Dyadic Green’s function theory of multichromophoric Förster resonance energy transfer near metallic surfaces: Orientation-dependent distance scaling in parallel and perpendicular configurations

Near-field electromagnetic effects play a central role in determining the rate and distance dependence of Förster resonance energy transfer (FRET) in the vicinity of metallic interfaces. In particular, the large density of evanescent modes supported by metal surfaces can substantially modify energy-transfer pathways in multichromophoric aggregates. Building on the generalized FRET framework developed in Poudel, Chen, and Ratner, J. Phys. Chem. Lett. 7, 955 (2016), we formulate a dyadic Green's function theory for multichromophoric FRET (MC-FRET) near metallic surfaces and under nonequilibrium photonic conditions. The resulting framework provides a microscopic description of how donor-acceptor spectral overlap, collective chromophore geometry, and the local electromagnetic environment jointly govern energy-transfer dynamics. Numerical calculations for highly symmetric ring-like chromophore assemblies positioned near an idealized perfect-electric-conductor-like limiting interface show that the transfer rate exhibits strongly tunable and nontrivial distance scaling. Depending on dipole orientation, aggregate configuration, and photonic boundary conditions, the rate follows power-law behaviors of R-8, R-10, R-12, and even R-14, in clear contrast to the conventional single-pair Förster scaling of R-6. These results demonstrate that metallic near fields can fundamentally reshape MC-FRET distance laws and provide a theoretical basis for designing ultrasensitive molecular rulers, directional excitation-energy transport channels, and nanophotonic platforms with programmable near-field mediated transfer characteristics.