Molecular Engineering of an 2,5-dithiophen-2-yl-pyrrole Bridged Terpyridine-Fe (II) Coordination Polymer toward Multi-State Electrochromic Energy Storage

Abstract

Electrochromic energy-storage materials are of great interest due to their ability to simultaneously achieve reversible color modulation and charge storage, where molecular engineering plays a key role in performance optimization. Herein, a terpyridine-Fe coordinated conjugated polymer (FeSNSTPy) incorporating an 2,5-dithiophen-2-yl-pyrrole (SNS) π-bridge was successfully constructed. The polymer exhibits a dual electrochromic response arising from SNS backbone doping and Fe(II)/Fe(III)-associated MLCT modulation. FeSNSTPy delivers an optical contrast of 34%, fast switching kinetics (tc/tb = 2.4/2.5 s), and a high coloration efficiency of 626.54 cm 2 /C, together with good cycling stability (91% retention after 100 cycles and 77% after 250 cycles). Moreover, the FeSNSTPy film exhibits an areal capacitance of 2.74 mF/cm 2 at 0.1 mA/cm 2 demonstrating its promising electrochemical energy-storage capability. This work provides a feasible strategy for developing multi-state electrochromic coordination polymers toward advanced electrochromic energy-storage applications.