Triarylborane π -electron systems with intramolecular charge-transfer transitions

Abstract

Abstract The incorporation of B element into π -conjugated system is an efficient strategy to tune the steric and electronic structure and thus optoelectronic properties of π -electron systems. The vacant p orbital on the tricoordinate B center makes it exhibit several electronic and steric features, such as electron-accepting ability through p- π * conjugation, the high Lewis acidity to coordinate with Lewis bases, as well as the steric bulk arising from the aryl substituent on the B center to get enough kinetic stability. As a result, the boryl group is a very unique electron acceptor. When an electron-donating amino group is present, the triarylboranes would display intense intramolecular charge transfer transitions, which lead to interesting optoelectronic properties and great utilities. This short review summarizes the recent progress in π -electron systems, which contain both B and N elements and thus display intramolecular charge-transfer transitions. The triarylboranes are introduced based on their structural features, including the linear π -system with boryl and amino groups at the terminal positions, the lateral boryl-substituted π -system with amino groups at the terminal positions, the biphenyl π -system with an amino and a boryl groups at o , o ′-positions, nonconjugated U- and V-shaped π -system, macrocylcic π -system with B and N embedded in the ring, B,N-bridged ladder-type π -system, as well as the polycyclic π -system with B embedded in the center.