Absorption spectra of a supramolecular complex (SC) placed in the proximity of a spherical metal nanoparticle (MNP) are computed. A description of the absorption is used that is based on a density matrix propagation. The applied density matrix theory starts from a microscopic model including the Coulomb interaction between the SC and the MNP. This interaction is dominated by an energy exchange coupling between the excitations of the SC and the multipolar excitations of the MNP. Its nonperturbative consideration results in a shift and a broadening of all Frenkel-exciton levels as well as an oscillator strength change. If a J-aggregate type SC near a MNP is considered, all exciton levels strongly contribute to the absorption what is in contrast to the isolated SC.
The photoinduced switch of the current through a single molecule is studied theoretically by including plasmon excitations of the leads. A molecule weakly linked to two spherical nanoelectrodes is considered resulting in sequential charge transmission scheme. Taking the molecular charging energy (relative to the equilibrium lead chemical potential) to be comparable to the molecular excitation energy, an efficient current switch in a low voltage range becomes possible. A remarkable enhancement of the current is achieved due to simultaneous plasmon excitations in the electrodes. The behavior is explained by an increased molecular absorbance due to oscillator strength transfer from the electrode plasmon excitations and by a net excitation energy motion from the electrodes to the molecule.
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