Plasmon-Driven Motion of an Individual Molecule

Abstract

We demonstrate that nanocavity plasmons generated a few nanometers away from a molecule can induce molecular motion. For this, we study the well-known rapid shuttling motion of zinc phthalocyanine molecules adsorbed on ultrathin NaCl films by combining scanning tunneling microscopy (STM) and spectroscopy (STS) with STM-induced light emission. Comparing spatially resolved single-molecule luminescence spectra from molecules anchored to a step edge with isolated molecules adsorbed on the free surface, we found that the azimuthal modulation of the Lamb shift is diminished in case of the latter. This is evidence that the rapid shuttling motion is remotely induced by plasmon-exciton coupling. Plasmoninduced molecular motion may open an interesting playground to bridge the nanoscopic and mesoscopic worlds by combining molecular machines with nanoplasmonics to control directed motion of single molecules without the need for local probes.

Evidence of exciton-libron coupling in chirally adsorbed single molecules

“…This appearance is the result of averaging over two geometrically equivalent metastable chiral adsorption configurations, between which the molecule rapidly switches upon injection of electrons 12 , 13 , 16 , 29 , 30 . The motion between these two configurations (called switching 16 , 29 or shuttling 12 , 17 ) is represented by the larger grey arrow in Fig. 1a .…”

Mapping Lamb, Stark, and Purcell Effects at a Chromophore-Picocavity Junction with Hyper-Resolved Fluorescence Microscopy

“…Therefore, this signal solely reflects the optical characteristics of the chromophore and can be used to generate subnanometric fluorescence maps of the molecular transition charge density, as we detail below. On the other hand, the energy of the chromophore fluorescence line depends on a subtle interplay between photonic Lamb [28,38,46] and Stark shifts [47,48] induced by the presence of the tip. Whereas the former provides intimate details of the exciton-plasmon coupling, the latter reveals information about the transfer of charges associated with the chromophore electronic transition.…”

Controlling Localized Plasmons via an Atomistic Approach: Attainment of Site-Selective Activation inside a Single Molecule

“…Although chemical reactions assisted by LSPs have been extensively demonstrated in the past decade, the control of a localized plasmonic field toward the formation of desired products remains extremely difficult and thus challenging to attain. In order to address this, nanoscale investigations are required, which lead to the integration of the scanning tunneling microscope (STM) with optical excitation by light , and luminescence from the STM tip–sample junction. − Recently, by combining light with the STM, i.e., through the illumination of the nanogap between the plasmonically active STM tip and the metal substrate by visible light, the plasmons can be excited, and a confined, intense localized electromagnetic (EM) field can be generated at the tip apex, which can provide details to locally understand plasmon-induced changes. − In recent years, STM combined with optical excitation has been successfully employed for local chemical reactions assisted by LSPs. , With such an approach, a certain type of chemical bond within small organic molecules such as dimethyl sulfide (S–S bond) and oxygen (O–O bond) , has been activated by localized plasmons. Maintaining the typical tip–sample distance at ∼1 nm or more, the plasmonic confinement at the tip apex (that dictates the lateral distribution of the plasmonic field, typically on the order of ≈5–10 nm) , remains a critical aspect in single-molecule plasmon-induced chemistry, as it could affect other molecules beyond the molecule directly underneath the tip.…”