The polarity sensitivity factor of some fluorescent probe molecules used for studying supramolecular systems and other heterogeneous environments

Abstract

Fluorescence spectroscopy provides an excellent technique for investigating heterogeneous systems, due to its high sensitivity and the large effect of the local environment on molecular emission. In addition, the use of polarity-sensitive fluorescent probes as guests in supramolecular host–guest inclusion complexes can be exploited in fluorescent sensors. This paper identifies, tabulates, and quantifies a series of useful polarity-sensitive fluorescent probes, with a wide range of polarity-dependent fluorescence responses. The degree of polarity sensitivity is quantified using the polarity sensitivity factor (PSF), developed in our laboratory. In most cases, such polarity-sensitive probes show increased emission as the local polarity is decreased (PSF > 1); 10 such probes are described. However, less commonly, “reverse polarity dependence” can occur in which probe emission decreases with decreasing polarity (PSF < 1); four such probes are described. The mechanism for the observed polarity-induced fluorescence changes will also be discussed in selected representative cases. The purpose of this paper is to present details on a broad arsenal of polarity-sensitive fluorescence probes with varying properties, with potentially useful applications in the study of heterogeneous systems, including inclusion phenomena, and in practical applications such as fluorescent sensors, which will be useful to researchers studying supramolecular and other heterogeneous systems using fluorescence spectroscopy.

A Reconfigurable, Dual-Output INHIBIT and IMPLICATION Molecular Logic Gate

“…Nevertheless, the nonradiative quenching constant k nr reduces from 7.58 × 10 8 s −1 in CH 3 CN to 0.46 × 10 8 s −1 in C 7 H 8 (Baruah et al, 2006). In agreement with these data, as well as other examples of polarity-sensitive dyes for which emission is substantially increased with a decrease in solvent polarity (Wagner et al, 2018), the emission spectrum of compound 1 dissolved in toluene (1 in Figure 3) displays a strong fluorescence band. Noticeably, the emission maximum shifts hypsochromically from 710 nm in CH 3 CN (polar solvent) to 640 nm in C 7 H 8 (non-polar solvent) and is accompanied by a gain of fine structure and a decrease in bandwidth.…”

“…Such behavior mirrors what is observed for the molecular switch 1 dissolved in a polar solvent (CH 3 CN), which is known to accelerate internal conversion and consequently quenches the fluorescence of the unprotonated species. It is possible that residual hydroxyl groups remaining on the glass surface after treatment with piranha solution are responsible for the relatively high polarity of the local environment, which commonly decreases the emission intensity, and hypsochromically shifts the absorption (compare Figures S1, S2, S4; Wagner et al, 2018). The utilization of a polar protic solvent (EtOH) for the immersion solutions would also have maintained a polar environment during the switching cycles.…”

Elucidating the Role of Optical Activity of Polymers in Protein–Polymer Interactions

“…8-anilino-1-naphthalenesulfonic acid (ANS) is an extrinsic fluorescence dye that exhibits a blue-shifted emission spectrum and significantly increased emission intensity when binding to hydrophobic sites. For example, the intensity of its fluorescence is nearly 200 times larger in ethanol than in an aqueous solution [ 32 ]. This large sensitivity of ANS fluorescence to the polarity and nature of its microenvironment is a result of a combination of factors, including the effect of polarity on its excited-ground state energy gap and specific solvent–solute interactions [ 33 ].…”

Incorporation of Manganese Complexes within Hybrid Resol-Silica and Carbon-Silica Nanoparticles

“…However, this is not the case for the 9-anthracene carboxylic acid, which displays sensitivity to the polarity of its environment [ 12 , 13 , 14 ]. Modification of the luminescence properties of the 9-anthracene carboxylic acid has been widely discussed, and multiple explanations are proposed: acid-base equilibrium, solvent or concentration-dependent formation of dimers or higher order aggregates, and structural reorganisation of the anthracene ring occurring in excited states [ 11 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Thus, the modification of the 9-anthracene carboxylate ligand luminescence can provide information on its coordination, concentration, and the pH of its environment.…”