Multiparametric fluorescence probing of nanoscale compositions and biological systems

We demonstrate a possibility for simultaneous probing of several microscopic physicochemical properties of supramolecular systems using the dye molecules existing in several forms of the ground and/or excited states. This idea is realized on a series of 3-hydroxychromone dyes, which exhibit the Excited-State Intramolecular Proton Transfer reaction resulting in two excited state tautomeric forms. Microenvironment of these dyes can be characterized by a number of characteristic energies of absorption and emission transitions (positions of the corresponding bands) and by redistribution between the forms (relative intensities of the bands). We demonstrate that the positions and relative intensities of fluorescence excitation and emission bands can serve as independent variables with different sensitivity to polarity, electronic polarizability, electric field effects, hydrogen bonding acidity and basicity, thus, allowing multiparametric description of probe environment. The results of numerous applications of this approach in the studies of neat solvents, solvent mixtures, proteins and phospholipid membranes are presented.