DIPOLE-DIPOLE ELECTRONIC-ENERGY TRANSFER - FLUORESCENCE DECAY FUNCTIONS FOR ARBITRARY DISTRIBUTIONS OF DONORS AND ACCEPTORS .2. SYSTEMS WITH SPHERICAL-SYMMETRY

Many interesting systems of nanometer dimensions form spherically symm etric domains, either by design or through spontaneous self-assembly. The technique of direct nonradiative resonance energy transfer (DET) c an be used to characterize the morphology of such structures on a nano meter scale. One needs to label the domain of interest with appropriat e donor and acceptor dye moieties. One measures the fluorescence decay of the donors (I-D(t)) in the presence of accepters. The underlying g eometry and physics of the system dictate how the dyes distribute them selves along the radial axis R of the system, according to concentrati on profiles (C-D(R), and C-A(R)) which need not be uniform. Because DE T is sensitive to the distribution of dye interdistances, I-D(t) conta ins information about the underlying morphology. In this work we obtai n an analytic expression relating I-D(t) to the donor/acceptor concent ration profiles. This extends our previous contribution for systems wi th a plane of symmetry. The expression developed is general and capabl e of handling geometries in both extended and/or restricted spaces. It does not require a specific spatial locus for the donors nor does it require prior calculation of the pair-distribution function of the don or-acceptor distances. The development also provides one with an analy tic expression for the evaluation of the interdistance distribution fu nctions.