Spin-filter effect and spin-polarized optoelectronic properties in annulene-based molecular spintronic devices

Using Fe, Co or Ni chains as electrodes, we designed several annulene-based molecular spintronic devices and investigated the quantum transport properties based on density functional theory and non-equilibrium Green＇s function method.Our results show that these devices have outstanding spin-filter capabilities and exhibit giant magnetoresistance effect,and that with Ni chains as electrodes, the device has the best transport properties. Furthermore, we investigated the spinpolarized optoelectronic properties of the device with Ni electrodes and found that the spin-polarized photocurrents can be directly generated by irradiating the device with infrared, visible or ultraviolet light. More importantly, if the magnetization directions of the two electrodes are antiparallel, the photocurrents with different spins are spatially separated, appearing at different electrodes. This phenomenon provides a new way to simultaneously generate two spin currents.

High-performance spin-filtering and spin-rectifying effects in Blatter radical-based molecular spintronic device

We design a Blatter radical-based molecular spintronic device, and investigate its spin-polarized transport properties using density functional theory and non-equilibrium Green's function technique. High-performance spin-rectifying and spin-filtering effects are realized. The physical mechanism is explained by the spin-resolved bias voltage-dependent transmission spectra, the energy levels of the corresponding molecular projected self-consistent Hamiltonian orbitals, and their spatial distributions. The results demonstrate that the Blatter radical has great potential in the development of highperformance multifunctional molecular spintronic devices.

A Molecular Modeling for the Complexation of Cyclobis(paraquat-p-phenylene) with Substituted Benzenes and Biphenyls

Molecular orbital PM3 calculation was performed on the complexation of cyclobis(paraquat-p-phenylene) with a number of 1,4-disubstituted benzenes and biphenyl derivatives. A fair correlation was found between the PM3 calculated binding energies and the experimental ones, which enabled the PM3 calculation to predict thc experimental binding energies for a number of important complexes. A good structure-activity relationship was also found between the PM3 calculated binding energies and the substituent molar refraction R-m and Hammett constants. indicating that the van der Waals force and the electronic interactions constituted the major driving forces for the complexation of cyclobis(paraquat-p-phenylene).

The effects of contact configurations on the rectification of dipyrimidinyl-diphenyl diblock molecular junctions

The transport properties of a conjugated dipyrimidinyl-diphenyl diblock oligomer sandwiched between two gold electrodes, as recently reported by [Diez-Perez et al. Nature Chem. 1 635 （2009）], are theoretically investigated using the fully self-consistent nonequilibrium Green＇s function method combined with density functional theory. Two kinds of symmetrical anchoring geometries are considered. Calculated current-voltage curves show that the contact structure has a strong effect on the rectification behaviour of the molecular diode. For the equilateral triangle configuration, pronounced rectification behaviour comparable to the experimental measurement is revealed, and the theoretical analysis indicates that the observed rectification characteristic results from the asymmetric shift of the perturbed molecular energy levels under bias voltage. While for the tetrahedron configuration, both rectification and negative differential conductivity behaviours are observed. The calculated results further prove the close dependence of the transporting characteristics of molecular junctions on contact configuration.

The fabrication,characterization and functionalization in molecular electronics

Developments in advanced manufacturing have promoted the miniaturization of semiconductor electronic devices to a near-atomic scale,which continuously follows the‘top-down’construction method.However,huge challenges have been encountered with the exponentially increased cost and inevitably prominent quantum effects.Molecular electronics is a highly interdisciplinary subject that studies the quantum behavior of electrons tunneling in molecules.It aims to assemble electronic devices in a‘bottom-up’manner on this scale through a single molecule,thereby shedding light on the future design of logic circuits with new operating principles.The core technologies in this field are based on the rapid development of precise fabrication at a molecular scale,regulation at a quantum scale,and related applications of the basic electronic component of the‘electrode-molecule-electrode junction’.Therefore,the quantum charge transport properties of the molecule can be controlled to pave the way for the bottom-up construction of single-molecule devices.The review firstly focuses on the collection and classification of the construction methods for molecular junctions.Thereafter,various characterization and regulation methods for molecular junctions are discussed,followed by the properties based on tunneling theory at the quantum scale of the corresponding molecular electronic devices.Finally,a summary and perspective are given to discuss further challenges and opportunities for the future design of electronic devices.

Insights into electrolyte effects on photoactivities of dye-sensitized photoelectrochemical cells for water splitting

Dye-sensitized photoelectrochemical cell（DS-PEC） is an especially attractive method to generate hydrogen via visible light driven water splitting. Electrolyte, an essential component of DS-PEC, plays a great role in determining the photoactivities of devices for water splitting. When using phosphate buffer（pH = 6.4）as electrolyte, the DS-PEC displayed much higher photoactivity than using 0.1 M Na;SO;（pH = 6.4） as electrolyte. The insight is phosphate anion gathers together to form a negative electrostatic field on TiO;surface, which increases the resistance in the TiO;/catalyst and electrolyte interface and validly reduces the charge recombination from TiO;to the oxidized catalyst.

Conformational change-modulated spin transport at single-molecule level in carbon systems

Controlling the spin transport at the single-molecule level,especially without the use of ferromagnetic contacts,becomes a focus of research in spintronics.Inspired by the progress on atomic-level molecular synthesis,through firstprinciples calculations,we investigate the spin-dependent electronic transport of graphene nanoflakes with side-bonded functional groups,contacted by atomic carbon chain electrodes.It is found that,by rotating the functional group,the spin polarization of the transmission at the Fermi level could be switched between completely polarized and unpolarized states.Moreover,the transition between spin-up and spin-down polarized states can also be achieved,operating as a dual-spin filter.Further analysis shows that,it is the spin-dependent shift of density of states,caused by the rotation,that triggers the shift of transmission peaks,and then results in the variation of spin polarization.Such a feature is found to be robust to the length of the nanoflake and the electrode material,showing great application potential.Those findings may throw light on the development of spintronic devices.

Exploring how hydrogen at gold-sulfur interface affects spin transport in single-molecule junction

Very recently,experimental evidence showed that the hydrogen is retained in dithiol-terminated single-molecule junction under the widely adopted preparation conditions,which is in contrast to the accepted view[Nat.Chem.11351(2019)].However,the hydrogen is generally assumed to be lost in the previous physical models of single-molecule junctions.Whether the retention of the hydrogen at the gold-sulfur interface exerts a significant effect on the theoretical prediction of spin transport properties is an open question.Therefore,here in this paper we carry out a comparative study of spin transport in M-tetraphenylporphyrin-based(M=V,Cr,Mn,Fe,and Co;M-TPP)single-molecule junction through Au-SR and Au-S(H)R bondings.The results show that the hydrogen at the gold-sulfur interface may dramatically affect the spin-filtering efficiency of M-TPP-based single-molecule junction,depending on the type of transition metal ions embedded into porphyrin ring.Moreover,we find that for the Co-TPP-based molecular junction,the hydrogen at the gold-sulfur interface has no obvious effect on transmission at the Fermi level,but it has a significant effect on the spin-dependent transmission dip induced by the quantum interference on the occupied side.Thus the fate of hydrogen should be concerned in the physical model according to the actual preparation condition,which is important for our fundamental understanding of spin transport in the single-molecule junctions.Our work also provides guidance in how to experimentally identify the nature of gold-sulfur interface in the single-molecule junction with spin-polarized transport.

Device design based on the covalent homocouplingof porphine molecules

Porphine has a great potential application in molecular electronic devices.In this work,based on the density functional theory(DFT)and combining with nonequilibrium Green's function(NEGF),we study the transport properties of the molecular devices constructed by the covalent homocoupling of porphine molecules conjunction with zigzag graphene nanoribbons electrodes.We find that different couple phases bring remarkable differences in the transport properties.Different coupling phases have different application prospects.We analyze and discuss the differences in transport properties through the molecular energy spectrum,electrostatic difference potential,local density of states(LDOS),and transmission pathway.The results are of great significance for the design of porphine molecular devices in the future.

Gas-sensor property of single-molecule device:F_2 adsorbing effect

The single thiolated arylethynylene molecule with 9,10-dihydroanthracene core（denoted as TADHA） possesses pronounced negative differential conductance（NDC） behavior at lower bias regime. The adsorption effects of F2 molecule on the current and NDC behavior of TADHA molecular junctions are studied by applying non-equilibrium Green＇s formalism combined with density functional theory. The numerical results show that the F2 molecule adsorbed on the benzene ring of TADHA molecule near the electrode can dramatically suppresses the current of TADHA molecular junction. When the F2 molecule adsorbed on the conjugated segment of 9,10-dihydroanthracene core of TADHA molecule, an obviously asymmetric effect on the current curves induces the molecular system showing apparent rectifier behavior. However, the current especially the NDC behavior have been significantly enlarged when F2 addition reacted with triple bond of TADHA molecule.

Sub-nanometer supramolecular rectifier based on the symmetric building block with destructive σ-interference

Molecular rectifier, as a basic function of molecular electronic devices, has attracted extensive attention for the opportunity in constructing sub-nanometer electronic devices. However, tunneling leakage current has a significant contribution as electronic devices shrink in size, which leads to a challenge in fabricating molecular rectifiers at the sub-nanometer scale. Here, we experimentally demonstrate a sub-nanometer molecular rectifier based on the supramolecular junction assembled between water and 1,4-diazabicyclo[2.2.2]octane (DABCO) molecule. The charge transport through DABCO and corresponding supramolecular junctions exhibits destructive σ-interference, ensuring a sharp conductance variation for transmission modulation. The supramolecular interaction between DABCO and water readily introduces the asymmetric electrode-molecule interaction, which combines with the destructive σ-interference to support the sub-nanometer rectification.

Molecular-scale electronics： From device fabrication to functionality

By wiring molecules into circuits, ＂molecular electronics＂ aims at studying electronic properties of single molecules and their ensembles, on this basis exploiting their intrinsic functionalities, and eventually applying them as building blocks of electronic components for future electronic devices. Herein, fabricating reliable solid-state molecular devices and developing synthetic molecules endowed with desirable electronic properties, have been two major tasks since the dawn of molecular electronics. This review focuses on recent advances and efforts regarding the main challenges in this field, highlighting fabrication of nanogap electrodes for single-molecule junctions, and self-assembled-monolayers （SAMs） for functional devices. The prospect of molecular-scale electronics is also discussed.

Local Energy Dissipation/Transition in Field Effect Molecular Nanoelectronic Systems:a Quantum Mechanical Methodology

Electronic and vibrational intra-molecular thermoelectric-like ?gures of merit(ZT_γ~M) are introduced for single molecule nanoelectronic system, using quantum theory of atoms in molecule. These ?gures of merit are used to describe intra-molecular or local energy dissipation/transition(as in Joule-like, Peltier-like, and Thomson-like effects) in?eld effect molecular devices. The ZT_γ~M?gures of merit are computed for two proposed molecular devices. Analysis of the results shows that ZT_γ~Mdepends almost non-linearly on the electric ?eld(EF) strength. Also, the intra-molecular Joule-like heating plays a dominant role in the local energy dissipation, and intra-molecular Thomson-like heating is generally larger than the intra-molecular Peltier-like heating. Introduction of ZT_γ~Mcan be applied to extend the analysis of thermoelectric heating down to molecular and intra-molecular levels, and thus can be used to predict characteristics and performance of any candidate multi-terminal or multi-pole molecular systems prior to their application in real nanoelectronic circuits.

Deep Ultraviolet Phototransistor Based on Thiophene-Fluorobenzene Oligomer with High Mobility and Performance

Deep ultraviolet(UV)photodetectors have important applications in the industrial and military fields.However,little research has been reported on organic phototransistors(OPTs)in the deep ultraviolet range.Here,a novel organic semiconductor containing a small torsion angle and lowπ-conjugation 2,2':5',2"-terthiophene groups,oF-PTTTP,is designed and synthesized,which exhibits high carrier mobility and unique deep ultraviolet response.Accordingly,an OPT based on oF-PTTTP single crystal shows high responsivity to deep-UV light.The photodetectors achieve high photoresponsivity(R)of 857 A/W and detectivity(D*)of 3.2×10^(15)Jones under 280 nm light illumination(only 95 nW·cm^(–2)).To the best of our knowledge,280 nm is the deepest detection wavelength reported for organic phototransistors and this work presents a new molecule design concept for organic phototransistors with deep-UV detection.

Electron Transport through Hydrogen Bonded Single-Molecule Junctions

Hydrogen bonding is a vital driving force for organizing the hierarchy of molecular structure,especially in biologic field.Due to its directionality,selectivity and moderate strength,hydrogen bonding has been extensively introduced into the molecular recognition,sensing and electronic devices.Electric measurements at single-molecule level facilitate the investigation of hydrogen bonds and provide a comprehensive understanding of the electron transport properties governed by the hydrogen bonding,which is essential for the development of self-assembled electronic systems.This review provides a detailed overview of recent advancements in constructing single-molecule junctions utilizing intramolecular and intermolecular hydrogen bonding.We first introduce the methods utilized for characterizing the electric and dynamic properties of non-covalent interactions.Next,we discuss the mechanisms of electron transport,relevant influencing factors,and typical applications utilizing electrical signals based on single-molecule junctions.Finally,we propose our perspective on the existing challenges and prospective opportunities in utilizing hydrogen bonding for electronic device applications.

Azulene-based organic functional molecules for optoelectronics

Design and synthesis of new organic functional materials with improved performance or novel properties are of great importance in the field of optoelectronics.Azulene,as a non-alternant aromatic hydrocarbon,has attracted rising attention in the last few years.Different from most common aromatic hydrocarbons,azulene has unique characteristics,including large dipole moment,small gap between the highest occupied molecular orbital（HOMO） and the lowest unoccupied molecular orbital（LUMO）.However,the design and synthesis of azulene-based functional materials are still facing several challenges.This review focuses on the recent development of organic functional materials employing azulene unit.The synthesis of various functionalized azulene derivatives is summarized and their applications in optoelectronics are discussed,with particular attention to the fields including nonlinear optics（NLO）,organic field-effect transistors（OFETs）,solar cells,and molecular devices.

Towards Responsive Single-Molecule Device

Single-molecule devices,which are fabricated by the single molecule bridged through electrodes,provide a promising approach to investigate the intrinsic chemical or physical properties of individual molecules.Beyond the studies of single-molecule wires,a large number of responsive single-molecule junctions or devices with unique chemical or physical properties have been designed and fabricated by introducing the external field,which further offers the chance to explore conductive materials at the molecular level.Here,we summarized the latest studies on the behaviors of single-molecule devices based on the photon,thermal,electric,or magnetic responses,and discussed the development of responsive single-molecule devices in prospect.

Atomic and Close-to-Atomic Scale Manufacturing:A Review on Atomic Layer Removal Methods Using Atomic Force Microscopy

Manufacturing at the atomic scale is the next generation of the industrial revolution.Atomic and close-to-atomic scalemanufacturing(ACSM)helps to achieve this.Atomic force microscopy(AFM)is a promising method for this purposesince an instrument to machine at this small scale has not yet been developed.As the need for increasing the number ofelectronic components inside an integrated circuit chip is emerging in the present-day scenario,methods should be adoptedto reduce the size of connections inside the chip.This can be achieved using molecules.However,connecting moleculeswith the electrodes and then to the external world is challenging.Foundations must be laid to make this possible for thefuture.Atomic layer removal,down to one atom,can be employed for this purpose.Presently,theoretical works are beingperformed extensively to study the interactions happening at the molecule-electrode junction,and how electronic transportis affected by the functionality and robustness of the system.These theoretical studies can be verified experimentally only if nano electrodes are fabricated.Silicon is widely used in the semiconductor industry to fabricate electronic components.Likewise,carbon-based materials such as highly oriented pyrolytic graphite,gold,and silicon carbide find applications inthe electronic device manufacturing sector.Hence,ACSM of these materials should be developed intensively.This paperpresents a review on the state-of-the-art research performed on material removal at the atomic scale by electrochemical andmechanical methods of the mentioned materials using AFM and provides a roadmap to achieve effective mass productionof these devices.

Synthesis and Opto-electronic Properties of a Red-Emitting Heteroleptic Platinum Complex Using Pyrazol-based Diketone Derivative as Ancillary Ligand

A red-emitting heteroleptic cyclometalated platinum（II） complex containing an ancillary ligand of pyra- zol-based diketone derivative was synthesized. Its optophysical and electroluminescent properties were studied. Compared to the reported （piq）Pt（acac） complex, this platinum（II） complex exhibited a blue-shifted UV absorption band at 300--450 nm, a low LUMO energy level and improved electroluminescent property. Using this platinum（II） complex as a single doping emitter and a blend of ploy（9,9-dioctylfluorene） and 2-tert-butylphenyl-5-phenyl- 1,3,4-oxadiazole as a host matrix, the fabricated polymer light-emitting devices displayed saturated red emission with a peak at 648 um and a shoulder at 601 nm. Furthermore, the emission quenching of the platinum（II） complex was significantly suppressed in these devices at high current density due to an introduction of the non-planar pyra- zol group into the ancillary ligand.

Information gathering and processing with fluorescent molecules

Molecular information gathering and proces- sing -- a young field of applied chemistry -- is undergoing good growth. The progress is occurring both in terms of conceptual development and in terms of the strengthening of older concepts with new examples. This review critically surveys these two broad avenues. We consider some cases where molecules emulate one of the building blocks of electronic logic gates. We then examine molecular emulation of various Boolean logic gates carrying one, two or three inputs. Some single-input gates are popular information gathering devices. Special systems, such as ＇lab-on-a-molecule＇ and molecular key- pad locks, also receive attention. A situation deviating from the Boolean blueprint is also discussed. Some pointers are offered for maintaining the upward curve of the field.