Photoinduced dynamics in a molecule metal nanoparticle complex: Mean–field approximation versus exact treatment of the interaction

Abstract

Photoexcitation of a molecule placed in the proximity of a metal nanoparticle (MNP) is described theoretically. For a sufficient small spatial extension of the whole system the molecule-MNP coupling is given by the instantaneous Coulomb-interaction. The coupling can also be considered in terms of a local field to which an external field has been transferred due to the presence of the MNP. It is known that such an approach can explain a number of observations. However, it fails to describe molecular excited state quenching. By considering the exact molecule-MNP Coulomb-coupling and a related mean field approximation which directly leads to a local field description we investigate this disappearance of excited state quenching in detail. Laser pulse induced dynamics in the molecule-MNP system are studied and the importance of higher multipole excitations in a spherical MNP is underlined. The equivalence of the mean field approximation with the exact approach when calculating spectra of linear absorption is also demonstrated.