Anisotropic excitation transfer to acceptors randomly distributed on surfaces.

We presented exact expressions for the ensemble averaged decay of the excitation of a donor molecule due to the energy transfer via anisotropic dipolar interactions to acceptors distributed randomly on a surface. The disorder extended both over the positions of the acceptors and over the orientations of their transition dipoles with respect to that of the donor molecule. Several cases were considered explicitly (a) random orientations of the acceptors in space, with the donor being (a1) perpendicular to the plane, (a2) in the plane, (a3) randomly oriented in space; (b) random orientations of both donor and acceptors in the plane; (c) parallel orientations of donor and acceptors (no orientational disorder). For all these cases we evaluated the analytic, Förster-like expressions, valid for long times and low acceptor densities, and obtained their domains of validity by comparison with the exact, numerically calculated decay laws.