1,3-diphenyltriazene as a possible optical molecular switch: A first-principles study

By applying nonequilibrium Green's function formalism combined with first-principles density functional theory, we investigate the electronic transport properties of a 1,3-diphenyltriazene-based optical molecular switch. The molecule that comprises the switch can convert between the cis and the trans forms upon photoexcitation. The transmission spectra of two forms are remarkably distinctive. Theoretical results show that the current through the trans form is significantly larger than that through the cis form, which suggests that this system has attractive potential application in future molecular switch technology.     

A possible salicylideneanilines-based optical molecular switch induced by a reversible hydrogen transfer: an ab initio study

The electronic transport properties of the salicylideneanilines-based molecular optical switch are investigated using a nonequilibrium Green's function formalism combined with first-principles density functional theory. The molecule that comprises the switch can convert between the enol and keto tautomeric forms upon photoinduced excited state hydrogen transfer in the molecular bridge. Theoretical results show that the current through the enol form is significantly larger than that through the keto form, which realize the on and off states of the molecular switch. The physical origin of the switching behaviour is interpreted based on the spatial distributions of molecular orbitals and the HOMO-LUMO gap. Furthermore the effect of the donor/acceptor substituent on the electronic transport through the molecular device is also discussed in detail. The switching performance can be improved to some extent through the acceptor substituent.     

Switching behavior induced by different substituents of group in single molecular device

We investigate the electronic transport properties of photochromic azobenzene-based molecular devices with Au electrodes using non-equilibrium Green’s function and density functional theory. A reversible switching behavior between cis and trans isomerization is found in the device. In addition, the substituent of ?NH₂ on the right end hydrogen atom of azobenzene molecule reduces the switching ratio of current, consequently the disappearance of switching behavior, while the substituent of ?NO₂ improves the switching ratio of current. We discuss the different electronic transport induced by different substituents through the transmission spectra, localized density of states, molecular projected self-consistent Hamiltonian and transmission pathways. The observed polarization effect under bias is explained by the evolution of molecular projected self-consistent Hamiltonian of LUMO level. The results indicate that the electron-withdrawing group ?NO₂ substituting right terminal hydrogen of azobenzene molecule becomes a candidate for improving the performance of molecular device.     

First-principles study of the electronic transport properties of the anthraquinone-based molecular switch

By applying non-equilibrium Green’s function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.     

Current–Voltage Characteristics of the Aziridine-Based Nano-Molecular Wires: a Light-Driven Molecular Switch

Using nonequilibrium Green's function formalism combined first-principles density functional theory, we analyze the transport properties of a 4,4-dimethyl-6-(4-nitrophenyl)-2-phenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene molecular optical switch. The title molecule can convert between closed and open forms by visible or ultraviolet irradiation. The I-V characteristics, differential conductance, on-off ratio, electronic transmission coefficients, spatial distribution of molecular projected self-consistent Hamiltonian orbitals, HOMO-LUMO gaps, effect of electrode materials Y(111)(Y =Au, Ag and Pt) on electronic transport and different molecular geometries corresponding to the closed and open forms through the molecular device are discussed in detail. Based on the results, as soon as possible the open form translates to the closed form, and there is a switch from the ON state to the OFF state(low resistance switches to high resistance). Theoretical results show that the donor/acceptor substituent plays an important role in the electronic transport of molecular devices. The switching performance can be improved to some extent through suitable donor and acceptor substituents.     

Coherent electron transport through an azobenzene molecule: a light-driven molecular switch

We apply a first-principles computational approach to study a light-sensitive molecular switch. The molecule that comprises the switch can convert between a trans and a cis configuration upon photoexcitation. We find that the conductance of the two isomers varies dramatically, which suggests that this system has potential application as a molecular device. A detailed analysis of the band structure of the metal leads and the local density of states of the system reveals the mechanism of the switch.     

Electronic transport properties of a diarylethene-based molecular switch with single-walled carbon nanotube electrodes: The effect of chirality

We have studied the electronic transport properties of an optical molecular switch based on the diarylethene molecule with two single-walled carbon nanotube (SWCNT) electrodes using first-principles transport calculations. It is shown that the closed form shows an overall higher conductance than the open form at low bias which is independent of the SWCNTs’ chirality. Meanwhile, the conductance of the molecular switch can be tuned by changing the chirality of the SWCNTs.     

顺、反聚噻咯的电子结构和光谱性质的比较研究

用密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）对聚合度为2-7的线型反式聚噻咯（1a-6a）与顺式聚噻咯（1b-6b）的电子结构和吸收光谱进行了比较计算。在获得基态稳定构型的基础上,进行了自然键轨道（NBO）分析,随后计算了各体系的电子吸收光谱。结果发现,随着聚合度的增大,顺式和反式聚噻咯的结构稳定性均增强,最大吸收波长均发生红移,并且顺式结构红移更明显。此研究为聚噻咯应用在空穴传输材料、导电材料、发光二极管等发光材料领域提供了理论依据。     

Steady-state fluorescence and photo-isomerization study of 1-methyl-4′-(p-N,N dimethyl-amino styryl) pyridinium iodide

Photochemical and thermal trans/cis isomerization reactions are reported for 1-methyl-4′-(p-N,N dimethyl-amino styryl) pyridinium iodide, Cy, which is synthesized in the trans configuration. In a basic solution the trans form, Cy_tr, cannot isomerise directly to the cis form. Its protonated form, Cy_trH⁺, is active and reacts photochemically from trans to cis isomer, Cy_cH⁺. The quantum yields Φ_tc and Φ_ct are determined in water. Deprotonation process of Cy_cH⁺ yields the cis isomer, Cy_c, which can thermally revert to the stable trans form. The rate constant and the activated parameters of the thermal reaction are also determined. Due to irreversibility of the thermal reaction , a complete molecular reaction cycle is performed in one direction. To get more information on the spectral properties of protonated form, its absorption and fluorescence spectra were investigated in sixteen neat polar protic and aprotic solvents. Absorption energy correlates linearly with hydrogen bond acceptor ability of the solvent. Another linear correlation was found between fluorescence energy of CyH⁺ and free energy for transferring the proton to the surrounding solvent, ΔG_t^o.     

The Studies of 13C NMR Chemical Shifts and Induced Lanthanide Shift Reagent Cis-trans Isomerization of N-Cinamylidene-hexyl,t-butyl and Substituted Aryl-Amines

The Carbon-13 chemical shifts of N-Cinamylidenehexyl, t-butyl and sixteen substituted aryl amines were analysed. The lanthanide induced carbon-13 chemical shifts of the cis and trans of four N-cinamylidene substituted anilines were analysed. The spectra N-cinamylidene hexylamine showed only the trans form. The cis/trans ratio of N-cinamylidene aryl amines increased as the LSR concentration increased.     

Microwave Spectrum and Conformation in 2-Fluorophenylisothiocyanate

The microwave rotational spectra of 2-fluorophenylisothiocyanate have been investigated in the frequency region of 26.0-38.0 GHz. Analysis of a-type R-branch transitions confirmed the existence of two conformers: cis and trans. Rotational and centrifugal distortion constants for both conformers have been derived. The observed inertial defect values demonstrate their planarity. From the relative intensity ratio the cis form was shown to be more stable than the trans form by about 208 cm(-1). Finally, molecular geometries for both conformers have been proposed. Copyright 2000 Academic Press.     

Theoretical investigation on surface‐enhanced Raman evidence for conformation transition of dimercaptoazobenzene adsorbed on gold nanoclusters

Probing and controlling the configurations and mechanical motions of the azobenzenes adsorbed on the metal substrates are preliminary for their applicability in various functional devices. In this work, we presented a detailed investigation of Raman properties of the dimercaptoazobenzene (DMAB) bound to gold nanoclusters using density functional calculations. It is demonstrated that the spectral features of the trans conformation of DMAB are quite different from the cis conformation, and the Raman intensities of the trans‐DMAB are much larger. Magnitude of chemical enhancement for the adsorbed trans‐DMAB is found to be close to or less than that for the adsorbed cis‐DMAB for the molecule–cluster complexes. This change trend can be, to a large extent, governed by the energy difference between the highest occupied energy level of the molecule and the lowest unoccupied energy level of the gold. Moreover, it is further demonstrated that differences in Raman intensities of the two conformations can be amplified for the cluster–molecular–cluster junctions, and thus chemical enhancement is much larger for the trans conformation than the cis conformation, possibly facilitating the experimental identification of the trans/cis DMAB. Copyright © 2012 John Wiley & Sons, Ltd.     

CNDO calculations of some thioamides—II

CNDO calculation is made for thioformamide, N-methylthioformamide (both in cis and trans forms) and N, N-dimethyl thioformamide. The charges, bond orders, dipolemoments and ionization potentials of molecules are discussed and comparison made with corresponding amides. The barrier to internal rotation about C-N bond for thioformamide and N-chloroacetamide is reported along with changes in the charges on atoms and dipolemoment of molecules with rotation. The trans form of N-methyl thioformamide is found to be more stable than cis isomer by 4.9 Kcal/mole.     

Thermal cis–trans isomerization of triazo-benzene

1,3,5-Hydroxy-triazo-benzene (H-TAB) was synthesized through a coupling-oxidation protocol. Temperature-controlled UV, IR, and ab initio calculation were carried out to investigate the cis–trans thermal isomerization of H-TAB. In temperature-controlled UV experiments, λ_max of the π–π¹ band and for the trans conformation at 335 nm and that for the cis form at 282 nm are shifted by increased temperature; band intensities of the π–π¹ transition decrease and λ_max of the π–π¹ band is shifted toward the high-energy region. The maximum peak at 2922 cm⁻¹ is shifted to 2926 cm⁻¹, and that at 2852 cm⁻¹ is shifted to 2856 cm⁻¹ at increased temperature in the temperature-controlled IR experiment. Ab initio calculation reveals that the cis conformation of H-TAB is more stable than the trans form because the cis form has less spatial repulsion. Therefore, the ground-state energy difference induced by steric repulsion of the benzene unit is the driving force of the blue shift in the thermal IR and UV spectra for the triazo-benzene.     

Influence of edge passivation on the transport properties of the zigzag phosphorene nanoribbons

By using first-principles calculation based on density functional theory and non-equilibrium Green's function method, we investigate the transport properties of zigzag phosphorene nanoribbons (ZPNRs). The edges of the ZPNRs can be passivated in three ways named W1, W2, W3. These calculated results show that the electronic transport properties of the ZPNRs can be seriously influenced by the edge passivation ways, and the transport is determined by both the two edges and the interaction between them. Moreover, we find the width of the ZPNR can switch on or switch off the transport channel of the W3-type ZPNR. Furthermore, we present the transmission spectra, the band structures of both left and right electrodes, the molecular energy levels, and transmission eigenstates of the H-S-passivated W3-type ZPNRs to uncover the transport mechanism. This study provides a theoretical support for designing the related nanodevices by changing the passivation ways, which is an effective route for tuning the electronic structures and the transport properties of the phosphorene nanoribbons.     

Effect of carbon nanotubes chirality on the E–C photo-isomerization switching behavior in moelcular device

Applying nonequilibrium Green's function formalism in combination with the first-principles density functional theory, we investigate the electronic transport properties of optical molecular switch based on the fulgide molecule with two different single-walled carbon nanotube (SWCNT) electrodes. The molecule that comprises the switch can convert between E isomer and C isomer by ultraviolet or visible irradiation. Theoretical results show that these two isomers exhibit very different conductance properties both in armchair and zigzag junction, which can realize the on and off states of the molecular switch. Meantime, the chirality of the SWCNT electrodes strongly affects the switching characteristics of the molecular junctions, which is useful for the design of functional molecular devices.     

用1H-NMR-Eu (fod)3位移谱研究3-(2,2,2-三氯乙烯基)-2,2-二甲基环丙烷羧酸甲酯的立体构型

本文用¹H-NMR-Eu （fod）₃位移谱鉴定了(1RS)-3-(2,2,2-三氯乙烷基)-2,2-二甲基环丙烷羧酸甲酯的顺、反异构体,测出其三元碳环质子的耦合常数³J=5.5Hz (顺式)、4Hz (反式),并以此确定构型。根据质子极限位移的测定值与假接触位移公式,求出两种配位物合理的配位参数,并由此计算出其顺、反异构体的羰基与Eu（fod）₃配位能力的比值。     

Effect of Chirality on the Electronic Transport Properties of the Thioxanthene-Based Molecular Switch

Based on the nonequilibrium Green function method and density functional theory calculations,we theoretically investigate the effect of chirality on the electronic transport properties of thioxanthene-based molecular switch.The molecule comprises the switch which can exhibit different chiralities,that is,cis-form and trans-form by ultraviolet or visible irradiation.The results clearly reveal that the switching behaviors can be realized when the molecule converts between cis-form and trans-form.Furthermore,the on-off ratio can be modulated by the chirality of the carbon nanotube electrodes.The maximum on-off ratio can reach 109 at 0.4 V for the armchair junction,suggesting potential applications of this type of junctions in future design of functional molecular devices.     

Rotational barrier and thermodynamical parameters of furfural,thiofurfural, and selenofurfural in the gas and solution phases: theoretical study based on density functional theory method

This work aims to study the trans and cis conformers of furfural, thiofurfural and selenofurfural in the gas and solution phases. Assuming that there is equilibrium between these conformers, the transition state has also been investigated. All computations have been done using density functional theory method with B3LYP as the functional and 6-311++G(d,p) as the basis sets. The optimized molecular structures and related parameters of these conformers are reported. The infrared wavenumbers and Raman activities of these conformers are also reported with appropriate assignments. The energy differences between the trans and cis conformers, associated barriers and thermodynamical parameters have been derived from the computations. It is found that the structural parameters are not much different in the gas and solution phases. However, in the gas phase, the trans conformer is always more stable, but increasing the polarity of the solvent leads to the cis conformer becoming more stable. The rotational barrier is always larger than the energy difference and both of them increase when the solvent becomes more polar. Some of the results for furfural compare satisfactorily with literature and therefore the data from this work will be useful for thiofurfuraldehyde and selenofurfuraldehyde, as their literature is limited.     

Transport properties of graphene functionalized with molecular switches

We provide a theory of the electronic transport properties of a graphene layer functionalized with molecular switches. Our considerations are motivated by the spiropyran-merocyanine system which is non-polar in its ring-closed spiropyran form and zwitterionic in its ring-open merocyanine form. The reversible switching between these two isomers affects the carriers in graphene through the associated change in the molecular dipole moment, turning the graphene layer into a sensor of the molecular switching state. We present results for both the quasiclassical (Boltzmann) and the quantum coherent regimes of transport. Quite generally, we find a linear sensitivity of the conductance on the molecular dipole moment whenever quantum interference effects play an essential role which contrasts with a quadratic (and typically weaker) dependence when quantum interference is absent.