Selective modulation of energy levels of frontier orbitals in solid-state luminescent boron-fused azomethine polymers with orthogonal orientations to the main chains

Abstract

The development of polymers with film luminescence and property tuning is still a relevant topic due to concentration quenching which most of the organic luminophores suffer from. Based on boron-fused azomethine (BAm) complexes which can show aggregation-induced emission (AIE) and crystallization-induced emission (CIE), we previously obtained solid-state luminescent polymers. In this study, we synthesized π-conjugated polymers involving BAms orthogonally oriented to the main chains. In particular, the synthesized polymers have quite different properties from parallell-oriented BAm-consisting π-conjugated polymers that have been previously reported. The synthesized polymers can show intense luminescence in solutions and films. Moreover, we found that the energy levels of one of the frontier molecular orbitals (FMOs) can be selectively perturbed depending on the ligand structure. Furthermore, by selecting condensed reagents in the azomethine bond formation reaction, the monomer structure followed by the perturbed FMO can be determined. Finally, we observed that the synthesized polymers exhibit steady emission in both solutions and films in the near-infrared (NIR) region (λ_PL = 686 nm, Φ_PL = 4% in solution, λ_PL = 709 nm, and Φ_PL = 3% in film). Computer calculations support these experimental data. In this study, a new series of solid-state luminescent π-conjugated polymers with tunable energy levels is demonstrated.