A Highly Efficient Near-Infrared-Emissive Copolymer with a N=N Double-Bond π-Conjugated System Based on a Fused Azobenzene-Boron Complex.

Fused azobenzene-boron complexes (BAzs) show highly efficient near-infrared (NIR) emission from the nitrogen-nitrogen double bond (N=N) containing π-conjugated copolymer. Optical measurements showed that BAz worked as a strong electron acceptor because of the intrinsic electron deficiency of the N=N double bond and the boron-nitrogen (B-N) coordination which dramatically lowered the energy of the lowest unoccupied molecular orbital (LUMO) of the azobenzene ligand. The simple donor-acceptor (D-A) type copolymer of bithiophene (BT) and BAz exhibited intense photoluminescence (PL) in the NIR region both in the dilute solution (λPL =751 nm, ΦPL =0.25) and in the film (λPL =821 nm, ΦPL =0.038). The BAz monomer showed slight PL in the dilute solution, and aggregation-induced emission (AIE) was detected. We proposed that N=N double bonds should be attractive and functional building blocks for designing π-conjugated materials.