Donor Fluorescence as a Probe of Energy Transfer*,†

When a system of N similar molecules (the donors) gives its excitation energy rapidly enough to a dissimilar acceptor, the donor fluorescence rate equals the energy removal rate. Analysis of donor fluorescence decay then provides information about the N‐donor system even if the acceptor is chemically unidentified. The dependence of the removal rate on N in a linear polymer in the extreme limit of very strong interdonor coupling is compared with that of very weak interdonor coupling. The principal result is that removal can be slower in the strong coupling limit because standing‐wave excitons tend to avoid boundaries. Possible application of the concept of standing‐wave excitons to photosynthetic units is discussed. The theory of diffusive energy transfer (very weak coupling limit) is also discussed, and some of its basic formulas given in simple form.