Trapping Events in Light-Harvesting Assemblies

Abstract

Modern physics tells us that localization of anything at the atomic and molecular scale is unlikely, so let us address the meaning of “excitation derealization.” Consider the process of fluorescence quenching, in which a strongly emitting molecular species F in solution absorbs light and an increasing amount of species Q acts to decrease the fluorescence. When is the original excitation localized? Of course we can say it is “localized” on the entire population F and part of it is “delocalized” or “relocalized” to the population Q. What is generally meant, however, by those who model the system is that after absorption there is a certain probability that the excitation is localized at any given molecule of F, and that as time progresses, any excitation which was originally on a given molecule of F will be found, with a distribution of probabilities, elsewhere. “Elsewhere” could include other molecules of F as well as those of Q. As we will see in Section 2, there also exist more restricted usages of the concepts “delocalized” and “localized.”