Electrically Driven Nonresonant Single Molecular Switches

Electrical switching of a single-molecule junction provides a practical module to perform sophisticated operations in electronic devices.However,designing an all-electrically-driven molecular switch is a great challenge.Here,we experimentally and theoretically investigated the charge transport characteristics of isoindigo(ISO)-molecules at the single-molecule level using the scanning tunneling microscope break junction technique.We find that the single-molecule junctions of ISO-molecules display bias voltage-driven switching characteristics.These switches are realtime,reversible,and nondestructive under low-bias voltages.Experimental results show that the mechanism of the switch is not the transition from nonresonant charge transport to resonant charge transport,but it is the shift of the frontier orbital energy levels of ISO-molecules and the change of the interfacial electronic coupling with bias voltage.Our results will advance the design of high-performance bias voltage-driven molecular switches.

In Situ Monitoring of Transmetallation in Electric Potential-Promoted Oxidative Coupling in a Single-Molecule Junction

To monitor and investigate chemical reactions in real time and in situ is a long-standing,challenging goal in chemistry.Herein,an electric potential-promoted oxidative coupling reaction of organoboron compounds without the addition of base is reported,and the transmetallation process involved is monitored in real time and in situ with the scanning tunneling microscopy break single-molecule junctions(STMBJ)technique.We found that the electric potential applied determined the transmetallation.At low-bias voltage,the first-step transmetallation process occurred and afforded Au─C-bonded aryl gold intermediates.The electronic properties of organoboron compounds have a strong influence on the transmetallation process,and electron-rich compounds facilitate this transformation.At high-bias voltage,the second-step transmetallation process took place,and the corresponding intermediate(highly reactive diaryl metal complex)was detected with the assistance of Pd(OAc)_(2).Our work demonstrates the applications of STMBJ on in situ monitoring and catalyzing of chemical reactions and provides a new methodology to fabricate singlemolecule devices.

Supramolecular gelator based on a [c2]daisy chain rotaxane:efficient gel-solution transition by ring-sliding motion

A supramolecular gelator based on the bistable [c2]daisy chain rotaxane is designed and synthesized. The reversible actuation of the [c2]daisy chain renders the formed supramolecular gel with acid/base-responsive switching between gel and monomer solution. The efficient switching process is attributed to the ring-sliding effect of the rotaxane in response to acid/base stimuli.The ring-inhibited hydrogen bonding stacking results in a nearly quantitatively disassembly of the gel network after addition of base which is hard to be realized by traditional heating strategy in hydrogen-bonding-supported gel.

Triggering a [2]rotaxane molecular shuttle through hydrogen sulfide

A novel chemically-controlled [2]rotaxane molecular shuttle was successfully designed and synthesized. A H_2 S-responsive bulk barrier was introduced between the two identical recognition stations of the [2]rotaxane to prevent dynamic shuttling of the macrocycle. Upon addition of H_2 S, the complete intramolecular cascade reaction occurs in a controllable manner, resulting in removal of the bulk barrier and the shuttling motion of the macrocycle between the two stations recovers.

An acid-base responsive linear-cyclic polymer rotaxane molecular shuttle with fluorescence signal output

The preparation of intelligent-responsive materials with controllable topology structure has long been a significant objective for chemists in the field of materials science. In this paper, we designed and prepared a linear-cyclic reversible topological structure polymer based on the bistable [1]rotaxane molecular shuttle. A ferrocene-functionalized [1]rotaxane and naphthalimide fluorophore group are introduced into the both ends of the polymer, which exhibit distance-induced photo-electron transfer effect. The structural transformation between linear and cyclic state of polymer is demonstrated by simple acid-base stimuli, accompanying visual fluorescence changes. The transformation process was characterized by 1H NMR spectra and fluorescence spectra. This work provides a novel strategy to construct functionalized polymers with topological structure.