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

Abstract

Chemical reactions such as bond dissociation and formation assisted by localized surface plasmons (LSPs) of noble metal nanostructures hold promise in solar-to-chemical energy conversion. However, the precise control of localized plasmons to activate a specific moiety of a molecule, in the presence of multiple chemically equivalent parts within a single molecule, is scarce due to the relatively large lateral distribution of the plasmonic field. Herein, we report the plasmon-assisted dissociation of a specific molecular site (C–Si bond) within a polyfunctional molecule adsorbed on a Cu(100) surface in the scanning tunneling microscope (STM) junction. The molecular site to be activated can be selected by carefully positioning the tip and bringing the tip extremely close to the molecule (atomistic approach), thereby achieving plasmonic nanoconfinement at the tip apex. Furthermore, multiple reactive sites are activated in a sequential manner at the sub-molecular scale, and different sets of products are created and visualized by STM topography and density functional theory (DFT) modeling. The illustration of site-selective activation achieved by localized surface plasmons implies the realization of molecular-scale resolution for bond-selected plasmon-induced chemistry.

Scanning probe microscopy in probing low-dimensional carbon-based nanostructures and nanomaterials

“…In addition, on-surface synthesis of carbon-based nanostructures and nanomaterials strongly relies on either thermal excitation or atom manipulation (by means of injecting tunneling electrons) so far, while other extensive excitation sources (such as photo-excitation [169][170][171][172][173] and localized surface plasmons [174][175][176][177] as illustrated in the bottom panel of figure 9) have been much less reported or applied in synthesis. Given that thermal excitation would activate several chemical groups simultaneously, poor reaction selectivity has long been a realistic obstacle.…”

“…Besides, for pericyclic reactions, selection rules (also known as Woodward Hoffmann rules) indicate that some reactions would be ground state (thermally) allowed, while others would be excited state (photochemically) allowed yet thermally forbidden. Notably, plasmoninduced reactions by confining light at the SPM junction can significantly reduce the energy requirements and facilitate efficient energy conversion with a strong enhancement of the electric field [174,176,177]. Thus, integration of a broader range Moreover, intact deposition of carbon-based molecular precursors or structures is not only prerequisite for on-surface synthesis protocol, but also essential for direct investigation under UHV conditions (cf upper right panel of figure 9).…”

Tip-Enhanced Raman Imaging of Photocatalytic Processes at the Nanoscale

“…Ultrahigh vacuum (UHV) TERS offers (i) direct visualization of molecular analytes with angstrom spatial resolution and (ii) precise control of the molecular environment. ,,, Using the advantage of UHV-TERS, the Hou and Jiang groups were able to probe weak molecule–substrate interactions and conformations of molecular analytes on the metal surfaces. ,− Furthermore, Xu and co-workers demonstrated that an electric field of the scanning probe can be used to trigger conformational changes in pentacene adsorbed on Ag(110) . Specifically, the researchers observed α to γ conformational changes in the central benzene ring of pentacene.…”

“…Using TERS, the researchers demonstrated that α to γ conformational changes were caused by C–H bond breaking at the central benzene ring of pentacene followed by the skeleton deformation of this molecule. Recently, the Jiang group reported that a scanning probe could be used to trigger a dissociation of specific molecular site (C–Si bond) in individual 5,10,15,20-tetrakis­[(trimethylsilyl)­ethynyl]­porphyrin molecules adsorbed on a Cu(100) surface, Figure . To enable such bond scissoring, the scanning probe had to be positioned precisely at the chemical bond atop the molecule.…”

“…STM image, ball-and-stick model, and calculated adsorption geometry (top view) for 4L (a, b, c), 3L (d, e, f), 2L (g, h, i), and 1L (j, k, l), respectively. Reprinted with permission from ref . Copyright 2022 American Chemical Society.…”