Metal-Molecule Electrodynamic Coupling

Centro S3, CNR - Istituto Nanoscienze, v. Campi 213/A, Modena, 41125, Italy stefano.corni unimore.it 

In this chapter, an introduction to the problem of stud5dng the electromagnetically mediated coupling between a molecule and a metal nanoparticle is given. Various models proposed in the literature for this problem are presented, and the most common relations needed to obtain molecular photophysical quantities from the solution of proper electrodynamics problems are discussed. 

Molecular plasmonics involves the interaction between molecules and plasmonics systems such as metal nanoparticles. Such interaction is always mediated by electromagnetic (EM) fields, which determine how the optical properties of the molecules are modified by the presence of the plasmonics system, and vice versa. In this chapter, we shall describe the origin of the coupling and how the relevant quantities can be calculated. In particular regimes 

Edited by Fabio Della Sala and Stefania D Agostino 

The interaction between plasmons and molecular excitations is involved in several different phenomena. The list below is an attempt to enumerate the experimentally observed surface-enhanced properties (as molecular plasmonics phenomena are often termed), and includes bibliographic references to representative works  

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The molecule is a classical oscillating charge density (usually a point dipole) and the metal nanoparticle is a continuous body characterized by the frequency-dependent dielectric function (see Chapter 1). This is by far the most common description of the metal-molecule electrodynamic coupling problem in the literature. Notably, sometimes even the metal nanoparticle is reduced to a polarizable dipole. Depending on the phenomenon under study, this may be acceptable or results in an oversimplification [50]. 

In the classification of models for metal-molecule electrodynamic coupling that we have done in Sec. 5.1, the model that we have described so far (a classical punctiform dipole close to a metal nanoparticle described as a continuous medium) is the simplest. While it has proven to be extremely useful, not only as a mean to grasp the basic physics of molecular plasmonics phenomena, but also to provide semi-quantitative and, sometimes, even quantitative results, it still remains a model empirical in nature. In this section we shall briefly describe models that goes beyond such an approach. 

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