Near‐Infrared Photoluminescence and Electrochemiluminescence from a Remarkably Simple Boron Difluoride Formazanate Dye

Abstract

A boron difluoride formazanate dye that exhibits near‐infrared photoluminescence and electrochemiluminescence was produced via a straightforward two‐step synthesis. Examination of its solid‐state structure suggested that the N‐aryl substituents have significant quinoidal character, which narrows the S1–S0 energy gap and leads to the unique optoelectronic properties observed. Cyclic voltammetry studies revealed two oxidation waves and two reduction waves that were electrochemically reversible. Electrochemiluminescence properties were examined in the presence of tri‐n‐propylamine, leading to maximum intensity at 910 nm, at least 85 nm (1132 cm−1) red‐shifted compared to all other organic dyes. This work sets the stage for the development of future generations of dyes for emerging applications, including single‐cell imaging, that require near‐infrared photoluminescence and electrochemiluminescence.

Formazanate coordination compounds: synthesis, reactivity, and applications

“…Donation of a nitrogen lone pair appears to be the origin of the property changes, and evidence of quinoidal character (i.e., bond alternation within the phenyl ring and N-C bonds with significant double bond character) within the N-aryl substituents were observed using X-ray crystallography. 73 The optoelectronic properties of BF 2 complexes of 3-nitroformazanates (61) 64 and triarylformazanates (59) 63,65 are qualitatively similar to those described above. The 3-substituent has a dramatic influence on electrochemical reduction potentials with nitroformazanate complexes reduced more easily than analogous compounds based on 3-cyanoformazantes due to the greater electron-withdrawing character of NO 2 relative to CN.…”

“…77 The origin of this behavior lies in the fact that both the ground and excited states of compound 64 adopt a planar structure as the result of sp 2 hybridization at boron, thus limiting structural reorganization upon photoexcitation and attenuating non-radiative decay. Based on these studies, it is reasonable to assume that 62,64,65,70,73 Compound 78 it may not be surprising that BF 2 formazanates have been shown to be biocompatible during their use as cell-imaging agents (Fig. 8).…”

“…9). 73,75,81 The CV of a solution containing BF 2 formazanate 60d and an excess of TPrA is shown in Fig. 9A.…”

“…(ii) The introduction of an Al ion resulted in N-C aryl bonds with significant p character; a structural feature that appears to have been recently exploited to induce near-IR absorption and emission in similar compounds. 73 (iii) Coordination of Al significantly alters the reactivity at the unsubstituted nitrogen atoms, weakening the N-Bn bonds in trapped species (e.g., 77) and setting the stage for two-electron redox chemistry to be exploited.…”

Optoelectronic Properties of Carbon‐Bound Boron Difluoride Hydrazone Dimers

“…Recently, we reported the photophysical and AIE properties of double‐rotor BODIHYs (e.g., 3 b ) and explored their redox chemistry . The incorporation of a fourth nitrogen atom into the ligand framework of BF 2 formazanates 4 has yielded dyes that found application in fluorescence cell imaging and materials that exhibit near‐infrared emission and electrochemiluminescence …”