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Unique Substitution Effect at 5,5′‐Positions of Fused Azobenzene–Boron Complexes with a N=N π‐Conjugated System
Author(s) -
Gon Masayuki,
Wakabayashi Junko,
Tanaka Kazuo,
Chujo Yoshiki
Publication year - 2019
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201801659
Subject(s) - delocalized electron , conjugated system , substituent , homo/lumo , azobenzene , materials science , photochemistry , band gap , solvatochromism , boron , fluorene , chemistry , polymer , stereochemistry , optoelectronics , organic chemistry , molecule
Abstract A recent report illustrated superior optical properties, such as near‐infrared emission, of polymers connected at the 4,4′‐positions to a fused azobenzene–boron complex (BAz). In this study, it is initially demonstrated that further narrowing of the band gap can be realized through the substituent effect with bromine groups at the 5,5′‐positions of BAz compared with those at the 4,4′‐positions. From a series of mechanistic studies, perturbation of the energy levels was rationally explained by the difference in contributions of the inductive effect and the variable resonance effect, which was correlated with the degree of electron distribution of molecular orbitals at the substituent positions. Moreover, it was found that unique electronic states, such as delocalized HOMOs and LUMOs, 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. By taking advantage of property tunability and the dramatically 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.