Electrochromic conjugated porous polymers based on N,N,N′,N′-tetraphenyl-1,4-phenylenediamine with donor-donor and donor-acceptor structures

Abstract

Conjugated porous polymers (CPPs) have made remarkable progress in the fields of photocatalysts, chemical sensors and optoelectronic devices due to their fully π-conjugated framework and permanent intrinsic porosity, along with high mechanical and photochemical stability. However, electrochromic CPPs have received limited attention to date. Here, a donor–donor (D-D) type CPP bearing N,N,N′,N′-tetraphenyl-1,4-phenylenediamine (TPPA) and 2,2′-bithiophene (BTP) units, and a donor–acceptor (D-A) type CPP bearing TPPA and 4,7-bis(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (TBTh) units were synthesized through the Stille coupling reaction. The D-D polymer P(TPPA-BTP) presents only a p-type doping process and shows a single reversible color change (neutral yellow/oxidized gray), while the D-A polymer P(TPPA-TBTh), which undergoes both p-type and n-type doping processes, demonstrates multicolor switching (reduced green/neutral purple/oxidized gray). In comparison, P(TPPA-BTP) exhibits better kinetic properties in the visible region, while P(TPPA-TBTh) shows superior kinetic properties in the near-infrared (NIR) region. Particularly, P(TPPA-TBTh) displays short response time (0.63 s/1.43 s), high optical contrast (59.2 %), large coloration efficiency (396.6 cm²/C) and desirable kinetic stability (maintaining 88.5 % optical contrast at 1400 nm after 3000 s of electrochromic switching) in the NIR region. This work on the new CPPs might promote further exploration in smart electrochromic materials.