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

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 fluoresc...