On the interactions between molecules in an off-resonant laser beam: Evaluating the response to energy migration and optically induced pair forces

Abstract

Electronically excited molecules interact with their neighbors differently from their ground-state counterparts. Any migration of the excitation between molecules can modify intermolecular forces, reflecting changes to a local potential energy landscape. It emerges that throughput off-resonant radiation can also produce significant additional effects. The context for the present analysis of the mechanisms is a range of chemical and physical processes that fundamentally depend on intermolecular interactions resulting from second and fourth-order electric-dipole couplings. The most familiar are static dipole-dipole interactions, resonance energy transfer ͑both second-order interactions͒, and dispersion forces ͑fourth order͒. For neighboring molecules subjected to off-resonant light, additional forms of intermolecular interaction arise in the fourth order, including radiation-induced energy transfer and optical binding. Here, in a quantum electrodynamical formulation, these phenomena are cast in a unified description that establishes their inter-relationship and connectivity at a fundamental level. Theory is then developed for systems in which the interplay of these forms of interaction can be readily identified and analyzed in terms of dynamical behavior. The results are potentially significant in Förster measurements of conformational change and in the operation of microelectromechanical and nanoelectromechanical devices.

Interparticle Interactions: Energy Potentials, Energy Transfer, and Nanoscale Mechanical Motion in Response to Optical Radiation

“…Another such combination, which we have pointed to but not fully discussed in the previous text, conflates optical binding and RET. In this prospect, further mechanical motion may arise as the potential energy of optical binding may differ if either (or both) interacting particle is excited via RET or direct absorption . This contrasts with conventional optical binding, where both particles are normally in their ground state.…”

A retarded coupling approach to intermolecular interactions

“…(iv) The retarded potential tensor is given by the usual expression (5), V {k j }{k j +1 } (κ, R ξ j +1 ξ j ), where its parametric dependence is on the effective wave-vector magnitude κ as given by (15), while R ξ j +1 ξ j is the separation of the two centres linked by the retarded potential.…”

“…In connection with optical binding, for example, the interactions of neighbouring static electric and induced dipoles produce the potential energy landscapes that determine local forces and positions of equilibrium [8,9], while the dynamic interactions between transition dipoles are responsible for intermolecular energy transfer [10][11][12]-the latter itself a process that engenders modifications to the local force fields [13][14][15]. When off-resonant radiation propagates through a molecular system it engages further pair interactions that are reflected in optical binding forces [16,17] and modifications to the rates of energy transfer [18].…”

Controlling resonance energy transfer in nanostructure emitters by positioning near a mirror

“…Their lifetime is limited by the time-energy uncertainty principle manifesting in one or more emission-absorption processes. [18][19][20] Generally, RET is the dominant energy transfer mechanism between emitters (a donor and an acceptor) in nanometer proximity, where, typical of the Förster theory, the rate has a 6 distance dependence (R here is the separaquestions regarding the underlying mechanism leading to this remarkably high efficiency.…”