Naphthalene Molecules Research Articles

Ion–polycyclic aromatic hydrocarbon collisions: kinetic energy releases for specific fragmentation channels

We report on 30 keV He2 + collisions with naphthalene (C10H8) molecules, which leads to very extensive fragmentation. To unravel such complex fragmentation patterns, we designed and constructed an experimental setup, which allows for the determination of the full momentum vector by measuring charged collision products in coincidence in a recoil ion momentum spectrometer type of detection scheme. The determination of fragment kinetic energies is found to be considerably more accurate than for the case of mere coincidence time-of-flight spectrometers. In fission reactions involving two cationic fragments, typically kinetic energy releases of 2–3 eV are observed. The results are interpreted by means of density functional theory calculations of the reverse barriers. It is concluded that naphthalene fragmentation by collisions with keV ions clearly is much more violent than the corresponding photofragmentation with energetic photons. The ion-induced naphthalene fragmentation provides a feedstock of various small hydrocarbonic species of different charge states and kinetic energy, which could influence several molecule formation processes in the cold interstellar medium and facilitates growth of small hydrocarbon species on pre-existing polycyclic aromatic hydrocarbons.

A simple route to derivatives of benzo[j]fluoranthene

3,6,8,11-Tetramethoxybenzo[j]fluoranthene can be made from 1,6-dimethoxynaphthalene in a one-pot ferric chloride oxidation/methanol reduction procedure. The reaction is tolerant of the presence of substituents in the 7-position of the naphthalene nucleus and provides a quick and easy route to these particular benzo[j]fluoranthenes. The reactions presumably proceed through initial formation of a bond between the 4-positions of two naphthalene molecules followed by closure of the five-membered ring. Indeed in one case some 4,4′-binaphthyl was isolated from the reaction mixture and it was generally found that better yields of the benzo[j]fluoranthrenes were obtained starting from the 4,4′-binaphthyl rather than by using the naphthalene as the starting material. In an analogous manner to the ring-closure of the 4,4′-binaphthyls, starting from a hexakisalkoxyphenylnaphthalene, a hexakisalkoxyfluoranthene could be obtained.

Naphthalene dimer and naphthalene dimer with Ar: calibration calculations and the effect of Ar on the stability and vibrational frequencies

The harmonic vibrational frequencies of naphthalene and its dimers are computed using density functional theory including an empirical correction for dispersion. The C–H out-of-plane bending modes in the naphthalene dimers show a red or a blue shift depending on the relative orientation of the two naphthalene molecules. The addition of Ar atoms does not significantly affect the vibrational frequencies, but changes the energy separation between the two dimer conformations.

Solubilization of polycyclic aromatic hydrocarbons in C16E7 nonionic surfactant solutions

Polycyclic aromatic hydrocarbons (PAHs), namely, naphthalene, phenanthrene, and pyrene, were solubilized in nonionic surfactant micelles formed from heptaoxyethylene monohexadecyl ether (C16E7). The sizes of the PAH-incorporated micelles, and the location of the solubilized molecules, were studied using dynamic light scattering, transmission electron microscopy (TEM), and 1H nuclear magnetic resonance (NMR) spectroscopy. The solubilization of the PAHs increased significantly above a C16E7 concentration of 1mM, which corresponded to the point at which the morphology of the micelles changed from globular to string-like, as demonstrated by TEM imaging. The string-like micelles then grew with increasing incorporation of PAHs (naphthalene, phenanthrene, and pyrene). The 1H NMR chemical shifts of the discrete groups of the C16E7 micelles shifted upfield with increasing naphthalene concentration as a result of the ring current and/or local anisotropic effects of the PAH. The 1H peak of the oxyethylene segment at 3.7ppm clearly split with increasing naphthalene concentration in the C16E7 solution. The rotating frame nuclear Overhauser and exchange spectroscopy of naphthalene solubilized in C16E7 micelles showed a cross peak between the oxyethylene segment and the 1H naphthalene peaks. The NMR spectral measurements showed that the solubilized naphthalene molecules were located in the palisade region of the micelles rather than in the core.

Synthesis and Electronic Structure of Dissymmetrical, Naphthalene-Bridged Sandwich Complexes [Cp′Fe(μ-C10H8)MCp*]x (x = 0, +1; M = Fe, Ru; Cp′ = η5-C5H2-1,2,4-tBu3; Cp* = η5-C5Me5)

The dissymmetrical naphthalene-bridged complexes [Cp′Fe(μ-C10H8)FeCp*] (3; Cp* = η5-C5Me5, Cp′ = η5-C5H2-1,2,4-tBu3) and [Cp′Fe(μ-C10H8)RuCp*] (4) were synthesized via a one-pot procedure from FeCl2(thf)1.5, Cp′K, KC10H8, and [Cp*FeCl(tmeda)] (tmeda = N,N,N′,N′-tetramethylethylenediamine) or [Cp*RuCl]4, respectively. The symmetrically substituted iron ruthenium complex [Cp*Fe(μ-C10H8)RuCp*] (5) bearing two Cp* ligands was prepared as a reference compound. Compounds 3–5 are diamagnetic and display similar molecular structures, where the metal atoms are coordinated to opposite sides of the bridging naphthalene molecule. Cyclic voltammetry and UV/vis spectroelectrochemistry studies revealed that neutral 3–5 can be oxidized to monocations 3+–5+ and dications 32+–52+. The chemical oxidation of 3 and 4 with [Cp2Fe]PF6 afforded the paramagnetic hexafluorophosphate salts [Cp′Fe(μ-C10H8)FeCp*]PF6 ([3]PF6) and [Cp′Fe(μ-C10H8)RuCp*]PF6 ([4]PF6), which were characterized by various spectroscopic techniques, including EPR and 57Fe Mössbauer spectroscopy. The molecular structure of [4]PF6 was determined by X-ray crystallography. DFT calculations support the structural and spectroscopic data and determine the compositions of frontier molecular orbitals in the investigated complexes. The effects of substituting Cp* with Cp′ and Fe with Ru on the electronic structures and the structural and spectroscopic properties are analyzed.

Preparation of Novel Isotropic Pitch with High Softening Point and Solvent Solubility for Pitch-based Electrospun Carbon Nanofiber

The novel isotropic pitch that exhibits both high solvent solubility (100% soluble in THF) and a high softening point (over 200°C) was successfully synthesized by the bromination of 2-methylnaphthalene followed by dehydrobromination/polymerization and extraction in n-hexane to eliminate lighter constituents. The molecular structure of the pitch was relatively linear with flexible methylene cross-linkages between naphthalene molecules. During bromination, a reaction temperature of 180°C was necessary to induce bromine substitution of methyl hydrogen. Methylene cross-linkages were formed after the dehydrobromination reaction. The obtained pitch is a suitable precursor for electrospinning and meltspinning to prepare carbon nanofibers and carbon fibers, respectively.

An electron transmission spectrometer with a trochoidal electron monochromator

The design of an electron transmission spectrometer is described and test measurement results for naphthalene, 1,3-dichlorobenzene, and phenylacetylene molecules are given. The trochoidal electron monochromator allows one to reach a 30-meV resolution at a half-height volt-ampere characteristic.

Solution processed naphthalene diimide derivative as electron transport layers for enhanced brightness and efficient polymer light emitting diodes

Increasing the efficiency and lifetime of polymer light emitting diodes (PLEDs) requires a balanced injection and flow of charges through the device, driving demand for cheap and effective electron transport/hole blocking layers. Some materials, such as conjugated polyelectrolytes, have been identified as potential candidates but the production of these materials requires complex, and hence costly, synthesis routes. We have utilized a soluble small molecule naphthalene diimide derivative (DC18) as a novel electron transport/hole blocking layer in common PLED architectures, and compared its electronic properties to those of the electron transport/hole blocking small molecule bathocuproine (BCP). PLEDs incorporating DC18 as the electron transport layer reduce turn on voltage by 25%; increase brightness over three and a half times; and provide a full five-fold enhancement in efficiencies compared to reference devices. While DC18 has similar properties to the effective conjugated polyelectrolytes used as electron transport layers, it is simpler to synthesise, reducing cost while retaining favourable electron transport properties, and producing a greater degree of efficiency enhancement. The impact on device lifetime is hypothesized to be significant as well, due to the air-stability seen in many naphthalene diimide derivatives.

Melting of Naphthalene Confined in Mesoporous Silica MCM-41

The 2H nuclear magnetic resonance (NMR) solid-echo spectra of naphthalene molecules as guests in the mesopores of neat MCM-41 with a pore width of 3.3 nm were measured in the temperature regime from 180 to 250 K. A strong reduction of the melting point of the naphthalene molecules by 152 K is observed. The line shape changes in the melting region were simulated with two different models, namely, the model of a narrow distribution of activation energies, which is typical for a crystal-like phase, and a two-phase model. Both models indicate a relatively narrow distribution of melting points of the naphthalene molecules inside the pores, indicative of a rather well-defined structure of the naphthalene molecules inside the pores. This finding supports the proposal of a plastic crystalline phase previously proposed by other groups.

Molecular-Frame 3D Photoelectron Momentum Distributions by Tomographic Reconstruction

Naphthalene molecules are fixed in space by a laser field and rotated, in 2° steps, over 180°. For each orientation, they are ionized by an intense, circularly polarized femtosecond laser pulse, and the 2D projection of the photoelectron momentum distribution is recorded. The molecular-frame 3D momentum distribution is obtained by tomographic reconstruction from all 90 projections. It reveals an anisotropic electron distribution, angularly shifted in the polarization plane, that is not accessible by the 2D momentum images. Our theoretical analysis shows that the magnitude of the angular shift is very sensitive to the exact form of the laser-modified molecular potential.

Solvent effect on absorption and fluorescence of 1-1` binaphtalene aromatic molecule

The absorption and fluorescence spectra of 1-1` Binaphthalene (1-1` BN) molecule have been studied at different solution states in polar and non polar solvents at room temperature. It is noticed that the absorption spectrum of this molecule is similar to that of Naphthalene molecule at this temperature. The fluorescence spectrum of 1-1`BN molecule differs from that of the Naphthalene molecule. It is also found that a peak shifted towards shorter wavelength in the fluorescence spectrum when the solvent is changed. This is due to the polarity of the polar solvent. Key words: Absorption spectra, fluorescence spectra, aromatic molecule, Solvent effect.

Ice Growth from Supercooled Aqueous Solutions of Benzene, Naphthalene, and Phenanthrene

Classical molecular dynamics (MD) were performed to investigate the growth of ice from supercooled aqueous solutions of benzene, naphthalene, or phenanthrene. The main objective of this study is to explore the fate of those aromatic molecules after freezing of the supercooled aqueous solutions, i.e., if these molecules become trapped inside the ice lattice or if they are displaced to the QLL or to the interface with air. Ice growth from supercooled aqueous solutions of benzene, naphthalene, or phenanthrene result in the formation of quasi-liquid layers (QLLs) at the air/ice interface that are thicker than those observed when pure supercooled water freezes. Naphthalene and phenanthrene molecules in the supercooled aqueous solutions are displaced to the air/ice interface during the freezing process at both 270 and 260 K; no incorporation of these aromatics into the ice lattice is observed throughout the freezing process. Similar trends were observed during freezing of supercooled aqueous solutions of benzene at 270 K. In contrast, a fraction of the benzene molecules become trapped inside the ice lattice during the freezing process at 260 K, with the rest of the benzene molecules being displaced to the air/ice interface. These results suggest that the size of the aromatic molecule in the supercooled aqueous solution is an important parameter in determining whether these molecules become trapped inside the ice crystals. Finally, we also report potential of mean force (PMF) calculations aimed at studying the adsorption of gas-phase benzene and phenanthrene on atmospheric air/ice interfaces. Our PMF calculations indicate the presence of deep free energy minima for both benzene and phenanthrene at the air/ice interface, with these molecules adopting a flat orientation at the air/ice interface.

Temperature dependent excimer luminescence of naphthalenes on α-alumina

When ethyl, methoxy and methyl substituted naphthalenes are vacuum deposited on a dielectric surface and optically pumped, the luminescence that is observed is excimer fluorescence, because the morphology of the adlayer is amorphous. As the surface is heated, the thermal energy states that are available to the molecules become more broadly populated. Distinct disorder-to-order transition is observed by the onset of two characteristic spectral features, the decrease in the excimer intensity and the concomitant increase in the trap fluorescence. Since the position of the substitution in the naphthalene molecule affects the extent to which ordering occurs, the choice of adsorbates reflects the range of ordering that was observed. By depositing another adlayer of molecules that does not emit and desorbs at a lower temperature than the fluorophores, the surface dynamics was monitored by the luminescent changes as the molecules mixed at temperatures below desorption. Molecular fluorescence was observed in the bilayers that indicated the formation of clusters as the percolation occurred.

Theoretical Prediction of Triplet–Triplet Energy Transfer Rates in a Benzophenone–Fluorene–Naphthalene System

Triplet–triplet energy transfer in benzophenone–fluorene and benzophenone–fluorene–naphthalene molecules is theoretically investigated by using the rate theories and electronic structure calculations established for electron transfer. From the calculated electronic couplings for the single-step tunneling and multistep hopping pathways of the energy transfer from the donor benzophenone to the acceptor naphthalene, it is found that the tunneling comes from the direct electronic couplings between the donor and acceptor states, other than the coupling via the virtual bridge state in the conventional superexchange mechanism. The mode-specific reorganization energy calculations reveal that only the several high-frequency modes dominate the energy transfer, leading to an important nuclear tunneling effect. Succeedingly, with use of the obtained parameters, Fermi’s golden rule predicts the consistent energy transfer rates with experimental ones.

Identification of naphthalene carboxylase as a prototype for the anaerobic activation of non‐substituted aromatic hydrocarbons

Polycyclic aromatic hydrocarbons such as naphthalene are recalcitrant environmental pollutants that are only slowly metabolized by bacteria under anoxic conditions. Based on metabolite analyses of culture supernatants, carboxylation or methylation of naphthalene have been proposed as initial enzymatic activation reactions in the pathway. However, the extremely slow growth of anaerobic naphthalene degraders with doubling times of weeks and the little biomass obtained from such cultures hindered the biochemical elucidation of the initial activation reaction, so far. Here, we provide biochemical evidence that anaerobic naphthalene degradation is initiated via carboxylation. Crude cell extracts of the sulfate-reducing enrichment culture N47 converted naphthalene and (13)C-labelled bicarbonate to 2-[carboxyl-(13)C]naphthoic acid at a rate of 0.12 nmol min(-1) mg protein(-1) . The enzyme, namely naphthalene carboxylase, catalysed a much faster exchange of (13) C-labelled bicarbonate with the carboxyl group of 2-[carboxyl-(12)C]naphthoic acid at a rate of 3.2 nmol min(-1) mg protein(-1), indicating that the rate limiting step of the carboxylation reaction is the activation of the naphthalene molecule rather than the carboxylation itself. Neither the carboxylation nor the exchange reaction activities necessitate the presence of ATP or divalent metal ions and they were not inhibited by avidin or EDTA. The new carboxylation reaction is unprecedented in biochemistry and opens the door to understand the anaerobic degradation of polycyclic aromatic hydrocarbons which are among the most hazardous environmental contaminants.

First-principles study of naphthalene-based single-electron transistor

We have performed first-principle calculations based on density functional theory (DFT) and non-equilibrium greens functions (NEGF) for calculating the charging energies of molecular system weakly coupled to an environment. We apply this approach to the molecule naphthalene, which is lying flat on gate dielectric between the source and drain electrodes. Our calculated values of charging energy for naphthalene in an isolated case are in good agreement with experimental values. Further, in an electrostatic environment, the result shows renormalization of molecular energy levels and therefore reduces the charging energy of naphthalene. Subsequently, the charge stability diagram of naphthalene based single-electron transistor (SET) has been obtained by calculating the charging energies as a function of an external gate potential. This diagram shows the dependence of SET conductance on the gate voltage and the source-drain bias. Our implementation is intended to predict the charging energies of the naphthalene-based SETs that reveals further scope in realization of the devices at nanoscale.

Electronic Spectra of Gas-Phase Polycyclic Aromatic Nitrogen Heterocycle Cations: Isoquinoline+and Quinoline+

Electronic spectra of the gas-phase isoquinoline(+)-Ar and quinoline(+)-Ar complexes are recorded using photodissociation spectroscopy by monitoring the Ar loss channel. The D(3)←D(0) and D(4)←D(0) band origins for isoquinoline(+)-Ar are observed at 15245 ± 15 cm(-1) and 21960 ± 15 cm(-1), respectively, whereas for quinoline(+)-Ar they appear at 16050 ± 15 cm(-1) and 21955 ± 15 cm(-1), respectively. Strong vibronic progressions for the D(3)←D(0) band systems of both isoquinoline(+)-Ar and quinoline(+)-Ar are modeled and assigned in terms of ring deformation and carbon-carbon stretch vibrational modes using time-dependent density functional theory calculations in conjunction with Franck-Condon simulations. The properties of the isoquinoline(+) and quinoline(+) molecules are compared with those of the isoelectronic naphthalene(+) molecule. The existence of strong progressions in the visible spectra of isoquinoline(+)-Ar and quinoline(+)-Ar suggests that the corresponding isoquinoline(+) and quinoline(+) molecular cations are unlikely to be responsible for diffuse interstellar bands.

A nanomechanical mass sensor with yoctogram resolution

Nanomechanical resonators have been used to weigh cells, biomolecules and gas molecules, and to study basic phenomena in surface science, such as phase transitions and diffusion. These experiments all rely on the ability of nanomechanical mass sensors to resolve small masses. Here, we report mass sensing experiments with a resolution of 1.7yg (1yg=10(-24)g), which corresponds to the mass of one proton. The resonator is a carbon nanotube of length ∼150nm that vibrates at a frequency of almost 2GHz. This unprecedented level of sensitivity allows us to detect adsorption events of naphthalene molecules (C(10)H(8)), and to measure the binding energy of a xenon atom on the nanotube surface. These ultrasensitive nanotube resonators could have applications in mass spectrometry, magnetometry and surface science.

Adsorption of Naphthalene and Ozone on Atmospheric Air/Ice Interfaces Coated with Surfactants: A Molecular Simulation Study

The adsorption of gas-phase naphthalene and ozone molecules onto air/ice interfaces coated with different surfactant species (1-octanol, 1-hexadecanol, or 1-octanal) was investigated using classical molecular dynamics (MD) simulations. Naphthalene and ozone exhibit a strong preference to be adsorbed at the surfactant-coated air/ice interfaces, as opposed to either being dissolved into the bulk of the quasi-liquid layer (QLL) or being incorporated into the ice crystals. The QLL becomes thinner when the air/ice interface is coated with surfactant molecules. The adsorption of both naphthalene and ozone onto surfactant-coated air/ice interfaces is enhanced when compared to bare air/ice interface. Both naphthalene and ozone tend to stay dissolved in the surfactant layer and close to the QLL, rather than adsorbing on top of the surfactant molecules and close to the air region of our systems. Surfactants prefer to orient at a tilted angle with respect to the air/ice interface; the angular distribution and the most preferred angle vary depending on the hydrophilic end group, the length of the hydrophobic tail, and the surfactant concentration at the air/ice interface. Naphthalene prefers to have a flat orientation on the surfactant coated air/ice interface, except at high concentrations of 1-hexadecanol at the air/ice interface; the angular distribution of naphthalene depends on the specific surfactant and its concentration at the air/ice interface. The dynamics of naphthalene molecules at the surfactant-coated air/ice interface slow down as compared to those observed at bare air/ice interfaces. The presence of surfactants does not seem to affect the self-association of naphthalene molecules at the air/ice interface, at least for the specific surfactants and the range of concentrations considered in this study.

Vibrational spectra of polyatomic molecules assisted by quantum thermal baths

We assess the performance of colored-noise thermostats to generate quantum mechanical initial conditions for molecular dynamics simulations, in the context of infrared spectra of large polyatomic molecules. Comparison with centroid molecular dynamics simulations taken as reference shows that the method is accurate in predicting line shifts and band widths in the ionic cluster (NaCl)(32) and in the naphthalene molecule. As illustrated on much larger polycyclic aromatic hydrocarbons, the method also allows fundamental spectra to be evaluated in the limit of T = 0, taking into account anharmonicities and vibrational delocalization.