Fluorescence Enhancement of Chromophores Close to Metal Nanoparticles. Optimal Setup Revealed by the Polarizable Continuum Model

A direct estimate of changes in the radiative and nonradiative decay rates of a chromophore near metal nanoparticles is obtained using a quantum mechanical description coupled to the polarizable continuum model. The results account for experimentally observed continuous change from decreased to increased fluorescence. The changes are described as the effects of a dependence on the distance and orientation between the chromophore and the metal nanoparticle, as well as the size, shape, number, and type of the metal particles and the influence of the solvent. The chromophore investigated was N,N?-dimethylperylene-3,4,9,10- dicarboximide in combination with silver and gold particles. The study explains and rationalizes how intrinsic characteristics of the metal predetermine the nanoparticle's behavior toward chromophore excitation and decay rates. As a result, the optimal setup (shape, position, orientation) that gives the largest enhancement is revealed