Site-selective Red-Edge spectroscopy of disordered materials and microheterogeneous systems: polymers, phospholipid membranes and proteins

For aromatic fluorophores embedded into different rigid and highly viscous media with low structural order the spectroscopic properties do not conform to classical rules. The fluorescence spectra can depend on excitation wavelength, and the excited-state energy transfer, if present, fails at the "red" excitation edge. These Red-Edge effects are observed due to the existence of excited-state distribution of fluorophores on their interaction energy with the environment and the slow (compared with the rate of emission) rate of dielectric relaxations. In these conditions the site-selection can be provided by variation of energy of illuminating light quanta, and the behavior of selected species can be followed as a function of time and other variables. These observations found extensive application in different areas of research: colloid and polymer science, photophysics and molecular biophysics. Site-selection effects were discovered for electron-transfer and proton-transfer reactions if they depend on the dynamics of the environment. In this report we concentrate on fluorescence of 3-hydroxyflavone derivatives as the probes that exhibit the excited-state proton transfer reaction. The studies in polymer films, phospholipid membranes and in complexes with proteins allow characterizing the static and dynamic disorder in these systems.