Quantum Mechanical Approach to Solvent Effects on the Optical Properties of Metal Nanoparticles and Their Efficiency As Excitation Energy Transfer Acceptors

We present a tithe-dependent density functional theory (TDDFT) investigation of the solvent effect on the light absorption of metal nanoparticles and on their efficiency as excitation energy transfer (EET) acceptors from organic dyes. The calculations consider both the dye and the metal particle at quantum-mechanical (QM) level, thus including quantum size effects. The results are compared to those of a second method that exploits a continuous dielectric model for the metal nanoparticle while keeping the same QM level for the dye. Both methods use the polarizable continuum model (PCM) for the solvent. The comparison of these two approaches for gold and silver nanoparticles has clarified how their different electronic nature specifically couples with the solvent and leads to different optical properties and EET efficiency. Moreover, a critical comparison of the QM results with the popular Forster approach to EET has been performed, quantifying the inherent limitations of the latter for dye-nanoparticle EET in solution.