Photoconductance Induced by Excited-State Intramolecular Proton Transfer (ESIPT) in Single-Molecule Junctions.

Excited-state intramolecular Proton Transfer (ESIPT) molecules have been drawing considerable attention due to their unique photophysical properties and potential applications in optoelectronic devices. Although ground and excited-state tautomerism in various proton transfer systems associated with ESIPT has been extensively studied both experimentally and theoretically, the charge-transport characteristics of ESIPT molecules at the single-molecule level has been little investigated. In this work, scanning tunneling microscope-based fixed junction technique (STM-FJ) is employed with theoretical calculations to explore the electronic properties of SMe-PhOH (with ESIPT properties), together with its photoconductance induced by ESIPT photocycle processes under continuous light illumination (254/275/295/310 nm).

Effect of S⋯π interactions on the charge transport properties of the DPP framework.

In this work, we designed and synthesized two similar π-conjugated molecules, -alkyl (DPP-R) and -aryl (DPP-B), to comparatively explore the S⋯π interactions using a scanning tunneling microscopy-based break junction (STM-BJ) technique. The conductance results of the STM-BJ experiments indicated that DPP-R has a 66% greater conductance () than DPP-B. Combined with molecular simulations, it was demonstrated that the presence of S⋯π interactions led to a certain degree of orbital overlap of the highest occupied molecular orbital (HOMO), and created a favorable channel for electron transport in the DPP-B junction.

Stabilization of Guest Molecules inside Cation-Lidded Cucurbiturils Reveals that Hydration of Receptor Sites Can Impede Binding.

Docking of alkali metal ions to water-soluble macrocyclic receptors generally reduces the affinity of guest molecules due to competitive binding. The idea that solvation water molecules could display a larger steric hindrance towards guest binding than cations has not been considered to date. We show that the docking of large cations to cucurbit[5]uril (CB5) unexpectedly increases (by a factor of 5-8) the binding of hydrophobic guests, methane and ethane.

Measurements of single-molecule electromechanical properties based on atomic force microscopy fixed-junction technique.

A hybrid technique combining atomic force microscopy and the fixed-junction technique is developed to simultaneously probe the electrical and mechanical characteristics of a single-molecule junction.

Dynamic Interconversions of Single Molecules Probed by Recognition Tunneling at Cucurbit[7]uril-Functionalized Supramolecular Junctions.

We introduce a versatile recognition tunneling technique using doubly cucurbit[7]uril-functionalized electrodes to form supramolecular junctions that capture analytes dynamically by host-guest complexation. This results in characteristic changes in their single-molecule conductance. For structurally related drug molecules (camptothecin, sanguinarine, chelerythrine, and berberine) and mixtures thereof, we observed distinct current switching signals related to their intrinsic conductance properties as well as pH-dependent effects which can be traced back to their different states (protonated versus neutral).

Mechanistic Investigation and Conductance Modulation of a Metal-Molecule-Metal Junction via Extra Acid Addition.

One important prerequisite for the fabrication of molecular functional device strongly relies on the understanding the conducting behaviors of the metal-molecule-metal junction that can respond to an external stimulus. The model Lewis basic molecule 4,4'-(pyridine-3,5-diyl)dibenzonitrile (DBP), which can react with Lewis acid and protic acid, was synthesized. Then, the molecular conducting behavior of DBP, DBP-B(C F ) , and DBP-TfOH (DBP-B(C F ) , and DBP-TfOH were produced by Lewis acid and protonic acid treatment of DBP) was researched and compared.

Developing Longer-Lived Single Molecule Junctions with a Functional Flexible Electrode.

Creating single-molecule junctions with a long-lived lifetime at room temperature is an open challenge. Finding simple and efficient approaches to increase the durability of single-molecule junction is also of practical value in molecular electronics. Here it is shown that a flexible gold-coated nanopipette electrode can be utilized in scanning tunneling microscope (STM) break-junction measurements to efficiently enhance the stability of molecular junctions by comparing with the measurements using conventional solid gold probes.

Detecting Individual Bond Switching within Amides in a Tunneling Junction.

Amides are essential in the chemistry of life. Detecting the chemical bond states within amides could unravel the nature of amide stabilization and planarity, which is critical to the structure and reactivity of such molecules. Yet, so far, no work has been reported to detect or measure the bond changes at the single-molecule level within amides.

Single-molecule conductance investigation of BDT derivatives: an additional pattern found to induce through-space channels beyond π-π stacking.

The through-space conductance of individual molecules is supposed to improve the macroscopic carrier movement, but the most widely acclaimed through-space conductance channel just existed in sufficiently close π-π stacked benzene rings. As a breakthrough to this primary cognition, additional conducting channels were confirmed to exist in non-strict face-to-face aligned thiophenes or phenyl-thiophene in BDT derivatives for the first time.

Cucurbituril mediated single molecule detection and identification via recognition tunneling.

Recognition tunneling (RT) is an emerging technique for investigating single molecules in a tunnel junction. We have previously demonstrated its capability of single molecule detection and identification, as well as probing the dynamics of intermolecular bonding at the single molecule level. Here by introducing cucurbituril as a new class of recognition molecule, we demonstrate a powerful platform for electronically investigating the host-guest chemistry at single molecule level.