Plasmon assisted control of photo-induced excitation energy transfer in a molecular chain

Abstract

The strong and ultrafast laser pulse excitation of a molecular chain in close vicinity to a spherical metal nano-particle (MNP) is studied theoretically. Due to local-field enhancement around the MNP, pronounced excited-state formation has to be expected for the part of the chain which is in proximity to the MNP. Here, the description of this phenomenon will be based on a uniform quantum theory of the MNP–molecule system. It accounts for local-field effects due to direct consideration of the strong excitation energy transfer coupling between the MNP and the various molecules. The molecule–MNP distances are chosen in such a way as to achieve a correct description of the MNP via dipole–plasmon excitations. Short plasmon life-times are incorporated in the framework of a density matrix approach. By extending earlier work the present description allows for multi-exciton formation and multiple dipole–plasmon excitation. The region of less intense and not-too-short optical excitation is identified as being best suited for excitation energy localization in the chain.