Azulene-based conjugated polymers with tuneable near-IR absorption up to 2.5 mu m

A series of near-IR-active conjugated polymers that cover the near-IR spectrum ranging from 1.0 to 2.5 mu m were reported. Polymers based on an alternating p-conjugated donor and acceptor backbone were designed and protonated azulene was chosen as an efficient acceptor due to the excellent stability of the azulenylium ion. The absorption at 2.5 mu m achieved in this study is by far the longest reported for stable near-IR responsive conjugative polymers. The resulting polymers exhibit good solubility and thermal stability, and easy film formation characteristics, which are important for device applications. The near-IR absorption bands were attributed to the intramolecular charge transfer transition, which was confirmed by our DFT calculations. Electrochromic devices constructed using these materials showed stable and high optical contrast, demonstrating the potential application of these polymers in building organic-based near-IR devices.