Distance and Orientation Dependence of Excitation Energy Transfer: From Molecular Systems to Metal Nanoparticles

The elegant theory developed by Forster to describe the rate of fluorescence resonance energy transfer between a donor and an acceptor has played a key role in understanding the structure and dynamics of polymers, biopolymers (proteins, nucleic acids), and self-assemblies (photosystems, micellar systems). Forster theory assumes the transition charge densities of donor and acceptor molecules are point dipoles and hence predicts a 1/R6 dependence of energy transfer rate on center-to-center separation distance, R. In addition, a preaveraging over the orientations of the two dipoles is usually performed. The present review examines the validity of these assumptions in following different donor−acceptor (D−A) systems: (i) dye molecules attached to a flexible polymer chain in solution, (ii) extended conjugated dye molecules in quenched conformation, (iii) dye and a spherical metal nanoparticle of different sizes, (iv) two spherical metal nanoparticles, and (v) two prolate shaped metal nanoparticles at different...