Terphenyl Molecules Research Articles

Assembling Surface Molecular Sierpiński Triangle Fractals via K+-Invoked Electrostatic Interaction.

Molecular Sierpiński triangles (STs), a family of elegant and well-known fractals, can be prepared on surfaces with atomic precision. Up to date, several kinds of intermolecular interactions such as hydrogen bond, halogen bond, coordination, and even covalent bond have been employed to construct molecular STs on metal surfaces. Herein a series of defect-free molecular STs have been fabricated via electrostatic attraction between potassium cations and electronically polarized chlorine atoms in 4,4″-dichloro-1,1':3',1″-terphenyl (DCTP) molecules on Cu(111) and Ag(111). The electrostatic interaction is confirmed both experimentally by scanning tunneling microscopy and theoretically by density functional theory calculations. These findings illustrate that electrostatic interaction can serve as an efficient driving force to construct molecular fractals, which enriches our toolbox for the bottom-up fabrication of complex functional supramolecular nanostructures.

Infrared ellipsometry study of the charge dynamics in K3p -terphenyl

We report an infrared ellipsometry study of the charge carrier dynamics in polycrystalline ${\mathrm{K}}_{x}p$-terphenyl samples with nominal $x=3$, for which signatures of high-temperature superconductivity were previously reported. The infrared spectra are dominated by two Lorentzian bands with maxima around 4000 and $12 000 {\mathrm{cm}}^{\ensuremath{-}1}$ which, from a comparison with calculations based on a H\"uckel model, are assigned to intramolecular excitations of $\ensuremath{\pi}$ electrons of the anionic $p$-terphenyl molecules. The intermolecular electronic excitations are much weaker and give rise to a Drude peak and a similarly weak Lorentzian band around $220 {\mathrm{cm}}^{\ensuremath{-}1}$. A dc resistivity of about $0.3 \mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$ at $300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is deduced from the IR data, comparable to values measured by electrical resistivity on a twin sample. The analysis of the temperature dependence of the low-frequency response reveals a gradual decrease of the plasma frequency and the scattering rate of the Drude peak below $300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ that gets anomalously enhanced below $90\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The corresponding missing spectral weight of the Drude peak appears blueshifted towards the Lorentz band at $220 {\mathrm{cm}}^{\ensuremath{-}1}$. This characteristic blueshift signifies an enhanced localization of the charge carriers at low temperatures and contrasts the behavior expected for a bulk superconducting state for which the missing spectral weight would be redshifted to a delta function at zero frequency that accounts for the loss-free response of the superconducting condensate. Our data might still be compatible with a filamentary superconducting state with a volume fraction well below the percolation limit for which the spatial confinement of the condensate can result in a plasmonic resonance at finite frequency.

Structure transformation from Sierpiński triangles to chains assisted by gas molecules.

Reversible transformations between fractals and periodic structures are of fundamental importance for understanding the formation mechanism of fractals. Currently, it is still a challenge to controllably achieve such a transformation. We investigate the effect of CO and CO2 molecules on Sierpiński triangles (STs) assembled from Fe atoms and 4,4″-dicyano-1,1':3',1″-terphenyl (C3PC) molecules on Au surfaces. Using scanning tunneling microscopy, we discover that the gas molecules induce a transition from STs into 1D chains. Based on density functional theory modeling, we propose that the atomistic mechanism involves the transformation of a stable 3-fold coordination Fe(C3PC)3 motif to Fe(C3PC)4 with an axially bonded CO molecule. CO2 causes the structural transformation through a molecular catassembly process.

Solvent Polarity Effect on The Electronic Spectra of Laser Dye (P- Terphenyl Molecule )

تهدف هذه الدراسة إلى التعرف على تأثير المذيبات المختلفة القطبية على الاطياف الإلكترونية ( الامتصاص و الفلورة) لصبغة بي- تيرفينيل في درجة حرارة الغرفة وبتركيزين 10-4M, 10-5M. وقد تم تقدير عزوم ثنائي القطب للحالتين المتهيجة الاولى والارضية من معادلات Lippert و Bakshiev -Kawski و Chamma- Viallet باستخدام تغاير ازاحة ستوك جنبا إلى جنب مع ثابت العزل للمذيب (Ɛ) ومعاملات الانكسار (n) .وقد لوحظ ان عزوم ثنائي القطب للحالات المتهيجة هي اكبر من تلك التي للحالات الارضية وهذا يشير الى حدوث اعادة توزيع كثافة الشحنة الالكترونية في الحالة المتهيجة الاكثر قطبية. ان التغاير التجريبي لقيم عزوم ثنائي القطب يمكن ان يفسر بصيغة التراكيب الرنينية الممكنة (اي حالة الحلقات الثلاث لجزيئة بي- تيرفينيل اي كونها في مستوى واحد او متعامدة ) ايضا.

Luminescence of Aromatic Compounds During Ultrasonic Treatment of Tb2(SO4)3 Suspension in Commercial Gasoline.

The spectral-luminescent properties of a suspension of terbium sulfate in commercial gasoline under sonication are studied. The following emitters are identified from the luminescence spectrum: *Tb3+ ions in crystals, electronically excited molecules of arenes (benzene, toluene, and xylenes), and polycyclic aromatic hydrocarbons (PAHs) in the liquid phase of the suspension. The study of sonotriboluminescence in gasoline-heptane and heptane-xylene-PAH synthetic mixtures shows for the first time that there is an effective luminescence activator in gasoline, that is, terphenyl molecules. It has been established that these molecules have the highest luminescence yield among all sonotriboluminescence emitters found. This is provided by the transfer of the excitation energy from monocyclic arene molecules primarily excited during the sonication. In this case, the primary excitation of aromatic hydrocarbon molecules in commercial gasoline during the ultrasonic treatment of suspensions occurs under the impact of charged particles/electrons generated during electrical discharges initiated by collision and destruction of microcrystals. This process is similar to radioluminescence excitation in liquid scintillators which can be considered commercial gasoline. The formation of *Tb3+ is due to separation and recombination processes of charges that populate the excited states of luminescence centers in microcrystals electrified during tribodestruction under sonication of the suspension.

Biphenylene carbon sheets

Nanomaterials Although graphene forms two-dimensional carbon sheets, other arrangements of carbon rings could also assemble as flat sheers. Fan et al. synthesized an ultraflat biphenylene carbon sheet consisting of sp2-hybridized carbon atoms forming four-, six-, and eight-membered rings on a gold surface. An adsorbed halogenated terphenyl molecule undergoes a two-step interpolymer dehydrofluorination polymerization that creates the four- and eight-membered rings through carbon–carbon bond formation. Scanning tunneling spectroscopy revealed that this carbon allotrope is metallic. Science , abg4509, this issue p. [852][1] [1]: /lookup/doi/10.1126/science.abg4509

Biphenylene network: A nonbenzenoid carbon allotrope.

The quest for planar sp2-hybridized carbon allotropes other than graphene, such as graphenylene and biphenylene networks, has stimulated substantial research efforts because of the materials' predicted mechanical, electronic, and transport properties. However, their syntheses remain challenging given the lack of reliable protocols for generating nonhexagonal rings during the in-plane tiling of carbon atoms. We report the bottom-up growth of an ultraflat biphenylene network with periodically arranged four-, six-, and eight-membered rings of sp2-hybridized carbon atoms through an on-surface interpolymer dehydrofluorination (HF-zipping) reaction. The characterization of this biphenylene network by scanning probe methods reveals that it is metallic rather than a dielectric. We expect the interpolymer HF-zipping method to complement the toolbox for the synthesis of other nonbenzenoid carbon allotropes.

Atomically Precise Engineering of Single‐Molecule Stereoelectronic Effect

AbstractCharge transport in a single‐molecule junction is extraordinarily sensitive to both the internal electronic structure of a molecule and its microscopic environment. Two distinct conductance states of a prototype terphenyl molecule are observed, which correspond to the bistability of outer phenyl rings at each end. An azobenzene unit is intentionally introduced through atomically precise side‐functionalization at the central ring of the terphenyl, which is reversibly isomerized between trans and cis forms by either electric or optical stimuli. Both experiment and theory demonstrate that the azobenzene side‐group delicately modulates charge transport in the backbone via a single‐molecule stereoelectronic effect. We reveal that the dihedral angle between the central and outer phenyl ring, as well as the corresponding rotation barrier, is subtly controlled by isomerization, while the behaviors of the phenyl ring away from the azobenzene are hardly affected. This tunability offers a new route to precisely engineer multiconfigurational single‐molecule memories, switches, and sensors.

Atomically Precise Engineering of Single-Molecule Stereoelectronic Effect.

Charge transport in a single-molecule junction is extraordinarily sensitive to both the internal electronic structure of a molecule and its microscopic environment. Two distinct conductance states of a prototype terphenyl molecule are observed, which correspond to the bistability of outer phenyl rings at each end. An azobenzene unit is intentionally introduced through atomically precise side-functionalization at the central ring of the terphenyl, which is reversibly isomerized between trans and cis forms by either electric or optical stimuli. Both experiment and theory demonstrate that the azobenzene side-group delicately modulates charge transport in the backbone via a single-molecule stereoelectronic effect. We reveal that the dihedral angle between the central and outer phenyl ring, as well as the corresponding rotation barrier, is subtly controlled by isomerization, while the behaviors of the phenyl ring away from the azobenzene are hardly affected. This tunability offers a new route to precisely engineer multiconfigurational single-molecule memories, switches, and sensors.

Effect of Anchoring Groups on the Conduction Properties of Terphenyl Molecules Connected to Copper Leads

We report equilibrium and non-equilibrium conductance of terphenyl molecules with different anchoring groups including sulfur and nitrogen atom. The corresponding molecules are terphenyl-dithiols (TPDT) and diamino-terphenyl (DATP). The non-equilibrium Green's function (NEGF) technique has been implemented on the density functional tight-binding (DFTB) code to perform computations of the electronic transport properties of molecular devices. The NEGFs are used to compute the electronic density self-consistently with open boundary condition naturally encountered in transport problem which is imposed by the potentials at the contacts. As result, the value of the molecular conductance with amine groups is higher about ten times than the thiol anchored group.

Diverse supramolecular structures self-assembled by a simple aryl chloride on Ag(111) and Cu(111).

Diverse self-assembled structures were obtained on Cu(111) and Ag(111) surfaces by using a simple and small 4,4''-dichloro-1,1':4',1''-terphenyl molecule. Surprisingly, a complicated supramolecular self-assembled vortex structure, composed of 15 molecules in a large unit, was realized through the collaboration of hydrogen bonding and halogen bonding.

One-Dimensionally Disordered Chiral Sorting by Racemic Tiling in a Surface-Confined Supramolecular Assembly of Achiral Tectons.

The aggregation of (pro)chiral/achiral molecules into crystalline structures at interfaces forms conglomerates, racemates, and solid solutions, comparable to known bulk phases. Scanning tunneling microscopy and Monte Carlo simulations were employed to uncover a distinct racemic phase, expressing 1D disordered chiral sorting through random tiling in surface-confined supramolecularly assembled achiral 4,4''-diethynyl-1,1':4',1''-terphenyl molecules. The configurational entropy of the 1D disordered racemic tiling phase was verified by analytical modeling, and found to lie between that of a perfectly ordered 2D racemate and a racemic solid solution.

One‐Dimensionally Disordered Chiral Sorting by Racemic Tiling in a Surface‐Confined Supramolecular Assembly of Achiral Tectons

AbstractThe aggregation of (pro)chiral/achiral molecules into crystalline structures at interfaces forms conglomerates, racemates, and solid solutions, comparable to known bulk phases. Scanning tunneling microscopy and Monte Carlo simulations were employed to uncover a distinct racemic phase, expressing 1D disordered chiral sorting through random tiling in surface‐confined supramolecularly assembled achiral 4,4′′‐diethynyl‐1,1′:4′,1′′‐terphenyl molecules. The configurational entropy of the 1D disordered racemic tiling phase was verified by analytical modeling, and found to lie between that of a perfectly ordered 2D racemate and a racemic solid solution.

Steering On‐Surface Reactions by a Self‐Assembly Approach

Abstract4,4′‐Bis(2,6‐difluoropyridin‐4‐yl)‐1,1′:4′,1′′‐terphenyl (BDFPTP) molecules underwent dehydrocyclization and covalent coupling reactions on Au(111) according to scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations. Self‐assembly of the reactants in well‐defined molecular domains prior to reaction could greatly enhance the regioselectivity of the dehydrocyclization reaction and suppress defluorinated coupling, demonstrating that self‐assembly can efficiently steer on‐surface reactions. Such a strategy could be of great importance in surface chemistry and widely applied to control on‐surface reactions.

Steering On-Surface Reactions by a Self-Assembly Approach.

4,4'-Bis(2,6-difluoropyridin-4-yl)-1,1':4',1''-terphenyl (BDFPTP) molecules underwent dehydrocyclization and covalent coupling reactions on Au(111) according to scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations. Self-assembly of the reactants in well-defined molecular domains prior to reaction could greatly enhance the regioselectivity of the dehydrocyclization reaction and suppress defluorinated coupling, demonstrating that self-assembly can efficiently steer on-surface reactions. Such a strategy could be of great importance in surface chemistry and widely applied to control on-surface reactions.

Construction of Sierpiński triangles with the coexistence of C60 or MnPc molecules.

Sierpiński triangles up to the fourth order were successfully prepared using 4,4''-dicyano-1,1':3',1''-terphenyl molecules and Fe or Co atoms with the coexistence of the third molecules (C60 or MnPc) on a reconstructed Au(111) substrate. Sierpiński triangles could be disturbed and restored by C60 molecules after annealing at 400 and 360 K, respectively. The dispersed MnPc molecules did not affect the formation of Sierpiński triangles when annealed at high temperatures. The selective adsorption of MnPc molecules at certain holes of Sierpiński triangles was observed.

Controlling Molecular Growth between Fractals and Crystals on Surfaces.

Recent studies demonstrate that simple functional molecules, which usually form two-dimensional (2D) crystal structures when adsorbed on solid substrates, are also able to self-assemble into ordered openwork fractal aggregates. To direct and control the growth of such fractal supramolecules, it is necessary to explore the conditions under which both fractal and crystalline patterns develop and coexist. In this contribution, we study the coexistence of Sierpiński triangle (ST) fractals and 2D molecular crystals that were formed by 4,4″-dihydroxy-1,1':3',1″-terphenyl molecules on Au(111) in ultrahigh vacuum. Growth competition between the STs and 2D crystals was realized by tuning substrate and molecular surface coverage and changing the functional groups of the molecular building block. Density functional theory calculations and Monte Carlo simulations are used to characterize the process. Both experimental and theoretical results demonstrate the possibility of steering the surface self-assembly to generate fractal and nonfractal structures made up of the same molecular building block.

Sierpiński-triangle fractal crystals with the C3v point group

Self-similar fractals are of importance in both science and engineering. Metal-organic Sierpiński triangles are particularly attractive for applications in gas separation, catalysis and sensing. Such fractals are constructed in this study by using 120° V-shaped 4,4″-dicyano-1,1′:3′,1″-terphenyl molecules and Fe atoms on Au(1 1 1), and studied in detail by low-temperature scanning tunneling microscopy. Density functional theory calculations are employed to rationalize the invisible Fe atoms in STM images. Monte Carlo simulations are performed to understand the formation mechanism of the surface-supported fractal crystals.

Effects of end groups on the rectifying performance in molecular devices

Based on the density-functional theory and the non-equilibrium Greens function method, a theoretical study of the electron transport for the systems consisting of the terphenyl molecule connected to two Au electrodes through end-group S (Se) is carried out. The results show that these systems have good rectifying performance and the maximum rectification ratio may reach approximately 6 at a bias of 2.8 V. The rectifying behavior is reduced significantly when one of the two S(Se) atoms located at right end of the molecule is replaced by H. The asymmetric coupling between the molecule and the metal interface leads to different spatial distributions of the MPSH and different shifts of molecular orbital energy levels under positive and negative biases, which is the mechanism of rectifying performance. The systems with S end-groups have obvious rectifying performance because the interaction between S and Au electrode is stronger than that between Se and Au electrode.

Electrode metal dependence of the rectifying performance for molecular devices: A density functional study

Carrying out theoretical calculations using the nonequilibrium Green’s function method combined with the density functional theory, the transport properties of the terphenyl molecule connected to the two Y (Y=Li, Al, or Au) metal electrodes are investigated. The results show that the electrode metals have a distinct influence on rectifying performance of such devices. For the Au electrode system, we can observe a best rectifying performance, next for the Al electrode system, and the rectifying effect can be nearly neglected for the Li electrode system. Our findings suggest that the rectifying characteristics are intimately related to electrode materials.