Weber’s Red-Edge Effect that Changed the Paradigm in Photophysics and Photochemistry

Abstract

Weber's red-edge effect is formulated as follows: ``In rigid and highly viscous environments the excited-state energy transfer producing depolarization of fluorescence emission in concentrated dye solutions stops to be observed when fluorescence is excited at the red (long wavelength) edge of absorption spectrum.'' After its discovery, it led to finding of a number of new wavelength-selective effects in spectral shifts, quenching, anisotropy and lifetimes, and also in different excited-state reactions forming a new vision of structural disorder and molecular dynamics in condensed media. These effects were consistently explained based on a new paradigm that accounts for statistical distribution of fluorescence emitters on their interaction energy with the environment leading to static or dynamic inhomogeneous broadening of spectra and to directional excited-state energy homo-transfer. These phenomena can be modulated by the energy of the excitation quanta. Their description, optimal conditions for their observation, information that they carry, and overview of their different applications are the subject of this chapter.