# Probing a Reactive Alkyne Center Aligned via a Triphenylmethane Tripod on Au(111) for Electric Field‐Induced Chemistry by STM and TERS

## TL;DR

This study explores how electric fields can control chemical reactions by anchoring a molecule upright on a gold surface and using advanced imaging techniques to confirm its alignment.

## Contribution

A new strategy for aligning a reactive alkyne center upright on a gold surface using a triphenylmethane tripod for electric field-induced chemistry.

## Key findings

- The upright configuration of the alkyne was confirmed using STM and TERS.
- The alkyne remains stable under intense electric fields, enabling in situ monitoring of reactions.
- STM height profiles and Raman intensity data support the alignment of the alkyne along the surface normal.

## Abstract

Electric field‐induced chemistry at the solid/vacuum interface has distinct advantages over enzyme‐ and electrocatalysis because chemical reactivity is solely governed by external electrical fields (EEFs), while other factors such as solvent and ion effects are ruled out. Intense EEFs on the order of 109 V m−1 are generated between the metal tip of a scanning tunneling microscope (STM) and a single‐crystalline metal surface. Reactive centers can be aligned along the direction of the EEF, that is, orthogonal to the metal surface, for experiencing the maximum field. Here, a strategy is introduced to achieve this: a terminal alkyne as a reactive center is connected to the sp3‐hybridized core of a triphenylmethane‐based rigid molecular tripod chemisorbed on Au(111), while its upright configuration is probed experimentally by low‐temperature (LT) ultrahigh‐vacuum (UHV) single‐molecule STM and STM‐based tip‐enhanced Raman scattering (TERS) in conjunction with density functional theory (DFT). The orientation of the alkyne moiety relative to the surface normal is inferred from STM height profiles and particularly the Raman intensity of the dominant C≡C stretching peak. The upright configuration and stability of the alkyne reactive center in the presence of intense EEFs paves the way for future E‐field‐induced chemistry monitored in situ by TERS.

Electric‐field‐induced chemistry at solid/vacuum interfaces offers precise control over chemical reactions. In this study, a triphenylmethane‐based tripod with a terminal alkyne is anchored upright on a gold surface. Advanced scanning tunneling microscopy and tip‐enhanced Raman scattering confirm the alignment and stability of the reactive center, enabling new possibilities for electric‐field‐driven molecular reactions.