A precursor strategy for the synthesis of low band-gap polymers: An efficient route to a series of near-infrared electrochromic polymers

A precursor strategy for the synthesis and screening of a series of conjugated donor-acceptor polymers is demonstrated by successful preparation of low band-gap polymers (P2-P5) containing triphenylamine as an electron donor and several heterocycles as acceptors, such as [1,2,5]thiadiazolo[3,4-g] quinoxaline, [1,2,5]thiadiazolo[3,4-i]dibenzo[a,c]phenazine, benzo[1,2-c:4,5-c′]bis([1,2,5]thiadiazole), and selenadiazole[3,4-f] benzo[c][1,2,5]thiadiazole, that are transformed from a single reactive polymer (P1). Polymers P2-P5 have the band gap of 1.71-1.29 eV and show the absorption and emission in the near infrared (NIR) spectral region. All the polymers are also NIR electrochromic. In particular, polymer P3 is electrochemically switchable between leaf-like green coloring and near-infrared absorbing states with an efficiency of 479 cm² C^-1 at 1310 nm or 232 cm² C^-1 at 1550 nm, making it potentially useful for electrically switchable day-to-night camouflage applications.