Electron propagation through a molecular device is determined by its quantum electronic structure. We employ molecular conductance orbitals (MCOs) to predict and interpret quantum interference (QI), ...which contain more information about the electrodes compared with molecular orbitals (MOs) of an isolated molecule. The phases, amplitudes, and alignment of MCOs determine whether they interfere constructively or destructively, which can be seen directly from projection transmissions and QI maps. We apply this intuitive method to butadiene, benzene, and cyclopentadienyl (Cp) anion so that we can elucidate the mechanism of QI among the whole energy range beyond the Fermi level and demonstrate the unique characteristics of MCOs.
One of the key issues for the use of organic radicals in high-performance molecular electronic, spintronic and thermoelectric devices is the retention, at room temperature, of their open-shell ...character when they are in contact with the metal electrodes of a junction. By means of first-principles quantum transport calculations, we have investigated the stability and the electronic transport properties of single-molecule junctions incorporating a Blatter radical (BR) with thiomethyl linker groups. Our calculations suggest that the BR can unequivocally retain its open-shell nature even when bound to gold electrodes through undercoordinated gold adatoms. Such a state cannot be destroyed by the surrounding solvent molecules and the applied bias. The calculated low-bias conductance values of junctions with BR, an oxidized BR derivative, and a closed-shell stilbene molecule are in quantitative agreement with the available experimental measurements. The small conductance of the BR can be associated with the localization of its π-type singly occupied and singly unoccupied molecular orbitals (SOMO and SUMO), leading to an asymmetrically weak electronic coupling to the two gold electrodes, even though these two orbitals lie very close to the Fermi energy. Furthermore, the nonmonotonic modulation of the junction conductance controlled by a charge gate can be used in experiments to further verify the presence of the unpaired electron. This proof may be realized in practice with an electrostatic solid-state or an electrochemical gate. Our findings deepen the current understanding of the radical–metal interfacial properties and facilitate the design of future radical-based multifunctional molecular devices.
In single-molecule junctions, Fano resonance allows for efficient electron transport modulation between constructive and destructive interferences over a small energy range and can be exploited to ...increase the thermoelectricity and the sensitivity of single-molecule sensors. To explore the designing principles for Fano resonances, we have investigated the electronic transport properties of alkene- and naphthalene-based molecular junctions with molecular conductance orbitals (MCOs). A Fano resonance arises from the destructive quantum interference due to a pair of MCOs with opposite phases and comparable energies, for which one is more localized than the other. We introduce an asymmetry factor to distinguish the Fano resonances from other destructive quantum features. To increase the asymmetry factor, pendant groups coupled at the atomic site where the corresponding MCO has a zero coefficient can be employed to induce and modulate antiresonances.
The field of molecular assembly has seen remarkable advancements across various domains, such as materials science, nanotechnology, and biomedicine. Small gas molecules serve as pivotal modulators, ...capable of altering the architecture of assemblies via tuning a spectrum of intermolecular forces including hydrogen bonding, dipole–dipole interactions, and metal coordination. Surface techniques, notably scanning tunneling microscopy and atomic force microscopy, have proven instrumental in dissecting the structural metamorphosis and characteristic features of these assemblies at an unparalleled single-molecule resolution. Recent research has spotlighted two innovative approaches for modulating surface molecular assemblies with the aid of small gas molecules: “catassembly” and “coassembly”. This Perspective delves into these methodologies through the lens of varying molecular interaction types. The strategies discussed here for regulating molecular assembly structures using small gas molecules can aid in understanding various complex assembly processes and structures and provide guidance for the further fabrication of complex surface structures.
A novel coumarin Schiff base fluorescent probe ethyl 7-hydroxycoumarin-3-carboxylate-8-formaldehyde benzoyl hydrazone （EBH） has been designed and synthesized which shows solvent dependent dual ...sensing, viz., recognition of Ca^2＋ in DMF-H20 （9 ： 1, V/V） solution based on C=N isomerization, photoinduced electron transfer （PET） inhibition and chelation-enhanced fluorescence （CHEF） mechanism as well as detection of Zn^2＋ in HzO-CH3OH （9 ： 1, V/V） solution by excited-state intramolecular proton transfer （ESIPT） and CHEF processes. The structure of the probe EBH has been confirmed by single-crystal X-ray diffraction analysis. Meanwhile, the probe was also used to image intracellular Zn^2＋ ions in MCF-7 cells with a good performance.
