Backbone engineering of N,N,N′,N′-tetraphenyl-1,4-phenylenediamine-based conjugated porous polymers toward enhanced electrochromic behavior

Abstract

Tailoring the properties of functional polymers through simple structural modifications is a fascinating molecular design strategy. In this work, cyano functionalization of the polymer backbone improved the electrochromic properties of the conjugated porous polymer (CPP) composed of N,N,N′,N′-tetraphenyl-1,4-phenylenediamine (TPPA) and thienylene-vinylene-thienylene (TVT) units. The non-cyanated polymer P(TPPA-TVT) shows multicolor behavior, reversibly switching among orange-yellow, gray-green, and gray. The cyanated polymer P(TPPA-TVTCN) not only exhibits a different neutral-state color but also presents more diverse electrochromic color changes, including brick red, reddish brown, brown, green, and gray-cyan. In addition, the modification of the cyano group improves the cycling stability of the polymer. P(TPPA-TVTCN) retains over 96% of its initial optical contrast after 2000 seconds of repeated redox switching, with a performance significantly superior to that of P(TPPA-TVT). Moreover, P(TPPA-TVTCN) shows better kinetic properties than P(TPPA-TVT) in the near-infrared (NIR) region. At 1380 nm, P(TPPA-TVTCN) displays an optical contrast of 52.6%, response times of 0.76 s and 2.05 s, as well as a coloration efficiency of 231.52 cm² C⁻¹. The incorporation of the cyano group promotes the formation of a D–A configuration and hence optimizes the optoelectronic properties of the polymer. Besides, the porous structures and extended π-conjugated backbones of the two CPPs help reduce the response time and enhance the cycling stability. Rational polymer design and facile structural adjustment provide an effective way for developing new electrochromic materials.