Electric-field control of single-molecule tautomerization

Abstract

The electric field is an important parameter to vary in a single-molecule experiment, because it can directly affect the charge distribution around the molecule. Yet, performing such an experiment with a well-defined electric field for a model chemical reaction at an interface has proven to be extremely difficult. Here, by combining a graphene field-effect transistor and a gate-tunable scanning tunneling microscope (STM), we reveal how this strategy enables the intramolecular H atom transfer of a metalfree macrocycle to be controlled with an external field. Experiments and theory both elucidate how the energetic barrier to tautomerization decreases with increasing electric field. The consistency between the two results demonstrates the potential in using electric fields to engineer molecular switching mechanisms that are ubiquitous in nanoscale electronic devices.

Tailoring Tautomerization of Single Phthalocyanine Molecules through Modification of Chromophore Photophysics by the Purcell Effect of an Optical Microcavity

“…Because of these intriguing properties, tautomerization reactions have been proposed to act as molecular switches. Thus, finding a “‘physical”’ method of manipulating tautomerization, and other intramolecular reactions, is crucial to design and control molecular optoelectronics. , Here, we have investigated the influence of the Purcell effect on the tautomerization of single molecules at room temperature by placing single PcS 4 molecules inside an optical λ/2 microcavity. Molecules on resonance with the microcavity mode have a shorter fluorescence lifetime, and the excited singlet state is depopulated faster; as a consequence, the transition rate to the triplet state is reduced.…”

“…Probing − and controlling − tautomerization has attracted significant research attention due to its fundamental importance in many biological and chemical processes . Within porphyrin , and phthalocyanine , derivatives, NH tautomerization occurs when the two inner hydrogen atoms migrate in the framework of the cavity consisting of four nitrogen atoms.…”

“…Liljeroth et al demonstrated that a voltage pulse at the STM tip could induce switching of tautomerization in single naphthalocyanine molecules adsorbed on ultrathin insulating films at low temperature. Most recently, Mangel et al have also controlled the intramolecular proton-transfer reaction in phthalocyanine molecules by lowering the tautomerization barrier with a static electric field. However, an optical microcavity allows to influence the photophysical properties without modifying the local environment or the molecular structure but altering the excited state lifetime due to the Purcell effect, an alteration of the spontaneous emission rate by modifying the local density of optical states (LDOSs) .…”

Twistable dipolar aryl rings as electric field actuated conformational molecular switches

“…Large and reversible jumps of conductance triggered by E-fields can be achieved by means of changes in the redox state of electrochemically active molecules 5,6,7 , molecular conformational rearrangements 8,9,10,11,12,13 , and structural changes in the electrode-molecule contacts. 14,15 Electrically controlled switching is also possible through E-field-induced molecular tautomerizations, isomerizations, conformational changes or rotations in molecular crystals 16 , in solution 17 , in frozen molecular solids 18 , in molecules adsorbed on surfaces 19,20,21,22,23,24 and in encapsulated molecules. 25 It is noted that external E-fields can even catalyze bond rupture processes 26 or more complex reactions at the single-molecule level 27,28,29 .…”

Multidimensional Hydrogen Tunneling in Supported Molecular Switches: The Role of Surface Interactions

“…Tetrapyrrole macrocycles, like porphyrin, naphtalocianine, and porphycene, show a remarkable diversity of functional properties [11][12][13][14][15], and were proposed, among others, as molecular switches [16][17][18]. The intramolecular hydrogen transfer reaction that occurs in the inner cage of these molecules, known as tautomerization, can be triggered remotely by different external stimuli [19][20][21][22][23][24]. Moreover, because the reaction takes place without a pronounced conformational change, these molecules can be incorporated in nanoscale devices.…”