Electric Field-Induced\nSequential Prototropic Tautomerism\nin Enzyme-like Nanopocket Created by Single Molecular Break Junction

Mastering the control of external stimuli-induced chemical\ntransformations\nwith detailed insights into the mechanistic pathway is the key for\ndeveloping efficient synthetic strategies and designing functional\nmolecular systems. Enzymes, the most potent biological catalysts,\nefficiently utilize their built-in electric field to catalyze and\ncontrol complex chemical reactions within the active site. Herein,\nwe have demonstrated the interfacial electric field-induced prototropic\ntautomerization reaction in acylhydrazone entities by creating an\nenzymatic-like nanopocket within the atomically sharp gold electrodes\nusing a mechanically controlled break junction (MCBJ) technique. In\naddition to that, the molecular system used here contains two coupled\nacylhydrazone reaction centers, hence demonstrating a cooperative\nstepwise electric field-induced reaction realized at the single molecular\nlevel. Furthermore, the mechanistic studies revealed a proton relay-assisted\ntautomerization showing the importance of external factors such as\nsolvent in such electric field-driven reactions. Finally, single-molecule\ncharge transport and energetics calculations of different molecular\nspecies at various applied electric fields using a polarizable continuum\nsolvent model confirm and support our experimental findings. Thus,\nthis study demonstrates that mimicking an enzymatic pocket using a\nsingle molecular junction’s interfacial electric field as a\ntrigger for chemical reactions can open new avenues to the field of\nsynthetic chemistry.