Synthesis of terphenyl oligomers as molecular electronic device candidates

Six functionalized bis(phenylene ethynylene)-p,p-terphenyls (BPETs) have been synthesized as potential molecular electronic devices. The molecules containing mono- and dinitro terphenyl cores, were rationally designed based on the electronic properties recently found in oligo(phenylene ethynylene)s (OPEs). From our understanding of the conductance properties in OPEs, improvement of electronic properties may be possible by using BPETs due to a higher rotational barrier between the central aromatic rings of the compounds prepared here. BPETs cores were functionalized with nitro groups and with different metallic adhesion moieties (alligator clips) to provide new compounds for testing in the nanopore and planar testbed structures.     

Synthesis of thiol substituted oligoanilines for molecular device candidates

The synthesis of thioacetate derivatized oligoanilines designed for molecular electronic device purposes is described. Reversible oxidation between the non-conductive leuco base and conductive emeraldine salt forms of these compounds may produce switching effects and device behavior. The targeted compounds contain a sulfur moiety as a means to connect the molecules to metallic electrodes.     

Synthesis and testing of new end-functionalized oligomers for molecular electronics

Several new classes of oligomers have been synthesized with functionalities designed to aid in the understanding of molecular device behavior, specifically when molecules are interfaced between proximal electronic probes. The compounds synthesized are series of azobenzenes, bipyridines and oligo(phenylene vinylene)s that bear acetyl-protected thiols for ultimate attachment to metallic surfaces. Some initial electrochemical and solid-state test results are also reported.     

Physically based molecular device model in a transient circuit simulator

Two efficient, physically based models for the real-time simulation of molecular device characteristics of single molecules are developed. These models assume that through-molecule tunnelling creates a steady-state Lorentzian distribution of excess electron density on the molecule and provides for smooth transitions for the electronic degrees of freedom between the tunnelling, molecular-excitation, and charge-hopping transport regimes. They are implemented in the fREEDA™ transient circuit simulator to allow for the full integration of nanoscopic molecular devices in standard packages that simulate entire devices including CMOS circuitry. Methods are presented to estimate the parameters used in the models via either direct experimental measurement or density-functional calculations. The models require 6–8 orders of magnitude less computer time than do full a priori simulations of the properties of molecular components. Consequently, molecular components can be efficiently implemented in circuit simulators. The molecular-component models are tested by comparison with experimental results reported for 1,4-benzenedithiol.     

Synthesis and characterization of new heptacyclic helicenes

New helically chiral substituted heptacyclic systems have been prepared from a simple phenanthrene building block in good yields and purity, via a four-step sequence involving palladium-catalysed Heck coupling and oxidative photocyclization. X-ray crystal structure analysis indicated that the conformation resembled that of the unsubstituted heptahelicene. The optical properties of these heptacyclic helicenes were investigated and show interesting behaviour.     

I/V characteristics of a molecular switch

We present a study of the conduction properties of a class of aromatic compounds, whose conformation can be modulated with a transverse electric field, with strong effects on the molecular transport properties. The theoretical method includes the molecule–electrode interaction in a simple, although effective way: the coupling matrix elements are considered independent from the energy of the continuum spectrum of the lead. This results in a simple expression for the molecular Green’s function with a significant simplification in the expression of the transmission function. The effects of the voltage bias on the electronic molecular density is included through a uniform effective electric field. A simplified but accurate method for the evaluation of the molecular response to the field, which spares lengthy computations for each value of the voltage, is presented. The proposed method is calibrated on the widely studied benzene-1,4-dithiol molecule. The calculations on the selected molecular wire (a tetracyano derivative of 4,4′-di(mercaptoethynyl)tolan) show that conductivity is low for perpendicular rings, whereas conduction is allowed for the planar conformation, which corresponds to the equilibrium geometry in the absence of the transverse electric field.     

Synthesis,molecular structure and reactivity of new biferrocenylpropane derivatives

New biferrocenylpropane derivatives FcC(CH₃)₂Fc′-C≡C–R [Fc?=?C₅H₅FeC₅H₄; Fc′?=?C₅H₅FeC₅H₃, R?=?C₆H₅ (L ₁ ), Fc (L ₂ )] and their complexes [FcC(CH₃)₂Fc′-C≡C–R][Co₂(CO)₆] [R?=?C₆H₅ (1); R?=?Fc (2)] have been synthesized by the Castro-Stephens coupling reaction and the reactions of ligands L ₁ , L ₂ with Co₂(CO)₈. Compounds L ₁ , L ₂ , 1 and 2 were characterized by elemental analysis, IR, ¹H (¹³C) NMR and MS, and the molecular structures of ligands L ₁ , L ₂ were determined by X-ray single crystal analysis. The electrochemical properties of L ₁ , L ₂ , 1 and 2 demonstrate two or three resolved one-electron redox processes.     

Synthesis and greener pastures biological study of bis-thiadiazoles as potential Covid-19 drug candidates

A novel series of bis- (Abdelhamid et al., 2017, Banerjee et al., 2018, Bharanidharan et al., 2022)thiadiazoles was synthesized from the reaction of precursor dimethyl 2,2′-(1,2-diphenylethane-1,2-diylidene)-bis(hydrazine-1-carbodithioate) and hydrazonyl chlorides in ethanol under ultrasonic irradiation. Spectral tools (IR. NMR, MS, elemental analyses, molecular dynamic simulation, DFT and LUMO and HOMO) were used to elucidate the structure of the isolated products. Molecular docking for the precursor, 3 and ligands 6a-i to two COVID-19 important proteins M^pro and RdRp was compared with two approved drugs, Remdesivir and Ivermectin. The binding affinity varied between the ligands and the drugs. The highest recorded binding affinity of 6c with M^pro was (?9.2 kcal/mol), followed by 6b and 6a, (?8.9 and ?8.5 kcal/mol), respectively. The lowest recorded binding affinity was (?7.0 kcal/mol) for 6 g. In comparison, the approved drugs showed binding affinity (?7.4 and ?7.7 kcal/mol), for Remdesivir and Ivermectin, respectively, which are within the range of the binding affinity of our ligands. The binding affinity of the approved drug Ivermectin against RdRp recoded the highest (?8.6 kcal/mol), followed by 6a, 6 h, and 6i are the same have (?8.2 kcal/mol). The lowest reading was found for compound 3 ligand (?6.3 kcal/mol). On the other side, the amino acids also differed between the compounds studied in this project for both the viral proteins. The ligand 6a forms three H-bonds with Thr 319(A), Sr 255(A) and Arg 457(A), whereas Ivermectin forms three H-bonds with His 41(A), Gly143(A) and Gln 18(A) for viral M^pro. The RdRp amino acids residues could be divided into four groups based on the amino acids that interact with hydrogen or hydrophobic interactions. The first group contained 6d, 6b, 6 g, and Remdesivir with 1–4 hydrogen bonds and hydrophobic interactions 1 to 10. Group 2 is 6a and 6f exhibited 1 and 3 hydrogen bonds and 15 and 14 hydrophobic interactions. Group 3 has 6e and Ivermectin shows 4 and 3 hydrogen bonds, respectively and 11 hydrophobic interactions for both compounds. The last group contains ligands 3, 6c, 6 h, and 6i gave 1–3 hydrogen bonds and 6c and 3 recorded the highest number of hydrophobic interactions, 14 for both 6c and 6 h. Pro Tox-II estimated compounds’ activities as Hepatoxic, Carcinogenic and Mutagenic, revealing that 6f-h were inactive in all five similar to that found with Remdesivir and Ivermectin. The drug-likeness prediction was carried out by studying physicochemical properties, lipophilicity, size, polarity, insolubility, unsaturation, and flexibility. Generally, some properties of the ligands were comparable to that of the standards used in this study, Remdesivir and Ivermectin.     

Facile synthesis of high molecular weight aromatic polyformals containing phthalazinone moiety

High molecular weight aromatic polyformals containing phthalazinone moiety were simply synthesized with a high‐intensity mixing methodology without the presence of phase‐transfer catalyst. Aromatic polyformals can readily be afforded in a very short time and at temperatures ranging from 50 to 140 °C. These polyformals showed high glass‐transition temperatures together with superior thermal properties when compared with a 4,4′‐isopropylidenediphenol (BPA)‐type polyformal and polycarbonate. The glass‐transition temperatures of these aromatic polyformals ranged from 94 to 229 °C. The molecular weights of the polyformals were examined by gel permeation chromatographic technology, and the result showed that the cyclic formation during the condensation could be dramatically reduced at elevated temperature. The molecular weights and solubility increased with an increasing content of bisphenol A in the polyformals. The result demonstrated that the aromatic polyformal with 50% phthalazinone moiety showed the comparable thermal properties with commercial BPA polycarbonate. This method promisingly opened an effective approach to synthesize aromatic polyformals with high molecular weight and without cyclic formations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1441–1448, 2002     

Synthesis and evaluation of new lipomonosaccharide-imprinted polymers as MISPE supports

Molecular imprinted polymers (MIP) were prepared by the copolymerization of styrene (S) or methyl methacrylate (MMA) and methacrylic acid (MAA) using ethylene glycol dimethacrylate (EGDMA) as the crosslinker with molar ratios of [monomer]/[crosslinker] and [MAA]/[template] of 3:7 (to obtain a rigid structure) and 1:6 (to optimise hydrogen interactions), respectively. The polymerizations occurred in presence of the template molecule (MIP) - GlcNcouma - an amphiphilic monosaccharide. The same materials, non-imprinted polymers (NIP), were also prepared in absence of the template. These MIPs were characterized and used as SPE supports for selective enrichment. The results showed the correlation between retention efficiency and the porogen character of the polymerization solvent.     

Models of charge transport and transfer in molecular switch tunnel junctions of bistable catenanes and rotaxanes

The processes by which charge transfer can occur play a foundational role in molecular electronics. Here we consider simplified models of the transfer processes that could be present in bistable molecular switch tunnel junction (MSTJ) devices during one complete cycle of the device from its low- to high- and back to low-conductance state. The bistable molecular switches, which are composed of a monolayer of either switchable catenanes or rotaxanes, exist in either a ground-state co-conformation or a metastable one in which the conduction properties of the two co-conformations, when measured at small biases (+0.1 V), are significantly different irrespective of whether transport is dominated by tunneling or hopping. The voltage-driven generation (±2 V) of molecule-based redox states, which are sufficiently long-lived to allow the relative mechanical movements necessary to switch between the two co-conformations, rely upon unequal charge transfer rates on to and/or off of the molecules. Surface-enhanced Raman spectroscopy has been used to image the ground state of the bistable rotaxane in MSTJ-like devices. Consideration of these models provide new ways of looking at molecular electronic devices that rely, not only on nanoscale charge-transport, but also upon the bustling world of molecular motion in mechanically interlocked bistable molecules.     

Single-chain and monolayered conjugated polymers for molecular electronics

Exploring the charge transport properties and electronic functions of molecules is of primary interest in the area of molecular electronics. Conjugated polymers (CPs) represent an attractive class of molecular candidates, benefiting from their outstanding optoelectronic properties. However, they have been less studied compared with the small-molecule family, mainly due to the difficulties in incorporating CPs into molecular junctions. In this review, we present a summary on how to fabricate CP-based singlechain and monolayered junctions, then discuss the transport behaviors of CPs in different junction architectures and finally introduce the potential applications of CPs in molecular-scale electronic devices. Although the research on CP-based molecular electronics is still at the initial stage, it is widely accepted that (1) CP chains are able to mediate long-range charge transport if their molecular electronic structures are properly designed, which makes them potential molecular wires, and (2) the intrinsic optoelectronic properties of CPs and the possibility of incorporating desirable functionalities by synthetic strategies imply the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.     

Synthesis of covalently bonded nanostructure from two porphyrin molecular wires leading to a molecular tube

Molecular wire, diacetylene-linked porphyrin dimer 6 having terminal alkenes, was synthesized. Porphyrin dimer 6 formed the 1:1 double-stranded ladder complex with 1,4-diazabicyclo[2.2.2]octane (DABCO). The co-planar stacked two porphyrin molecular wires in the ladder complex were connected by olefin metathesis in the presence of the Grubbs catalyst in order to make a covalently bonded tubular nanostructure. The obtained molecular tube 7 was characterized by ¹H, ¹³C NMR spectroscopy, and MALDI-TOF MS spectrometry.     

Synthesis of optically active amphiphilic tetrathiafulvalene derivatives

The synthesis and characterization of novel chiral tetrathiafulvalenes bearing two long alkyl chains at one end of the π-electron rich unit and different functional groups—ester, acid or thiolate—at the other extreme is described. The synthetic method requires the preparation of 1,3-dithiol derivatives with two stereogenic centers. Different routes and reaction conditions were explored to form these compounds, whose optimized synthesis involved the nucleophilic substitution of a chiral bromo methylene derivative with tetrabutylammonium bis(2-thioxo-1,3-dithiole-4,5-dithiolate)zincate. The tetrathiafulvalenes were prepared by coupling the 1,3-dithiol derivative with 4,5-bis(methoxycarbonyl)-1,3-dithiol-2-one or 4,5-bis(2-cyanotehylthio)-1,3-dithiol-2-thione. The products were fully characterized, including by circular dichroism spectroscopy, which confirmed their optical activity. They are promising candidates to be used as building blocks in supramolecular materials for molecular electronics, to produce systems with unique electrical, magnetic or optical properties that stem from their chirality.     

H-bonding template-directed synthesis of a complete m-PDA-bridged ladder polyhydrosiloxane （OLPHS）

A highly ordered m-phenylenediimino-bridged ladder polyhydrosiloxane (abbr. OLPHS) with Mn = 1.24 104 was synthesized under assistance of H-bonding template constructed from imino H-bonding, N(Si)-H N(Si)-H, via a modified process of stoichiometric hydrolysis and dehydrochlorination condensation reaction between Si–Cl and Si–OH bonds. The complete ladder structure of OLPHS has been confirmed by the following three data. Two characteristic Bragg’s peaks representing the ladder width (w =0:94 nm) and ladder thickness (t = 0.42 nm) were observed in XRD analysis, which are consistent with those cal- culated by molecular simulation. The very sharp absorption with a small half-peak width ew1=2=0:5 ppmT for [(–HN)HSiO2/2]n moiety of OLPHS in 29Si NMR spectrum indicated presence of the complete ladder structure. As collateral evidence, a higher glass transition temperature (Tg = 105 8C) is also recorded in the DSC measurement, implying the high stiffness of ladder chain of OLPHS.     

Synthesis,anticancer activity,and molecular docking of new pyrazolo[1,5-a]pyrimidine derivatives

The reaction of 3-aminopyrzoles with dimethylamino-acrylonitrile derivatives was utilized for the production of new functionalized pyrazolopyrimidine compounds 4a-c and 6a-c. The structures of the obtained pyrazolopyrimidines were characterized by the different spectroscopic measurements (IR, NMR, and mass analyses). The DFT quantum chemical calculations were applied to the determination of the HOMO-LUMO energies and Mulliken atomic charges. The investigated derivatives exhibited a low HOMO-LUMO energy gap, ranging from 2.70 to 2.34 eV, 4c and both 4b and 6b, respectively. Furthermore, the anticancer activities of the synthesized compounds have also been investigated against four cancer cells as well as normal cells (WI38). The investigated compounds demonstrated an impressive cytotoxic effect on MCF-7 and Hep-2 cells. On comparison with 5-fluorouracil, pyrazolopyrimidines 6a–c showed promising cytotoxic action against MCF-7 and Hep-2, with IC₅₀ values of 18.31–26.51 and 24.15–27.16 μM, respectively. Molecular docking of the prepared pyrazolopyrimidines 4 and 6 with the crystal structure of the KDM5A protein, obtained from the PDB, revealed the types of the protein's binding sites.     

Improved and new syntheses of potential molecular electronics devices

New syntheses of ethyl and nitro substituted oligo(phenylene ethynylene)s (OPEs) have been developed. To further explore whether the presence of nitro functionality in OPEs leads to switching and memory capabilities, new nitro substituted OPEs have been designed and synthesized. An isatogen-based system, a structure that is isomeric to the nitro OPE, has been synthesized. Additionally, pyridine-based and chromium-based compounds have been synthesized. We surmise that redox reactions of these candidates may impart switching capabilities and electrochemical studies are shown. U-shaped OPEs were synthesized to inhibit leakage of metals deposited during formation of top contacts on self-assembled monolayers (SAMs). The OPEs contain either thiol-based moieties or isonitrile groups to enable formation of SAMs on metal substrates.     

Synthesis of phenanthrimidazole from 9,10-phenanthraquinone and aldehydes by molecular iodine as catalyst

A new, convenient, efficient, and cost-effective one-pot synthesis of 1H-phenanthro[9,10]imidazol-2-yl from phenantheren-quinone and aldehydes, using molecular iodine as catalyst is described. The present methodology offers several advantages such as excellent yields, simple procedure, shorter reaction times, and the use of inexpensive reagents.     

Diamine anchored molecular junctions of oligo(phenylene ethynylene) cruciform

Using diamine as anchoring group, the self-assembled monolayers (SAMs) based on oligo(phenylene ethynylene)s (OPEs) and cruciform OPEs with an extended tetrathiafulvalene (TTF) (OPE3 and OPE3-TTF) were successfully formed on the Au substrate and then utilized in molecular junctions by conductingprobe atomic force microscopy (CP-AFM).     

In situ measurements of oligoaniline conductance: Linking electrochemistry and molecular electronics

The single-molecule conductance of a dithiolated aniline trimer has been measured under potential control and also under an inert solvent. In each experiment, two sets of currents are found, differing by a factor 4, and these are tentatively assigned to differing connections to the electrodes (e.g., on-top vs. hollow sites). The conductances peak (to 17 ± 1.6 and 5.8 ± 0.85 nS) between the first and second oxidations of the molecule and change smoothly with surface potential. There is no evidence for a coexistence of oxidized and reduced molecules. Measurements made at a fixed surface potential as a function of tip to substrate bias show a peak current at 0.1 V followed by a region of negative differential resistance. This is accounted for semi-quantitatively by modification of the local potential by the applied bias altering the oxidation state of the molecule under the probe. Measurements made in toluene are Ohmic, indicating that the tip does not alter the oxidation state of the molecule in the absence of screening ions. We discuss the role of gap geometry and bonding in these processes.