Design Rules for Improving the Cycling Stability of High-Performance Donor-Acceptor-Type Electrochromic Polymers.

Although high-performance donor-acceptor (D-A)-type polymers have received much attention as an important class of electrochromic materials, the related studies have mostly focused on the influence of D and A units on the band gap, onset potential, and switching time, leaving the effect of D-A structures on cycling lifetime underexplored. Herein, we design and synthesize a series of poly(aryl amino sulfone)s (PAASs) as D-A polymers with TPA-based donor units and the sulfone moiety as the acceptor unit. As a result, we present new rules to design and develop D-A structure polymers with high EC cycling stability: (1) the electron donating and withdrawing abilities of donor and acceptor should be balanced during the electrochemical cycle process, and this balance can be measured by the ratio of Jred/Jox; (2) the donor-acceptor structure should benefit to generate lower Eonset. By these design rules, the best-performing polymer PAAS-TPPA-OMe exhibits excellent long-term cycling stability (over 3,900 cycles), low onset potential (0.26 V), fast switching time (6.0/4.3 s for the electrochromic process), high contrast (87% at 688 nm and 94% at 928 nm), and high coloration efficiency (500 cm2 C-1 at 688 nm and 1131 cm2 C-1 at 928 nm).