How temperature and hydrostatic pressure impact organic room temperature phosphorescence from H-aggregation of planar triarylboranes and the application in bioimaging

Highly efficient persistent organic room temperature phosphorescence(RTP) has attracted increasing attention because of promising applications in fields of chemical sensors, optoelectronic devices, information security, and bioimaging, etc. Wherein,the crystal engineering of H-aggregation offers stabilization for long-lived triplet exciton for RTP, but the related research is rare because of the scarcity of ideal phosphorescent H-aggregate. Herein, we designed planar tricoordinate organoboron derivatives with molecular arrangement in ideal H-aggregation. The integration of Br atom can largely enhance RTP efficiency through increasing SOC effect, while the antiparallel molecular arrangement causes annihilation of triplet exciton. Thanks to good selfassembly property, their RTP can even be observed in PMMA matrix with doping ratio of merely 1 wt%. We further found that the cryogenic temperature contributes to stabilizing triplet exciton in H-aggregation, leading to red-shifted phosphorescence. By applying high hydrostatic pressure, the phosphorescence was largely enhanced and redshifted, demonstrating the crucial role of H-aggregation on RTP property. In phosphorescent tissue imaging of live mouse, nanoparticles of BrBA exhibited high contrast image via eliminating the interference of autofluorescence.

Triarylborane π-electron systems with intramolecular charge-transfer transitions

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 borylsubstituted 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 polycyclicπ-system with B embedded in the center.