The Determination of the Förster Distance (R 0) for Phenanthrene and Anthracene Derivatives in Poly(methyl methacrylate) Films

Experiments that employ direct resonance energy transfer (DET) to obtain information about distances or domain sizes in polymer systems require independent information about the magnitude of the characteristic (Förster) energy transfer distance R 0. Values of R 0 are relatively straightforward to obtain by the traditional spectral overlap method (R 0 SO) for dyes in fluid solution, but are much more difficult to obtain for dyes in rigid polymer films. Here one can obtain a value for R 0 as a fitting parameter (R 0 FF) for donor fluorescence decay experiments for samples containing a random distribution of donor and acceptor dyes in the polymer film. In previous experiments from our group, we needed values of R 0 for various phenanthrene (Phe, donor) and anthracene (An, acceptor) derivatives. In this paper, we describe experiments which determine R 0 values by both methods for a series of Phe-An donor−acceptor pairs in poly(methyl methacrylate) and polystyrene films. Both the location of substituents on the donor and acceptor as well as the choice of the medium had an effect on the measured R 0, which varied between 2.0 and 2.6 nm. We also ascertained that there is some unknown factor, also prevalent in the work of others, which results in the Förster radius being larger when determined by the Förster fit method than by the method of spectral overlap.