Biphenyldithiol Research Articles

Raman Monitoring of the Electro-Optical Synergy-Induced Enhancements in Carbon-Bromine Bond Cleavage, Reaction Rate, and Product Selectivity of p-Bromothiophenol.

Electro-optical synergy has recently been targeted to improve the separation of hot carriers and thereby further improve the efficiency of plasmon-mediated chemical reactions (PMCRs). However, the electro-optical synergy in PMCRs needs to be more deeply understood, and its contribution to bond dissociation and product selectivity needs to be clarified. Herein, the electro-optical synergy in plasmon-mediated reduction of p-bromothiophenol (PBTP) was studied on a plasmonic nanostructured silver electrode using in situ Raman spectroscopy and theoretical calculations. It was found that the electro-optical synergy-induced enhancements in the cleavage of carbon-bromine bonds, reaction rate, and product selectivity (4,4'-biphenyl dithiol vs thiophenol) were largely affected by the applied bias, laser wavelength, and laser power. The theoretical simulation further clarified that the strong electro-optical synergy is attributed to the matching of energy band diagrams of the plasmonic silver with those of the adsorbed PBTP molecules. A deep understanding of the electro-optical synergy in PBTP reduction and the clarification of the mechanism will be highly beneficial for the development of other highly efficient PMCRs.

Analysis of molecular ligand functionalization process in nano-molecular electronic devices containing densely packed nano-particle functionalization shells

Molecular electronic devices based on few and single-molecules have the advantage that the electronic signature of the device is directly dependent on the electronic structure of the molecules as well as of the electrode-molecule junction. In this work, we use a two-step approach to synthesise functionalized nanomolecular electronic devices (nanoMoED). In first step we apply an organic solvent-based gold nanoparticle (AuNP) synthesis method to form either a 1-dodecanethiol or a mixed 1-dodecanethiol/ω-tetraphenyl ether substituted 1-dodecanethiol ligand shell. The functionalization of these AuNPs is tuned in a second step by a ligand functionalization process where biphenyldithiol (BPDT) molecules are introduced as bridging ligands into the shell of the AuNPs. From subsequent structural analysis and electrical measurements, we could observe a successful molecular functionalization in nanoMoED devices as well as we could deduce that differences in electrical properties between two different device types are related to the differences in the molecular functionalization process for the two different AuNPs synthesized in first step. The same devices yielded successful NO2 gas sensing. This opens the pathway for a simplified synthesis/fabrication of molecular electronic devices with application potential.

Electrochemically activated carbon-halogen bond cleavage and C-C coupling monitored by in situ shell-isolated nanoparticle-enhanced Raman spectroscopy.

The electroreductive cleavage of carbon-halogen bonds has attracted increasing attention in both electrosynthesis and pollution remediation. Herein, by employing the in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique, we have successfully investigated the electroreductive dehalogenation process of aryl halides with the thiol group on a smooth Au electrode in aqueous solution at different pH values. The obtained potential-dependent Raman spectra directly reveal a mixture of the reduction products 4,4'-biphenyldithiol (BPDT) and thiophenol (TP). The conversion ratios of the C-Cl and C-Br bonds at pH = 7 are 37% and 55%, respectively. Furthermore, quantitative analysis of the intensity variations of ν(C-Cl), ν(C-Br) and aromatic ν(CC) stretching modes suggests electroreductive dehalogenation via both direct electron transfer reduction and electrocatalytic hydrodehalogenation. Molecular evidence for the C-C cross coupling process through TP reaction with benzene free radical intermediates is found at negative potentials, which leads to the increasing selectivity of biphenyl products.

Examining conductance values in the biphenyl molecular switch with reduced density matrices

AbstractElectronic switches built from single molecules such as biphenyl dithiol are promising replacements for traditional electronic devices. To support experimental investigations of molecular switches, charge transport values are typically predicted using non‐equilibrium Green's functions constructed using density functional theory (NEGF‐DFT). Previous studies of biphenyl dithiol, however, have usually overestimated experimental conductance values and have not reproduced a drop in conductance at low torsional angles. In this paper, we employ a methodology that constructs the non‐equilibrium Green's functions from 2‐electron reduced density matrix theory (NEGF‐RDM). This approach has previously predicted lower conductance values than NEGF‐DFT for systems where NEGF‐DFT is known to overestimate transport. In the first direct comparison of the NEGF‐RDM method and experimental results, we examine the biphenyl dithiol at a range of torsional angles. We evaluate both the quantitative accuracy of multiple NEGF methods and provide insights into the experimentally observed drop in conductance at small torsional angles.

Probing adhesive interactions of self-assembled monolayers of Biphenyldithiol on Au(111): molecular dynamics simulation of force-distance measurements in atomic force microscopy

ABSTRACT This paper presents an investigation of atomic force microscopy (AFM) in the force-distance mode for self-assembled monolayers (SAM) by means of molecular dynamics modeling methods. A model system of SAM of biphenyldithiol (BPDT) on a gold substrate and a gold tip with a diameter of 10 nm were used. This work has reproduced the general behavior of force–distance curves in similar systems observed in experimental studies. The impact of the structural order (i.e., standing up ordered, disordered and striped phases) on the attractive and repulsive molecular interactions and conformations were revealed. The ordered SAM in standing up phase has the highest adhesive force and the striped phase has the lowest. The adhesive forces as a function of the tip-surface distance exhibit some unique and distinct features. An AFM induced ordering for both disordered and striped phases is reported.

Nanomolecular electronic devices based on AuNP molecule nanoelectrodes using molecular place-exchange process

The implementation of electronics applications based on molecular electronics devices is hampered by the difficulty of placing a single or a few molecules with application-specific electronic properties in between metallic nanocontacts. Here, we present a novel method to fabricate 20 nm sized nanomolecular electronic devices (nanoMoED) using a molecular place-exchange process of nonconductive short alkyl thiolates with various short chain conductive oligomers. After the successful place-exchange with short-chain conjugated oligomers in the nanoMoED devices, a change in device resistance of up to four orders of magnitude for 4,4′-biphenyldithiol (BPDT), and up to three orders of magnitude for oligo phenylene-ethynylene (OPE), were observed. The place-exchange process in nanoMoEDs are verified by measuring changes in device resistance during repetitive place-exchange processes between conductive and nonconductive molecules and surface-enhanced Raman spectroscopy. This opens vast possibilities for the fabrication and application of nanoMoED devices with a large variety of molecules.

Reply to the 'Comment on "Quantum interference effects in biphenyl dithiol for gas detection"' by A. Grigoriev, H. Jafri and K. Leifer, RSC Adv., 2020, 10, DOI: 10.1039/C9RA00451C.

The Comment on our publication [Prasongkit et al., RSC Adv., 2016, 64, 59299] is puzzling since it is well known that biphenyl is fairly non-reactive. Hence, it's not surprising we have low binding energies when the gas molecules were adsorbed on biphenyl dithiol (BPDT). The large binding energy of NO2 chemisorbed onto BPDT (∼2.04 eV) in the Comment conflicts with existing theoretical and experimental evidence. Grigoriev et al. have attempted to compare their results to our findings, employing different approximation schemes under the density functional theory (DFT) framework. Here, the effect of taking into account van der Waals (vdW) interactions upon the adsorption mechanism of small aromatic molecules has been discussed.

Comment on "Quantum interference effects in biphenyl dithiol for gas detection" by J. Prasongkit and A. R. Rocha, RSC Adv., 2016, 64, 59299-59304.

The paper [Prasongkit et al., RSC Adv., 2016, 64, 59299] by Prasongkit and Rocha calculates the binding energy of gas molecules attached to 1-8-biphenyl-dithiol (BPDT) molecules. We find from our calculations, that the binding energies calculated for the NO2 molecules are too low, most likely due to lacking optimization of the site at which the gas molecule binds to the BPDT. Though not shown explicitly here, the same statement might apply to the other gas molecules used in this paper.

Quantum and Phonon Interference-Enhanced Molecular-Scale Thermoelectricity.

Simultaneous engineering of electron and phonon transport through nanoscale molecular junctions is fundamental to the development of high-performance thermoelectric materials for the conversion of waste heat into electricity and cooling. Here, we demonstrate a systematic improvement of the room-temperature thermoelectric figure of merit (ZT) of molecular junctions. This is achieved by phonon interference (PI)-suppressed thermal conductance and quantum interference-enhanced electrical conductance and Seebeck coefficient. This strategy leads to a significant enhancement of ZT from low values ca. 10–6 in oligo(phenylene-ethynylene) (OPE2) to the record values of 2.4 in dinitro-functionalized OPE2 (DOPE2). The dinitro functionalization also considerably enhances ZT of biphenyl-dithiol (BDT) and bipyridyl molecular junctions. Remarkably, the energy levels of electron-withdrawing nitro groups are hardly changed from one molecule to the other. Because of this generic feature, a resonance transport in the vicinity of Fermi energy of electrodes is formed leading to a significant improvement of Seebeck coefficient and ZT of all derivatives. For example, the Seebeck coefficient enhances from 10.8 μV/K in BDT to −470 μV/K in dinitro-BDT (DBDT). In addition, destructive PI due to the nitro groups suppresses phonon thermal conductance, for example, from 20 pW/K in BDT to 11 pW/K in DBDT at room temperature. We also demonstrate that quantum and PI-enhanced single-molecule thermoelectric efficiency is conserved when parallel molecules are placed between gold electrodes. These results promise to remove the key roadblocks and open new avenues to exploit functionalized organic molecules for thermoelectric energy harvesting and cooling.

Synthesis of Network Polymers from Multifunctional Aromatic Thiol Compounds

Network polymers have been synthesized by means of catalyst free thiol-yne reaction of multi-functional aromatic ethynyle and thiol compounds, 1,3,5-triethynylbenzenen (TEB), 1,4-diethynylbenzene (DEB), 1,4-benzenedithiol (BDT) and benzenethiol (BT). The network polymers of TEB/DEB-BDT or TEB-BDT/BT were obtained in good yields. The feed ratio of DEB or BT increased the chloroform solution, fragments, of the network polymers. The fragments of the network polymers showed optical properties derived from conjugation units of phenyl-ethynyl-sulfide. The network polymers have been synthesized by oxidation reaction of multi-functional aromatic thiol compounds, 1,3,5-benzene trithiol (BTT) with BDT or 4,4’-biphenyl dithiol (BPDT), accompanied by formation of disulfide bonds. The BTT network was degradable by a reductant, tris(2-caboxyethyl)phosphine hydrochloride.

A sub 20 nm metal-conjugated molecule junction acting as a nitrogen dioxide sensor.

The interaction of a gas molecule with a sensing material causes the highest change in the electronic structure of the latter, when this material consists of only a few atoms. If the sensing material consists of a short, conductive molecule, the sensing action can be furthermore probed by connecting such molecules to nanoelectrodes. Here, we report that NO2 molecules that adhere to 4,4'-biphenyldithiol (BPDT) bound to Au surfaces lead to a change of the electrical transmission of the BPDT. The related device shows reproducible, stable measurements and is so far the smallest (<20 nm) gas sensor. It demonstrates modulation of charge transport through molecules upon exposure to nitrogen dioxide down to concentrations of 55 ppb. We have evaluated several devices and exposure conditions and obtained a close to linear dependence of the sensor response on the gas concentration.

Quantum interference effects in biphenyl dithiol for gas detection

Biphenyl dithiol (BPDT) was examined for the detection of NO, NO2, NH3 and CO gas molecules using the first-principle methods. The quantum interference effects were observed in the transmission, revealing the application of BPDT as a gas sensor.

Interaction of Graphene with Self Assembled Monolayers

SummaryThe adsorption of graphene onto solid surface is vital for the numerous device applications. In the present work, we studied interaction of graphene with chemically modified surfaces. We formed the self‐assembled monolayers (SAM) of octadecanethiol (ODT), mercapto undecanoic acid (MUA) and biphenyl dithiol (BPD) onto the gold substrates. The nature of the surfaces obtained for ODT and MUA were hydrophobic and hydrophilic, respectively. The SAM of BPD yields the surface with phenyl rings having delocalized π‐electrons. Due to hydrophobic nature of the graphene, it adsorbs onto the SAMs of ODT and BPD. The surface morphology of the graphene onto SAMs was studied using atomic force microscope. Due to π−π stacking interaction between the graphene and BPD molecules, graphene prefers planar adsorption onto the SAM of BPD. The hydrophobic interaction between the graphene and ODT leads to random and non‐uniform adsorption of graphene onto the SAM of ODT. Surface plasmon resonance (SPR) phenomenon is extremely sensitive technique to detect minute change in dielectrics at the given interface. The adsorbed layers of the organic materials were studied using a SPR instrument.

Current shot noise characteristics in biphenyl diamine and biphenyl dithiol devices

Current shot noise characteristics, away from their average current, in biphenyl diamine and biphenyl dithiol devices are investigated. The relations among the shot noise and the applied bias, the coupling factors, as well as the alligator clips are revealed. The regular change of the shot noise in biphenyl diamine device and irregular change of the shot noise in biphenyl dithiol device are shown as the coupling strength change from full coupling to weak coupling. It is found that the shot noise suppression in biphenyl diamine device is enhanced at the higher bias. The large differences of the shot noise suppression in the biphenyl dithiol device are revealed.

Patterning Gold Nanoparticle Using Scanning Electrochemical Microscopy

Patterned arrays of gold nanoparticles (AuNPs) are prepared using scanning electrochemical microscopy by electrochemical reduction of a gold salt at a platinum ultramicroelectrode positioned on top of an unbiased gold surface, modified with a biphenyl dithiol self-assembled monolayer (SAM). The synthesized AuNPs are chemisorbed on the thiolated SAM, and by moving the microelectrode in a lateral direction across the surface while applying a reduction potential, particle-like lines are generated.

Surface-Enhanced Raman Scattering and DFT Study of 4,4'-Biphenyldithiol on Silver Surface

Surfaced-enhanced Raman scattering (SERS) of 4,4'-biphenyldithiol (BPDT) has been investigated at a silver island film. Ordinary Raman (OR) spectra of neat sample in solid state and in basic solution have also been taken for comparison. The spectral feature in the SERS spectrum was similar to that for the OR spectrum in basic solution, except for the broadening of ring stretching bands indicative of the presence of surface-phenyl ring π interaction. In contrast, only absence of the C-H stretching band with very small Raman scattering crosssection seemed not pertinent in judging the definitive orientation of molecule. The observed vibrational bands in the SERS spectrum have been assigned by referring to the normal modes and wavenumbers from density functional theory (DFT) calculations of the simple model as 4,4'-biphenyldithiolates bound to two Ag atoms at the both ends. Excellent agreement between the experimental and the calculated results was achieved, which is remarkable considering the level of theory applied.

Conduction mechanisms in biphenyl dithiol single-molecule junctions

Based on density-functional theory calculations, we report a detailed study of the single-molecule charge-transport properties for a series of recently synthesized biphenyl-dithiol molecules [D. Vonlanthen et al., Angew. Chem., Int. Ed. 48, 8886 (2009); A. Mishchenko et al., Nano Lett. 10, 156 (2010)]. The torsion angle $\ensuremath{\phi}$ between the two phenyl rings, and hence the degree of $\ensuremath{\pi}$ conjugation, is controlled by alkyl chains and methyl side groups. We consider three different coordination geometries, namely, top-top, bridge-bridge, and hollow-hollow, with the terminal sulfur atoms bound to one, two, and three gold surface atoms, respectively. Our calculations show that different coordination geometries give rise to conductances that vary by one order of magnitude for the same molecule. Irrespective of the coordination geometries, the charge transport calculations predict a ${\mathrm{cos}}^{2}\ensuremath{\phi}$ dependence of the conductance, which is confirmed by our experimental measurements. We demonstrate that the calculated transmission through biphenyl dithiols is typically dominated by a single transmission eigenchannel formed from $\ensuremath{\pi}$ electrons. For perpendicular orientation of the rings a residual conductance arises from $\ensuremath{\sigma}$-$\ensuremath{\pi}$ couplings. But only for a single molecule with a completely broken conjugation we find a nearly perfect degeneracy of the $\ensuremath{\sigma}$-$\ensuremath{\pi}$ eigenchannels for the hollow-hollow-type contact in our theory.

Conventional Nanoindentation in Self‐Assembled Monolayers Deposited on Gold and Silver Substrates

Self‐assembled monolayers (SAMs) are promising materials for micromechanical applications. However, characterization of mechanical properties of monolayers is challenging for standard nanoindentation, and new efficient analysis techniques are needed. Hereby, a conventional nanoindentation method has been combined in a unique way with efficient data analysis based on consumed energy calculation and load‐displacement data. The procedure has been applied on SAMs of 4,4′‐biphenyldithiol (BPDT) on Au, 1‐tetradecanethiol (TDT), and 1‐hexadecanethiol (HDT) on Au and Ag substrates being the first study where SAMs of the same thiols on different substrates are analyzed by nanoindentation providing a new insight into the substrate effects. Unlike TDT and HDT SAMs, which are found to strongly enhance the homogeneity and stiffness of the underlying substrate, the BPDT covered Au substrate appears softer in mechanical response. In the case of TDT and HDT SAMs on Ag the structures are softer showing also faster relaxation than the corresponding structures on Au substrate. The proposed procedure enables a fast and efficient way of assessing the complex behaviour of SAM modified substrates. As a consequence, the results are relevant to practical issues dependent on layer activity and toughness.

In Situ Gap-Mode Raman Spectroscopy on Single-Crystal Au(100) Electrodes: Tuning the Torsion Angle of 4,4′-Biphenyldithiols by an Electrochemical Gate Field

In situ gap-mode Raman spectra were acquired in an electrochemical environment on a single-crystal gold electrode employing a Au(100)|4,4'-biphenyldithiol (BPDT)|Au-NP(55 nm) sandwich assembly. This geometry enabled an investigation of the influence of an applied electrochemical gate field on the conformational changes in nanojunctions, such as the torsion angle (φ) of molecules. A linear correlation between the intensity ratio I(C═C)/I(C(ring)-S) and cos(2) φ in 4,4'-BPDT-type molecular junctions was established and subsequently utilized to estimate the potential dependence of the torsion angle of the "flexible" molecule M1 at different potentials. The latter decreases as the potential (charge) becomes more negative, resulting in better π-π coupling, which correlates with enhanced junction conductance. The demonstrated spectroelectrochemical strategy and the direct correlation of the spectroscopic results with (single) molecular conductance studies may guide the selection and elucidation of functional molecules for potential applications in novel nanodevices.

Assessment of a nanoparticle bridge platform for molecular electronics measurements

A combination of electron beam lithography, photolithography and focused ionbeam milling was used to create a nanogap platform, which was bridged by goldnanoparticles in order to make electrical measurements and assess the platformunder ambient conditions. Non-functionalized electrodes were tested to determinethe intrinsic response of the platform and it was found that creating devices inambient conditions requires careful cleaning and awareness of the contributionscontaminants may make to measurements. The platform was then used to makemeasurements on octanethiol (OT) and biphenyldithiol (BPDT) molecules byfunctionalizing the nanoelectrodes with the molecules prior to bridging the nanogap withnanoparticles. Measurements on OT show that it is possible to make measurements onrelatively small numbers of molecules, but that a large variation in response canbe expected when one of the metal–molecule junctions is physisorbed, whichwas partially explained by attachment of OT molecules to different sites on thesurface of the Au electrode using a density functional theory calculation. Onthe other hand, when dealing with BPDT, high yields for device creation arevery difficult to achieve under ambient conditions. Significant hysteresis in theI–V curves of BPDT was also observed, which was attributed primarily to voltage inducedchanges at the interface between the molecule and the metal.