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.