Resonance Energy Transfer

Resonance energy transfer, also known as Förster- or fluorescence- resonance energy transfer, or electronic energy transfer, is a photonic process whose relevance in many major areas of science is reflected both by a wide prevalence of the effect and through numerous technical applications. The process, operating through an optical near-field mechanism, effects a transport of electronic excitation between physically distinct atomic or molecular components, based on transition dipole-dipole coupling. In this chapter a comprehensive survey of the process is presented, beginning with an outline of the history and highlighting the early contributions of Perrin and Förster. A review of the photophysics behind resonance energy transfer follows, and then a discussion of some prominent applications of resonance energy transfer. Particular emphasis is given to analysis and sensing techniques used in molecular biology, ranging from the ‘spectroscopic ruler’ measurements of functional group separation, to fluorescence lifetime microscopy. The chapter ends with a description of the role of energy transfer in photosynthetic light harvesting

Excitation energy transfer between closely spaced multichromophoric systems: Effects of band mixing and intraband relaxation

We theoretically analyze the excitation energy transfer between two closely spaced linear molecular J-aggregates, whose excited states are Frenkel excitons. The aggregate with the higher (lower) exciton band edge energy is considered as the donor (acceptor). The celebrated theory of F\"orster resonance energy transfer (FRET), which relates the transfer rate to the overlap integral of optical spectra, fails in this situation. We point out that in addition to the well-known fact that the point-dipole approximation breaks down (enabling energy transfer between optically forbidden states), also the perturbative treatment of the electronic interactions between donor and acceptor system, which underlies the F\"orster approach, in general loses its validity due to overlap of the exciton bands. We therefore propose a nonperturbative method, in which donor and acceptor bands are mixed and the energy transfer is described in terms of a phonon-assisted energy relaxation process between the two new (renormalized) bands. The validity of the conventional perturbative approach is investigated by comparing to the nonperturbative one; in general this validity improves for lower temperature and larger distances (weaker interactions) between the aggregates. We also demonstrate that the interference between intraband relaxation and energy transfer renders the proper definition of the transfer rate and its evaluation from experiment a complicated issue, which involves the initial excitation condition.Comment: 13 pages, 6 PostScript figure

Single-wavenumber Representation of Nonlinear Energy Spectrum in Elastic-Wave Turbulence of {F}\"oppl-von {K}\'arm\'an Equation: Energy Decomposition Analysis and Energy Budget

A single-wavenumber representation of nonlinear energy spectrum, i.e., stretching energy spectrum is found in elastic-wave turbulence governed by the F\"oppl-von K\'arm\'an (FvK) equation. The representation enables energy decomposition analysis in the wavenumber space, and analytical expressions of detailed energy budget in the nonlinear interactions are obtained for the first time in wave turbulence systems. We numerically solved the FvK equation and observed the following facts. Kinetic and bending energies are comparable with each other at large wavenumbers as the weak turbulence theory suggests. On the other hand, the stretching energy is larger than the bending energy at small wavenumbers, i.e., the nonlinearity is relatively strong. The strong correlation between a mode $a_{\bm{k}}$ and its companion mode $a_{-\bm{k}}$ is observed at the small wavenumbers. Energy transfer shows that the energy is input into the wave field through stretching-energy transfer at the small wavenumbers, and dissipated through the quartic part of kinetic-energy transfer at the large wavenumbers. A total-energy flux consistent with the energy conservation is calculated directly by using the analytical expression of the total-energy transfer, and the forward energy cascade is observed clearly.Comment: 11 pages, 4 figure