Near-infrared-emissive π-conjugated polymers based on five-coordinated silicon formazanate complexes

Abstract

Organic compounds interacting with near-infrared (NIR) light are vital for developing next-generation functional materials. Herein, silicon formazanate complexes and their conjugated polymers with near-infrared luminescence were synthesized using the N₂O₂-type formazanate ligands. In the calculated geometries, the silicon atom possessed square-pyramidal structures. Interestingly, the photophysical properties of the complexes were strongly affected by the types of axial ligands. π-Conjugation efficiently extended through the polymer chains, resulting in narrow energy gaps between frontier orbitals. The emission band from spin-coat films reached the NIR II region (>1000 nm). Theoretical calculations revealed that the square-pyramidal structure at the coordination center should be responsible for the efficient π-conjugation.