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.