Fluorescence Quenching by Nitro Compounds within a Hydrophobic Deep Eutectic Solvent

Abstract

Hydrophobic deep eutectic solvents (DESs) exhibit immense potential as viable environmentally benign inexpensive alternatives to both nonpolar organic solvents as well as hydrophobic ionic liquids. Pyrene fluorescence and its quenching by five different nitro compounds are used as a tool to examine structural features and solute dynamics within a prototypical hydrophobic DES formed by mixing salt tetra-n-butylammonium chloride (TBAC) as H-bond acceptor with n-decanoic acid (DA) as H-bond donor in 1:2 mol ratio, named TBAC–DA, in the temperature range 298.15–358.15 K. Changes in fluorescence emission intensity, empirical polarity scale, and excited-state intensity decay of pyrene with change in temperature within TBAC–DA are compared and contrasted with those reported within common and popular hydrophilic DESs and water miscible and immiscible ionic liquids. All five nitro compoundsnitromethane, nitrobenzene, 4-nitrobenzaldehyde, 1-chloro-4-nitrobenzene, and 4-nitroanisolequench the fluorescence from pyrene in TBAC–DA; the quenching follows a simplistic Stern–Volmer relation and is purely dynamic in nature. Quenching of pyrene fluorescence by nitromethane is more within TBAC–DA as compared to the hydrophilic DES reline and ionic liquid 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide. It is attributed to the possible stabilization of partial positive charge that develops on the excited pyrene during electron/charge transfer to the quencher by partially/completely dissociated acid groups of the H-bond donor n-decanoic acid. The dynamic quenching constant (K D) and bimolecular quenching rate constant (k q) within TBAC–DA are significantly higher for nitrobenzene in comparison to the other four quenchers. Conformity to the empirical Arrhenius expression is exhibited by the linear behavior of ln k q versus 1/T for all five nitro compounds. While overall pyrene–quencher data does not comply with the Stokes–Einstein relation, each of the pyrene–quencher pair data does. This suggests the dependence of diffusion behavior on the structure of the quencher within TBAC–DA. Pyrene fluorescence is established as an effective tool to characterize such DESs; the DESs can be used as solubilizing media to detect and assess the important class of nitro compounds.

Effect of Water on a Hydrophobic Deep Eutectic Solvent

“…In this work, we focus on a simple prototypical hydrophobic DES consisting of a 1:2 molar ratio of tetrabutyl ammonium chloride (TBAC) and decanoic acid (DecA) (Scheme ) as a model for hydrophobic DESs. This is one of the first reported hydrophobic DESs, and it has been studied for the extraction of organic material from aqueous solutions and for electrochemical and fluorescence applications. ,, We present, to the best of our knowledge, the first comprehensive detailed study of this DES, focusing especially on the effect of a very small water content and its implications for applications, using a wide spectrum of techniques, including molecular dynamics simulations, spectroscopic techniques, especially multinuclear NMR (pulsed field gradient, relaxation times), differential scanning calorimetry (DSC), and by measurements of density, viscosity, and electrical conductivity.…”

Ionic Rigid Organic Dual-State Emission Compound With Rod-Shaped and Conjugated Structure for Sensitive Al3+ Detection

“…Therefore, BSBDS can be used as a convenient and sensitive fluorescent probe for the detection of Al 3+ in drinking water. The dynamic quenching constant (K sv ) is calculated via the Stern–Volmer formula ( Dhingra et al, 2020 ) F 0 /F = 1+K q ×τ 0 ×[Q] = 1+Ksv×[Q], where K q is the dynamic quenching rate constant, τ 0 is the average lifetime of the lumiongens, and [Q] is the concentration of Al 3+ . We got the function of y = 362113.11254x+0.99312, so the quenching constant in Supplementary Figure S5 is 362113 L/mol.…”

“…Therefore, BSBDS can be used as a convenient and sensitive fluorescent probe for the detection of Al 3+ in drinking water. The dynamic quenching constant (K sv ) is calculated via the Stern-Volmer formula (Dhingra et al, 2020)…”

Synthesis, and the optical and electrochemical properties of a series of push–pull dyes based on the 4-(9-ethyl-9H-carbazol-3-yl)-4-phenylbuta-1,3-dienyl donor

“…The lack of photoluminescence of compound N can be attributable to the presence of the nitro groups, well-known to efficiently quench the photoluminescence of luminescent compounds. [109][110] For all dyes, Stokes shift ranging from 50 nm for compound B to 97 nm for compound M could be determined. The largest Stokes shift was obtained for dye M comprising the 2dicyanomethylidene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) group as the acceptor.…”