Behavior Of Organic Molecules Research Articles

Probing molecular architectures and interactions with scanning tunneling microscopy on graphite and arachidic acid functionalized surfaces

This study investigates the application of scanning tunneling microscopy in exploring molecular structures and interfaces relevant to nanotechnology. Graphite was selected as a sample due to its ease of visualization of atomic arrangements and surface inertness. The surface of highly oriented pyrolytic graphite treated with arachidic acid (C20H32O2) was examined to gain insights into the behavior of organic molecules at liquid-solid interfaces. Through detailed observations, the study demonstrates the versatility of scanning tunneling microscopy in elucidating molecular architectures and interactions. The findings underscore the importance of scanning tunneling microscopy in advancing our understanding of molecular systems and driving progress in nanotechnology applications. This work highlights the pivotal role of scanning tunneling microscopy in unraveling the complexities of nanoscale phenomena and fostering future innovations in the field.

Position and Orientation dependent Hybridization and Energy transfer of Dipole Emitter around Plasmonic Homodimers

AbstractA dipole emitter (analogous to organic molecules) placed near any dielectric or metal nanoparticles, based on their spatially constrained location and orientation, vividly emulate optical nanoantennas. Herein, we have extensively simulated the single dipole emitter interaction with spherical homodimers of noble metal gold and silver nanoparticles for different positional dependent orientations, exemplifying systematically the hybridization (Rabi splitting), quenching and diffuse non‐radiative energy transfer effects. The blue‐shifted scattering spectra of the coupled dipole emitter with individual Ag and Au homodimers quantify and corroborate the corresponding quantum yield/efficiency estimations. Such spatially oriented emitter interaction further distinctly reveals the enhanced near‐field and far‐field effects of the plasmonic dimer system in terms of dipolar and quadrupolar resonances, arising due to the induced polarization by respective incident electric and opto‐magnetic field components. Understanding the surface‐enhanced behavior of organic molecules that are either incorporated or randomly attached (experimentally) on the surface of metal nanoparticles will benefit greatly from the present comprehensive data analysis.

Dual ASE from the monomeric and excimeric states of a conjugated-polymer (PDHF) in solution

Abstract In this work, the spectral and amplified spontaneous emission (ASE) properties of a conjugated polymer poly [9, 9-di-(2′-ethylhexyl) fluorenyl-2, 7-diyl] (PDHF) in tetrahydrofuran (THF) have been studied. Our results showed that the absorption spectra of PDHF in THF have only one peak under wide range of concentrations (0.012 mol/m3 to 0.39 mol/m3), it could be seen that the shape of the absorption did not change; this indicates no dimer formation in these solutions for all concentrations mentioned above. On the other hand, the fluorescence spectra of PDHF in THF, at low concentration, showed two peaks, the primary at 415 nm and the secondary at 435 nm. The effects of concentration and the temperature on PDHF in THF under same conditions were studied. For example, the intensity of the peak at 435 nm became increasingly stronger for higher concentration and lower temperature. These are analogs to the excimeric behavior of organic molecules. Under high power pulsed laser excitation, we observed ASE at 418 nm and 437 nm. These ASE peaks could arise from the monomer and excimer states of the macromolecule respectively. The ASE spectra of PDHF were compared with the rhodamine 6 G (Rh 6 G). The most important and distinguishing features are that PDHF has a two times better photochemical stability than rhodamine 6 G and high optical gain compared with the conventional laser dyes.

A Progress in Gold Nanoparticles: Adsorption Behavior

This perspective reviews recent developments in the adsorption behavior and the adsorption kinetics of gold nanoparticles(AuNPs),with emphasis on papers initiating the developments and with an eye to their consequences. The aspect adsorption behavior of organic molecules on AuNPs have included the adsorption pattern of thionine, 1,4-PDI , 4-Methoxypyr-idine, 1,2,3-triazole and SH-PEG5K and the influence of adsorption. The aspect adsorption characteristics of biomolecules on AuNPs have included the adsorption kinetics of single-stranded DNA and proteins on the AuNPs. The last key aspect adsorption AuNPs on self-assembled monolayers have included the adsorption kinetics of AuNPs on different SAMs and semiconductor crystals.

Organic reactivity of alcohols in superheated aqueous salt solutions: an overview

The low dielectric constant and high self-dissociation constant of water in a temperature range between 150 and 250 °C make it a very appealing solvent for synthesis. Surprisingly, while organic chemistry in water at low temperature or around its critical point has been investigated in detail, very little seems to be known about the behaviour of organic molecules under hydrothermal conditions. The present work thus aims at shading some light on this field. As a start, we decided to investigate the reactions in which alcohols can undergo in water in the above-mentioned temperature range. Knowing that very strong salt effects on organic reactions have already been observed in super critical water, the impact of salt on the outcome of our tests was also investigated in detail.

Adsorption of organic molecules on the TiO2(011) surface: STM study

High resolution scanning tunneling microscopy has been applied to investigate adsorption and self-assembly of large organic molecules on the TiO(2)(011) surface. The (011) face of the rutile titania has been rarely examined in this context. With respect to possible industrial applications of rutile, quite often in a powder form, knowledge on behavior of organic molecules on that face is required. In the presented study we fill in the gap and report on experiments focused on the self-assembly of organic nanostructures on the TiO(2)(011) surface. We use three different kinds of organic molecules of potential interest in various applications, namely, PTCDA and CuPc representing flat, planar stacking species, and Violet Landers specially designed for new applications in molecular electronics. In order to reach a complete picture of molecular behavior, extended studies with different surface coverage ranging from single molecule up to 2 monolayer (ML) thick films are performed. Our results show that the adsorption behavior is significantly different from previously observed for widely used metallic templates. Creation of highly ordered molecular lines, quasi-ordered wetting layers, controlled geometrical reorientation upon thermal treatment, existence of specific adsorption geometries, and prospects for tip-induced molecule ordering and manipulation provide better understanding and add new phenomena to the knowledge on the (011) face of rutile titania.

Heat dissipation and non-equilibrium phonon distributions in molecular devices

Using a density functional approach we compute vibrations of molecules adsorbed on metal and semiconducting substrates and the electronphonon coupling of these modes. A non-equilibrium Green’s function approach is used to compute the partially coherent transmission in molecular junctions due to electron-vibration scattering [1], [2]. The electronic power dissipated into molecular vibrations allows to set a rate equation for the phonon population in the vibrational degrees of freedom of the molecule. The rate equation includes the phonon emission rate and phonon decay due to absorption, electron-hole pair production and dissipation into the contacting leads, which are assumed to behave as reservoirs. The rate of phonon decay is computed using a microscopic approach which includes a first-principle calculation of the coupling of the molecular modes with the vibrations of the contacts. In turn, the calculated phonon lifetime is used to correct the phonon propagator. As the power dissipated in the molecular junction depends nontrivially on the phonon populations, the equilibrium distribution under bias condition is a complex issue. A self consitent loop allows to compute the steady state non-equilibrium phonon population of the molecular junction under bias condition. We find that the resulting average population is far from the equilibrium thermal distribution, frequently assumed in such calculations, which allows to obtain a mean temperature of the junction. As expected the deviations increase with applied bias. As molecular electronics is moving to semiconducting substrates, it is relevant to explore and understand thermal issues. Metallic substrates have in fact a very efficient channel of phonon damping into electron-hole pairs, while vibrational coupling to the substrate may not be very efficient due to ionic mass mismatch and a weaker bond. On the other hand the the electron-hole generation is prevented on semiconducting substrates, where instead vibrational coupling is stronger.We compare thermal behavior of organic molecules adsorbed on Si with molecules adsorbed on metallic substrates (Au or Cu) and determine the molecular temperature as a function of applied bias and for different temperatures of the termostats.

Adsorption of n-Butanol from Aqueous Solutions on a Bi–Ga Electrode

Curves of the differential capacitance at the Bi–Ga/H2O interface in 0.05 M Na2SO4 solutions with different concentrations of n-C4H9OH are obtained by a bridge method at 420 Hz and 32°C. Adsorption parameters of n-C4H9OH, determined by a regression analysis of these curves, are compared with relevant data for mercury and partially fused polycrystalline bismuth (pBi). That the adsorption behavior of organic molecules at Hg differs from that at pBi and Bi–Ga is due not to their different hydrophilicity but to a different physical interaction water–electrode. The reason for this phenomenon can be an unequal spread of electron density beyond the ionic cores of Hg and Bi. These notions are corroborated by the fact that the Bi–Ga data fit overall correlation dependence between the “electronic” capacitance of different electrodes in the absence of a chemisorption interaction metal–water and the adsorbability of the n-C4H9OH molecules on them.

Behavior of unsaturated organic molecules in the nanospace of stage-2 cesium–graphite intercalation compounds

Intercalation reaction of benzene (C 6H 6) into CsC 24 and the characteristics of resulting ternary graphite intercalation compound (GIC) have been investigated, in comparison with the similar CsC 24–ternary GICs with ethylene (C 2H 4) and acrylonitrile (C 2H 3CN), and the behavior of these organic molecules within the interlayer nanospace has been discussed. The stability of these ternary GICs under exposure in air, in both stage structure and electrical conductivity was found to be in the order of C 2H 4–, C 6H 6– and C 2H 3CN–GICs. This result was reasonably explained as follows: the C 2H 4 molecules in the interlayer space oligomerize considerably and form network preventing diffusion of the Cs atoms in the interlayer, while the C 6H 6 molecules form only dimers or trimers and unable to form network, and the C 2H 3CN molecules, in spite of their strong tendency to polymerize, apparently do not form oligomers in the interlayer space, and its ternary GIC tends to degrade easily. By the electrical and galvanomagnetic measurements, it is revealed that the dominant carrier of these ternary GICs is electrons, even when the electrical conductivity decreases considerably after prolonged exposure in air, while the host graphite, Grafoil, shows two-carrier conduction. This fact indicates that the degradation of the ternary GICs occurs mainly at the periphery or surface layer of the crystallite, and at the inside of the crystallite, the ternary stage structure is retained unchanged.

有機分子の微視的挙動を用いた超薄膜デバイス

有機分子の微視的挙動を用いた超薄膜デバイス

Infrared Spectra and Vibrational Analysis of Phenyl Selenocyanates

Abstract Systematic studies on the vibrational behaviour of organic molecules are of considerable interest since a good knowledge of the intramolecular vibrations often helps to establish spectra-structure correlations. In continuation of previous investigations on different classes of organic compounds (1–3), a vibrational analysis concerning a group of phenyl selenocyanates has been undertaken here.

Synthetic Bilayer Membranes-Self-Assembling Behavior of Organic Molecules

The self-assembling behavior of synthetic amphiphiles is discussed. The bilayer membrane is formed spontaneously in water from a variety of dialkyl (C10-C20) amphiphiles with cationic, anionic, nonionic, and zwitterionic hydrophilic head groups. Appropriate triple-chain amphiphiles with rigid segments similarly produce the bilayer assembly. Two-headed, single-chain amphiphiles form the monolayer membrane. These results establish that the formation of molecular membranes is a general physicochemical phenomenon. The aggregate morphology (vesicle, lamella, tube, disk, etc) can be related to the molecular structure in the case of a group of the single-chain amphiphile. Physicochemical chracteristics (binding of biomolecules, phase transition and phase separation) of the synthetic bilayer are discussed.

Abstract: Orbital shifts associated with chemical bonding of organic molecules on ZnO nonpolar surfaces

Several recent experiments on transition‐metal surfaces have demonstrated the value of uv photoemission spectroscopy (UPS) for understanding the chemisorption of molecular adsorbates on solid surfaces.1 In these experiments adsorption‐induced changes in the binding energy of molecular orbitals from their free‐molecule values were observed. These shifts involve two effects of comparable size: (i) extramolecular relaxation/polarization shifts1–3 present for all orbitals and (ii) chemical bonding shifts of those orbitals directly involved in chemisorption bonding of the molecule to the surface. Since for all orbitals of a particular adsorbed molecule the relaxation/polarization shifts appeared to be essentially the same, the orbitals forming the chemical bond to the surface could be identified.1We have used UPS at hν=40.8 eV to observe the position of valence orbitals of a wide variety of organic molecules adsorbed on atomically clean ZnO (11̄00) nonpolar surfaces in ultrahigh vacuum at 120 and 300 K. ZnO is at the same time a metal oxide known to be catalytically active and also a wide‐gap tetrahedral semiconductor (wurtzite structure). Of particular interest is the behavior of organic molecules containing π and lone‐pair electron orbitals. These orbitals should be active in chemisorption bonding because they are energetically high lying (weakly bound) and because they protrude significantly from the molecule.A number of molecules (e.g., C2H4, H2, O2, CO) produce no significant changes in the ZnO UPS spectrum at either 300 or 120 K, except for small band‐bending changes which rigidly shift the entire spectrum in energy by ?0.1–0.3 eV. At 300 K, strong changes in the shape of the spectrum are found only for adsorbates which decompose on the surface (e.g., HCOOH4). At 120 K, many molecules adsorb to produce marked spectral changes in the UPS spectrum. Compared to their gas phase counterparts, the adsorbate orbitals appearing in the difference spectrum are in each case shifted upward (to smaller binding energies) by an increment ΔER which in many cases (e.g., CO2, C2H2) is essentially constant for all orbitals. In nearly all of the remaining cases, only the highest‐lying orbital(s) (at smallest binding energy) deviate from this pattern. We associate the upward shift of all orbitals with extramolecular relaxation/polarization effects. Since these shifts are uniform for most of the orbitals, as in the case of hydrocarbons on transition metals,1 similarly useful conclusions can be made from the UPS spectra of such semiconductor surfaces as ZnO about the nature of the chemisorption bond. With the assumption of a uniform relaxation/polarization shift for all orbitals, we then attribute the additional shift of high‐lying orbitals to chemical bonding to the surface via those orbitals. As in the case of Ni(111),1 benzene (C6H6) exhibits a dominant bonding shift (ΔEB?0.6 eV on ZnO) for the highest‐lying, doubly degenerate π orbital. We observe an additional bonding shift ΔEB?0.3 eV for two orbitals (σ and π) at larger binding energy. It is interesting to note that while both C2H4 and C2H2 chemisorb readily on Ni(111) with significant bonding shifts,1 C2H4 does not adsorb appreciably on ZnO(11̄00), and C2H2 displays only relaxation/polarization effects (without any additional chemical bonding shifts) and thus seems to be simply physisorbed.Ethylene oxide (C2H4O), methanol (CH3OH), and acetone [(CH3)2CO] display bonding shifts ΔEB?0.6, 0.4, and 0.7 eV, respectively, for their highest‐lying, oxygen lone‐pair orbitals. In dimethyl sulfoxide [(CH3)2SO] the highest‐lying orbital undergoes a bonding shift ΔEB?1.2 eV. One low‐lying orbital of (CH3)SO exhibits a shift on adsorption which is significantly different (∠1 eV) from the uniform relaxation/polarization shift of all other low‐lying orbitals. Adsorbed CO, produced by H2+CO coadsorption at 120 K or by formic acid (HCOOH) decomposition at 300 K, reveals bonding shifts ΔEB?1.0 and 0.6 eV for both its highest‐lying 5σ (carbon lone‐pair) and 1π orbitals, respectively.4 This multiple‐bonding behavior for CO may be a consequence of the open atomic structure and directed‐bond character of the partially covalent ZnO surface.

Vibrational Spectra of Methyl-Phenyl-Sulfoxides in the Range 700–50 cm−1

Abstract Investigations on the vibrational behaviour of organic molecules in the low infrared region are of considerable interest since they often provide helpful results for a better knowledge of the molecular parameters. Although the vibrational features of simple benzene derivatives have been extensively investigated in the past years (1–3), the spectral analysis of more complex and less symmetrical molecules still appears rather difficult, mainly because in such systems strong coupling effects may occur. In the previous paper of this series (4) a vibrational analysis on a number of acetophenones was presented. Results for a group of methyl-phenyl-sulfoxides also including some deuterated derivatives are reported in the present work. It may be pointed out that a number of differences in the spectra of the two classes of compounds was observed.