Thiadiazolo[3,4-c]pyridine as an Acceptor toward Fast-Switching Green Donor-Acceptor-Type Electrochromic Polymer with Low Bandgap

Thiadiazolo[3,4-c]pyridine (PT), an important analog of benzothiadiazole (BT), has most recently been explored as a novel electron acceptor. It exhibits more electron-accepting ability and other unique properties and potential advantages over BT, thus inspiring us to investigate PT-based donoracceptor-type (DA) conjugated polymer in electrochromics. Herein, PT was employed for the rational design of novel donoracceptor-type systems to yield a neutral green electrochromic polymer poly(4,7-di(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-[1,2,5] thiadiazolo[3,4-c]pyridine) (PEPTE). PEPTE revealed a lower bandgap (E-g,E-ele = 0.85 eV, E-g,E-opt = 1.12 eV) than its BT analog and also favorable redox activity and stability. Furthermore, electrochromic kinetic studies demonstrated that PEPTE displayed higher coloration efficiency than BT analog, good optical memory, and very fast switching time (0.3 s at all three wavelengths), indicating that PT would probably be a promising choice for developing novel neutral green electrochromic polymers by matching with various donor units.