Unique Substitution Effect at 5,5′ Positions of a Fused Azobenzene-Boron Complex with N=N Double-Bond π-Conjugated System

摘要： The recent report illustrates superior optical properties, such as near infrared emission, from the polymers with the connection positions at 4,4′ positions in the fused azobenzene–boron complex (BAz). In this study, we initially demonstrate that further narrower band gap can be realized by the substituent effect with bromine groups at 5,5′ positions of BAz than that at 4,4′ positions. From the series of mechanistic studies, perturbation of the energy levels were rationally explained by the contribution difference between the inductive effect and the variable resonance effect which is correlated to the degree of electron distribution of molecular orbitals at the substituent positions. Moreover, it was found that unique electronic states, such as delocalized highest occupied molecular orbital and localized lowest unoccupied molecular orbital, should appear on the main chains of the BAz-containing copolymers with fluorene and bithiophene units according to the optical and electrochemical data and theoretical calculations. Taking advantage of property tunability and the dramatic low LUMO energy level (near ?4.0 eV) of the BAz unit, it can be said that BAz should be a conjugated building block favorable for building advanced optoelectronic devices.