poly(HNBDTPA), containing electroactive chromophores, were prepared via ring-opening metathesis polymerisation from a new norbornene derivative (NBDTPA) using Grubbs' catalysts followed by hydrogen reduction. The glass transition temperatures (T_g) of poly(NBDTPA) and hydrogenated poly(HNBDTPA) were 141 °C and 91 °C, respectively. The 10% weight-loss temperatures of hydrogenated poly(HNBDTPA) and poly(NBDTPA) were up to 440 °C and 397 °C, respectively. Hydrogenated poly(HNBDTPA) film showed excellent transparency (up to 91%). Poly(NBDTPA) showed a cyclic voltammogram and electrochromic behaviour that was similar to poly(HNBDTPA). The cyclic voltammogram of a poly(HNBDTPA) film cast onto an indium-tin oxide (ITO)-coated glass substrate exhibited three reversible oxidation redox couples at 0.63, 0.82 and 1.23 V vs. Ag/Ag⁺ in acetonitrile solution. The electrochromic characteristics of poly(HNBDTPA) showed excellent stability and reversibility, with multi-stage colour changes from its colourless neutral form to green, light-blue and dark-blue with applied potentials of 0 to 1.75 V. The colour switching time and bleaching time of the poly(HNBDTPA) were 7.1 s and 4.2 s in the near-infrared region (1230 nm), and 7.4 s and 4.5 s in the UV-vis region (420 nm), respectively.