Site-selective Red-Edge effects.

Observation of Red Edge effects is the basis of unique methodology that allows combination of site-photoselection with dynamics of molecular relaxations. The important dynamic information on molecular level can be obtained even by simple recording of steady-state fluorescence using the lifetime as the time marker. The extension to time domain allows distinguishing these relaxations from other dynamic processes that influence the excited-state energies. In this Chapter I briefly discuss the background of this technique and concentrate on quantitative measure of these effects and on importance of their distinction from ground-state heterogeneity. The peculiarity of Trp emission in proteins and the optimal selection of fluorescence probes are discussed. The Red Edge excitations influence dramatically the excited-state reactions that are coupled with dielectric relaxations and this opens a new fascinating prospect for protein and biomembrane studies.