Novel Pathways for Enhancing Nonlinearity of Organics Utilizing Metal Clusters

We show that ultrasmall metallic nanoparticles can be combined with large second- and third-order response organic chromophores to enhance the overall third-order response of the system. This approach can be used in combination with microscopic cascading to generate exceptionally large third-order response. Intermolecular charge-transfer coupling between the molecules and the metal clusters enhances the real part of the nonlinearity at telecommunication wavelengths, while avoiding plasmonic enhancement of one- and two-photon absorption, and minimizing optical losses. The results of density functional calculations for a molecule with large second-order response, (para)nitroaniline, show that use of a gold cluster as a link between molecular entities enhances third-order nonlinearity. Varying size and shape of the metal cluster as well as the distance between the clusters and the molecules allows fine-tuning of nonlinear response over a large range of magnitudes.