Oliver Kühn

Effective bridge spectral density for long-range biological energy and charge transfer

The role of medium‐induced relaxation of intermediate (bridge) sites in energy and charge transfer processes in molecular aggregates of arbitrary size and geometry is explored by means of Green’s function techniques. The coupling of electronic and (solvent and intramolecular) nuclear degrees of freedom is incorporated using the Brownian oscillator model, which allows an exact calculation of the necessary two‐point and four‐point correlation functions of exciton operators. The signatures of energy transfer and spectral diffusion in time‐ and frequency‐resolved fluorescence spectroscopy are studied. A unified expression for the frequency‐dependent transfer rate is derived, which interpolates between the sequential and superexchange limits. Numerical results and a Liouville space pathway analysis for a donor–acceptor system coupled through a single bridge molecule are presented.

Two‐exciton spectroscopy of photosynthetic antenna complexes: Collective oscillator analysis

The linear and third‐order polarizabilities of the light‐harvesting antennae of photosynthetic bacteria and green plants are calculated using an equation of motion approach which maps the system onto a coupled set of anharmonic excitonic oscillators. The oscillator representation is shown to have several advantages over the traditional picture based on properties of individual global eigenstates of the aggregate; besides a considerable reduction of computational effort, the dynamics of excitations in the two‐exciton band is conveniently analyzed in terms of single‐exciton Green’s functions and the two‐exciton scattering matrix.

Charge and Energy Transfer Dynamics in Molecular Systems: May/Charge

Electronic and Vibrational Molecular States. Dynamics of Isolated and Open Quantum Systems. Vibrational Energy Relaxation and Redistribution. Intramolecular Electronic Transitions. Electron Transfer. Proton Transfer. Exciton Transfer. Concluding Remarks.