INTER-SYSTEM CROSSING CATALYZED BY SOLUTE ENCOUNTERS

We studied the reversible transitions between two levels of excited mo lecule stimulated by encounters with other solutes. The inter-system c rossing results in either quenching or trapping of excitation dependin g on the relationship between the lifetimes of the levels. In the part icular case of an immobile excited molecule and equal lifetimes, an ex act solution of the problem was given which is valid for arbitrary con centration of solutes. We compared the fluorescence quantum yield obta ined with this solution, superposition approximation and integral enco unter theory. Our main conclusion is that for equal lifetimes the latt er has an advantage, even in small concentration limits and is out of competition when the lifetime of the primary excited level is shorter than another. (C) 1998 American Institute of Physics.