DAMPING AND HIGHER MULTIPOLE EFFECTS IN THE QUANTUM-ELECTRODYNAMIC MODEL FOR ELECTRONIC-ENERGY TRANSFER IN THE CONDENSED-PHASE

The interplay between electronic coupling, spectral linewidth, and rat e of electronic energy transfer between chromophores is examined in th e context of a quantum electrodynamical (QED) model. The QED framework properly allows us to identify the partitioning between the near and far zone mechanisms for transfer of energy between chromophores disper sed in condensed phase (liquid or solid) host media. The extent to whi ch coupling is modified by the medium is investigated. A general QED t reatment of higher multipole contributions to the coupling between tra nsition moments is also derived, whence interactions involving electri c dipole, quadrupole and octopole as well as magnetic dipole and quadr upole interactions are examined explicitly. A new formulation is prese nted wherein expressions for the multipolar coupling tensors are obtai ned in terms of spherical Bessel functions, providing a clear, compact representation of the retarded coupling interaction and its distance- dependence. The irreducible tensor formulation of the coupling is disc ussed, highlighting features concerning the exact form of the orientat ion factors that have often in the past escaped notice. The detailed m ethod of implementing a rotational averaging of the resultant interact ion tensors is demonstrated, finally leading to a novel and concise re presentation for multipolar couplings of arbitrary order. The coupling between bacteriochlorophyll a chromophores is discussed as an example . (C) 1997 American Institute of Physics.