Efficient NIR‐Light Emission from Solid‐State Complexes of Boron Difluoride with 2′‐Hydroxychalcone Derivatives

Abstract

This article describes a series of nine complexes of boron difluoride with 2'-hydroxychacone derivatives. These dyes were synthesized very simply and exhibited intense NIR emission in the solid state. Complexation with boron was shown to impart very strong donor-acceptor character into the excited state of these dyes, which further shifted their emission towards the NIR region (up to 855 nm for dye 5 b, which contained the strongly donating triphenylamine group). Strikingly, these optical features were obtained for crystalline solids, which are characterized by high molecular order and tight packing, two features that are conventionally believed to be detrimental to luminescence in organic crystals. Remarkably, the emission of light from the π-stacked molecules did not occur at the expense of the emission quantum yield. Indeed, in the case of pyrene-containing dye 4, for example, a fluorescence quantum yield of about 15 % with a fluorescence emission maximum at 755 nm were obtained in the solid state. Moreover, dye 3 a and acetonaphthone-based compounds 1 b, 2 b, and 3 b showed no evidence of degradation as solutions in CH(2) Cl(2) that contained EtOH. In particular, solutions of brightly fluorescent compound 3 a (brightness: ε×Φ(f) =45,000 M(-1) cm(-1)) could be stored for long periods without any detectable changes in its optical properties. All together, these new dyes possess a set of very interesting properties that make them promising solid-state NIR fluorophores for applications in materials science.

Near-infrared fluorescent probes in cancer imaging and therapy: an emerging field

“…They possessed many interesting properties that were suitable for applications in materials science as unique solid-state NIR fluorophores. 44 Shao et al reported a new class of NIRF dendrimeric quaterrylenediimide dyes exhibiting high photostability and hydrophilicity International Journal of Nanomedicine 2014:9 submit your manuscript | www.dovepress.com…”

Effect of Methoxy Substitution on Supramolecular Arrangement of Borondifluorides of 2'-Hydroxy Chalcones and their Solid-State NIR Fluorescence

“…The data are collected in Table 1. Like the case of 1, [1] the electronic absorption spectra of 2 and 3 in DCM (Figure 1) display an intense lowest-energy transition band located between 450 and 480 nm. The maximum absorption of 3 is at a longer wavelength compared to 1, which may be due to the presence of two electron donor groups on the A ring.…”

“…For the three compounds investigated, we obtained weak values of Φf in DCM (< 2 %) which shows that non radiative deactivation pathways, such as intramolecular rotation processes, are very efficient within those dyes. [1] …”

“…[1] Slow evaporation of solution of 2 and 3 in dry dichloromethane solution containing ethyl acetate afforded single crystals suitable for X-ray structure analysis. Both compounds 1 and 2 are found to crystallize in the monoclinic system with the P21/c space group while 3 adopts the triclinic system with the P-1 space group ( Table 2).…”

“…[1][2][3] Those push-pull systems, in which the BF2-containing cycle acts as A unit, were shown to display emission in the visible part of the spectrum with useful fluorescence emission quantum yields (Φf) in solution [4][5][6][7][8] and intense near infrared (NIR) emission in the solid state. [1][2][3] It is generally admitted that intermolecular interactions in the condensed phase of small organic molecules lead to effective fluorescence quenching. Substitution of π-conjugated systems with bulky side groups that hinder π-π cofacial stacking prevents aggregation-induced quenching, especially in the case of H-aggregation.…”