On the importance of including intermolecular correlations in the measurement of polymer interdiffusion by fluorescence nonradiative energy transfer

There has been a great deal of recent interest in monitoring polymer interdiffusion with fluorescence nonradiative energy transfer (NRET), a typical experiment consisting of polymer chains labeled with a donor chromophore interdiffusing with chains labeled with an acceptor chromophore, causing an increase in energy transfer efficiency, E. A factor nearly always ignored in models of this process is the fact that chromophore interactions are screened out because of intermolecular correlation effects, leading to a lower E than would otherwise be expected. The model of Dhinojwala and Torkelson (Macromolecules 27, 4817 (1994)) has been modified to include correlations in order to explore the impact that ignoring correlations has on the diffusion coefficients calculated in such experiments. When correlations are included in the model, E is proportional to (Dpt)1/2/x for t