Evaluation of the distribution of distances between energy donors and acceptors by fluorescence decay.

When transfer of electronic excitation energy occurs between a donor-acceptor pair by the Förster mechanism, the decay of fluorescence of the donor follows first-order kinetics, with a rate constant that depends on the distance from donor to acceptor. In a system that contains donor-acceptor pairs of different separations, the fluorescence decay of the donors will not be exponential, but will depend on the distribution function of donor-acceptor distances, f(r). Various approaches are outlined for the extraction of information about f(r) from the decay curve of donor fluorescence. Specifically, if a plausible expression with adjustable parameters is assumed for f(r), numerical methods can be used to evaluate the parameters that yield the closest fit between the observed decay curve and that calculated from the assumed f(r). The technique of fluorescence decay may prove to be useful for determination of distribution functions of end-to-end distances of polymers to the edges of which suitable donor-acceptor chromophore pairs have been attached.