Development of Near-Infrared Light-Emitting π-Conjugated Polymers Based on Hypervalent Silicon(IV)-Fused Azobenzene Compounds as a Strong Electron Acceptor

Near-infrared (NIR) light-emitting materials have attracted attention in the fields of optical communication and bioimaging. To improve the utility of NIR light-emitting materials, it is significant to increase their chemical stability and solubility in common solvents. In this study, we synthesize hypervalent silicon(IV)-fused azobenzene (SAz) compounds and their π-conjugated polymers exhibiting NIR emission both in solution and film (maximum photoluminescence (PL) wavelength: λPL = 727–1004 nm, absolute PL quantum yield: ΦPL = 0.3–7.9%). The introduction of a bulky terphenyl group on silicon ensures the sufficient chemical stability of the SAz backbone and solubility of the compounds in common solvents. The SAz compounds have a strong electron-accepting ability reaching −3.87 eV in the lowest unoccupied molecular orbital (LUMO) energy level owing to the combination of the five-coordinated hypervalent silicon and the azobenzene tridentate ligand. By constructing donor–acceptor systems based on π-conjugated polymers, the optical properties are dramatically improved not only by increasing the radiative transition probability but also by suppressing the structural relaxation in the SAz moiety. Our results reveal that hypervalent silicon compounds are promising candidates for the development of advanced NIR light-emitting materials.