Origin of Fluorescence from Boranils in the Crystalline Phase

Abstract

A small series of boranil complexes has been studied by fluorescence spectroscopy. Weakly fluorescent in most organic solvents at room temperature, the target compounds display bright emission in the crystalline phase. X-ray diffraction patterns obtained for single crystals indicate a distorted tetrahedral geometry around the O–B–N center with the boron atom being displaced from the plane of the heterobicyclic ring. Consideration of the various bond lengths in comparison with those of reference compounds indicates that the ancillary phenyl ring, bearing different para-substituents, does not make a prominent contribution to the molecular dipole moment in the solid state. Absorption and fluorescence spectra recorded for the crystals remain remarkably similar to those for liquid solutions and display large Stokes shifts. Proximity broadening is observed in one case. The nitrophenyl derivative exhibits additional absorption and emission bands unique to the solid state and could be indicative of an intermolecular charge-transfer transition. The optical properties are discussed in terms of the crystal packing diagrams.

Synthesis, Structure and Photophysical Properties of a New Class of Inherently Chiral Boron(III) Chelates—The tert‐Leucine Complexes

“…1 HNMR (500 MHz, CDCl 3 ) d 8.34 (s, 1H), 7.57-7.48 (m, 2H), 7.39-7.35 (m, 2H), 7.24-7.17 (m, 3H), 7.03-6.97 (m, 2H), 4.04 (d, J = 1.0 Hz, 1H), 1.02 ppm (s, 9H). 11 BNMR (128 MHz, CDCl 3 ) d 6.80 ppm. 13…”

“…These compounds are readily functionalised to provide a wide range of optical band gaps. The main strengths of the BORANIL compounds concern their facile synthesis and their relatively strong emission in the crystalline state [11] . Of course, there are several other classes of fluorescent molecules where a tetrahedral boron(III) centre is used to arrange the ligand into a “rigid” macrocycle [12] .…”

“…The main strengths of the BORANIL compounds concern their facile synthesis and their relatively stronge mission in the crystalline state. [11] Of course,t here are several other classes of fluorescent moleculesw here at etrahedral boron(III) centre is used to arrange the ligand into a "rigid"m acrocycle. [12] In so doing,i tb ecomesp ossible to introduce molecular chirality by appropriate substitution but, in the vast majority of cases, the enantiomersh ave to be isolated by rathert edious separation procedures.…”

External environment sensitive circularly polarized luminescence properties of a chiral boron difluoride complex

“…The emission band around 540 nm in complex 1a is attributed to the para -quinoidal resonance structure in the excited state ( Scheme 2 ). 24 The first emission band in 1a showed a clear bathochromic shift in the solid state ( λ max = 472 nm for crystal and λ max = 463 nm for crystal) compared to that of in solution state ( λ max = 420 nm). The CIE colour coordinates plotted on the CIE1931 chromaticity chart 25 ( Fig.…”

Unusual reaction of (E)-2-[(benzo[d]thiazol-2-ylimino)methyl]-5-(diethylamino)phenol with triphenylborane: crystal structures and optical properties

“…boron complexes using salicylaldimine as a ligand, have emerged as promising materials due to their excellent optical properties, ICT (intermolecular charge transfer), high Stokes shift and simple synthesis (Vidyasagar et al, 2019). An additional advantage of boranils is that their emission characteristics can be adjusted in a flexible way through structural changes such as extending the �-conjugation system, adding donor/acceptor substituents, increasing molecular rigidity and flattening the structures (Frath et al, 2014;Zhao et al, 2019;Mace ´et al, 2021;Al-Sharif et al, 2020). These complexes can be synthesized on a multi-gram scale with a two-step process, including synthesis of a Schiff-base ligand via a condensation reaction between an amine and an hydroxyaldehyde, and complexation with commercial boron compounds (Massue et al, 2021).…”