Plasmon Hybridization Model in Molecules: Molecular Jackhammers

We recently demonstrated molecular plasmons in cyanine dyes for the conversion of photon energy into mechanical energy through a whole-molecule coherent vibronic-driven-action. Here we present a model, a molecular plasmon analogue of molecular orbital theory and of plasmon hybridization in metal nanostructures. This model describes that molecular plasmons can be obtained from the combination or hybridization of elementary molecular fragments, resulting in molecules with hybridized plasmon resonances in the electromagnetic spectrum. We applied our approach to the hybridization of the benzoindole and heptamethine fragments for understanding of the resonance frequencies in cyanines using UV-vis and Raman spectroscopy. The molecular plasmon resonances in cyanines are tunable by engineering molecular structure modifications and controlling the dielectric constant of the medium in which the cyanines are dissolved. We measured the plasmonicty index, an easy-to-use and powerful tool to predict and quantify if an organic molecule in solution is a molecular plasmon. This is done by analyzing the UV-vis spectrum as a function of the change of the dielectric constant of the solvent. Our model provides a tool for understanding how to manipulate chemical structures and their interaction with light at the molecular scale as plasmon-driven molecular machines for applications at the interface with biological structures.