Dilute Solutions In Nonpolar Solvents Research Articles

Effect of Ethynyl Linkages on the Properties of the Derivatives of Triphenylamine and 1,8-Naphthalimide

Three new derivatives of triphenylamine containing different number of 1,8-naphthalimide moieties linked via ethynyl linkages were obtained by a Sonogashira cross-coupling reaction and their properties were studied. The glass-forming derivatives showed glass transition temperatures ranging from 73 to 96 °C. They showed high thermal stabilities with the temperatures of the onset of thermal degradation ranging from 421 to 462 °C. Fluorescence quantum yields of the dilute solutions in nonpolar solvents of the compounds ranged from 0.063 to 0.94 while those of the solid films were in the range of 0.011–0.25. Small singlet–triplet gap was predicted by DFT calculations, which was confirmed by the similarity between the prompt and the delayed fluorescence energies. Cyclic voltammetry measurements revealed close values of the solid state ionization potentials ranging from 5.48 to 5.61 eV and electron affinities ranging from −3.29 to −3.16 eV. The layer of 4,4′-((di(N-(2-ethylhexyl)-1,8-naphthalimide-4-yl)phenyl)e...

New derivatives of triphenylamine and naphthalimide as ambipolar organic semiconductors: Experimental and theoretical approach

Four new derivatives of triphenylamine containing different number of naphthalimide moieties were designed and synthesized by Suzuki condensation and their properties were studied by the experimental and theoretical tools. The compounds obtained are capable to form molecular glasses with glass transition temperatures ranging from 45 °C to 84 °C. They exhibit very high thermal stabilities with 5% weight loss temperatures ranging from 429 °C to 483 °C. Fluorescence quantum yields of the dilute solutions in nonpolar solvents of the synthesized materials range from 0.63 to 0.78. Due to the pronounced electron donor–acceptor character, the compounds show dramatic solvatochromic red shifts of fluorescence (up to 250 nm) in polar solvents. The ionization potentials of the solid samples of the compounds established by electron photoemission spectrometry in air ranged from 5.57 to 6.01 eV. 4-(4′-(Di-(4″-methoxyphenyl)amino)phenyl)-N-(2-ethylhexyl)-1,8-naphthalimide (5) was found to show ambipolar charge transport in air with the mobilities of charges exceeding 10−4 cm2 V−1 s−1 at high electric fields. The electron mobility of the compounds containing no methoxy groups were found to exceed the hole mobility by 2–3 orders of magnitude. The special role of methoxy groups in the ambipolar charge transport character of compound 5 is discussed in the frame of hopping Marcus theory, by applying a static theoretical analysis followed by a qualitative discussion of the positional disorder in some of these materials.

A comparative study of non-polar solvents effect on dielectric relaxation and dipole moment of binary mixtures of mono alkyl ethers of ethylene glycol and of diethylene glycol with ethyl alcohol

Dielectric relaxation and dipole moment of binary mixtures of homologous series of mono alkyl ethers of ethylene glycol and of diethylene glycol, i.e., mono methyl, mono ethyl and mono butyl ethers of ethylene glycol (ROCH 2CH 2OH) and mono methyl, mono ethyl and mono butyl ethers of diethylene glycol (ROCH 2CH 2OCH 2CH 2OH) with ethyl alcohol (C 2H 5OH) of different concentrations were studied in dilute solutions of benzene, dioxane and carbon tetrachloride at 35 °C. Permittivity ( ε′) and loss ( ε″) at 10.1 GHz, static dielectric constant ε o at 1 MHz and high frequency limiting dielectric constant ε ∞ = n D 2 at optical frequency of these molecules and their binary mixtures at different concentration were measured in dilute solutions of non-polar solvents. The average relaxation time τ o, relaxation times corresponding to overall molecular reorientation τ 1 and group rotations τ 2 were determined using Higasi's single frequency measurement equations for dilute solutions. The evaluated values of relaxation times and free energy of activation Δ F were used to explore the solvent effect on molecular dynamics of these polar binary systems in non-polar solvents. The excess inverse relaxation time and excess free energy of activation were determined to confirm the existence of hydrogen-bonded heterogeneous cooperative domains of the ethers and alcohol molecules at different concentration their binary mixtures in non-polar solvents. The dipole moment of the binary mixtures was evaluated using Higasi's and Guggenheim's equation for dilute solutions. The evaluated values of dipole moments and computed dipole moment values using a simple mixing equation of the polar molecules binary mixture were used to explore the effect of non-polar solvent environment on heterogeneous molecular interactions between ethers and alcohol molecules. The effect of number of carbon atoms in the molecular structure of these homologous series molecules was also considered for the interpretation of various evaluated dielectric parameters.

Dielectric properties of low molecular weight poly(ethylene glycol)s

This paper reports the measured values of dielectric permittivity e′ and dielectric loss e″ of ethylene glycol, diethylene glycol and poly(ethylene glycol)s of average molecular weight 200, 300, 400 and 600 g mol−1 in the pure liquid state. The measurements have been carried out in the frequency range 200 MHz to 20 GHz at four different temperatures of 25, 35, 45 and 55 °C. The complex plane plots (e″ versus e′) of these molecules are Cole–Cole arcs. The static dielectric constant e0, high-frequency limiting dielectric constant e∞, average relaxation time τ0 and distribution parameter α have been determined from these plots. The value of the Kirkwood correlation factor g and the dielectric rate free energy of activation ΔF have also been evaluated. The dependence of relaxation time on molecular size and viscosity has been discussed. A comparison has also been made with the dielectric behaviour of these molecules in dilute solutions of non-polar solvents, which were carried out earlier in this laboratory. The influences of intermolecular hydrogen bonding and molecular chain coiling on the dielectric relaxation of these molecules have been recognized. © 2000 Society of Chemical Industry

Evaluation of a 4 MHz integrated circuit oscillator for the measurement of solute dipole moments in dilute solution

A simple device for the measurement of solute dipole moments in dilute solutions of nonpolar solvents is described and evaluated. The device is based on an integrated circuit radio frequency oscillator and is demonstrated to be capable of measuring changes in solution dielectric constant of less than one part in 10 000. This allows the measurement of solute dipole moments using solutions in the 0.0001–0.005 molar range. Solute–solute interactions are shown to be minimized within this concentration range, and a simple means of extracting the solute dipole moment from concentration‐dependent dielectric constant measurements is described. Dipole moments of para‐(dimethylamino)benzonitrile, nitrobenzene, para‐(nitro)anisole, and para‐(nitro)aniline are measured, and are shown to compare favorably with previously reported values. The device is demonstrated to be capable of distinguishing solution dielectric constant changes associated with solute concentration changes as low as 3×10−5 M. It is therefore well suited to the measurement of dipole moments of polar compounds whose solubility in nonpolar solvent is low.

Computation of polarizability anisotropies for molecules in dilute solution: An approach to the local field correction

This study shows that calculated polarizability anisotropies for molecules in solution are highly dependent on the near-molecule local-field correction, which is neglected in the Lorentz continuum local-field approximation. A direct approach that relies on a knowledge of the solute molecular structure, the liquid structure of the solvent, and density functional theory (DFT) calculation techniques, is proposed to compute the local-field correction, and consequently the apparent polarizabilities for molecules in dilute solution in nonpolar solvents. Polarizability anisotropies for a group of organic molecules in solution in carbon tetrachloride are calculated, and the results compare favorably with experimental data.

Estimation of molecular anisotropy coefficients by a dielectric method

Using three butyl chloride isomers as test compounds, it is shown that the shape of polar molecules determines in a significant manner the dielectric properties of their dilute solutions in non-polar solvents. Taking into account the anisotropy of both the shape and the polarizability of molecules allows one to reach a useful correlation of the apparent dipole moments determined from solutions and the value obtained in the gaseous phase.

Thione–thiol tautomerism and stability of 2- and 4-mercaptopyridines and 2-mercaptopyrimidines

The possible thione–thiol tautomerism of 2- and 4-mercaptopyridines, 2-mercaptopyrimidine, and 4,6-dimethyl-2-mercaptopyrimidine in solution is studied by means of absorption (UV–VIS) spectroscopy. In accordance with earlier observations, polar solvents and self-association shift the apparent tautomeric equilibrium significantly towards the thione form. In dilute solutions of nonpolar solvents the thiol form predominates. On standing, significant changes are observed in the absorption spectra of these tautomeric compounds in ethanol, dioxane, and water. The time course of the tautomerization, followed spectrophotometrically, reveals quantitative transformation of the thiol form to the corresponding symmetrical disulfides. The influence of concentration, temperature, and irradiation with indirect sunlight are discussed. This thione–disulfide process is reversible in water, starting either from the tautomeric thione or from its symmetrical disulfide, implying a possible importance in biological systems. Keywords: thione–thiol tautomerism, absorption spectra, thiol–disulfide oxidation, mercaptopyridines and pyrimidines.

Electron trapping by methanol aggregates in dilute solution in nonpolar solvents

In order to further elucidate the mechanism of electron solvation in polar liquids we have determined the rate of electron attachment to solute methanol aggregates, as a function of methanol concentration, in two nonpolar solvents. An infrared technique was used to measure the extent of methanol aggregation in the solutions. The methanol is present as monomer at low concentration but at high concentration forms aggregates which are mostly pentamers. The electron in unreactive with monomer but reacts at high rate with aggregate species. The reaction with pentamers is reversible, but the electron reacts irreversibly with larger aggregates. The results indicate a dynamic nature for the electron which can autodetach from shallow traps.

Vibrational spectra and molecular structure of 2,2,3,3-tetrabromobutane

The i.r. and Raman spectra of MeBr 2CCBr 2Me, in the crystalline state, are reported. The i.r. spectra of the same substance in dilute solutions in nonpolar solvents have also been obtained. Taking the CBr stretching bands as a guide to qualitative understanding of the experimental results it is shown that point group C 2 h is a reasonable working approximation to the molecular symmetry. On this basis it has been possible to obtain nearly complete vibrational assignment for the molecule.

Die Abhängigkeit der Fluoreszenzquantenausbeute von der Anregungswellenlänge bei Carbonylverbindungen des Pyrens

Abstract Pyrene-3-aldehyde, 3-acetylpyrene and 3-benzoylpyrene show almost no fluorescence in dilute solution in non-polar solvents. In more concentrated solutions, however, a long wave fluorescence is observed, showing the existence of weak intermolecular forces, even in the ground state. In polar solvents, pyrene-3-aldehyde and 3-acetylpyrene exhibit short wave monomer fluorescence whilst 3-benzoylpyrene does not fluoresce. The intensity for both long and short wave fluorescence is dependent upon the excitation wave length and is a maximum for excitation in the weak long wave tail of the first absorption band. Molecules are thought to have a greater absorption in this region if they interact strongly with their polar or polarizable surroundings. Due to the very short singlet lifetime of isolated monomers (τ<C10-10 sec), such molecules have a greater probability of forming a fluorescence state than more weakly interacting ones.

Dielectric Relaxation and Molecular Structure. I. Dielectric Relaxation in Substituted Anilines

Abstract Measurements of static dielectric constant at 1 Mc, refractive index (for sodium D-line) and complex dielectric constant at 9.44 GHz (X-band) have been made to determine the relaxation times and dipole moments of N,N′-dimethylaniline (A), N,N′-diethylaniline (B), o-chloroaniline (C), m-chloroaniline (D) and p-chloroaniline (E) in dilute solutions of non-polar solvents. Substances A, B, C and D have been studied in n-heptane, benzene decalin and Nujol. The measurements for A and B have also been extended to cyclohexane, whereas E has only been studied in benzene. The values of relaxation time, calculated by Higasi’s equations in terms of a0, a′, a″ and a∞, and those of α, calculated from Cole-Cole’s equation in terms of the same parameters, showed an evidence for the existence of more than one relaxation mechanism. This has been interpreted in terms of the intramolecular rotations of the amino (or the substituted amino) group occurring simultaneously with the overall molecular orientation.

Trifluoroacetic acid. Nature of association in dilute solutions in nonpolar solvents

Trifluoroacetic acid. Nature of association in dilute solutions in nonpolar solvents

An infra-red study of the association of benzoic acid in the vapour phase, and in dilute solution in non-polar solvents

The infra-red spectra of benzoic acid in the vapour phase, and in dilute solution in cyclohexane, carbon tetrachloride, and benzene show two bands between 1770 and 1670 cm −1 which are assigned respectively to “free” carbonyl groups, and to carbonyl groups involved in hydrogen bonding between acid molecules. The intensities of these have been used to determine equilibrium constants for the dimerisation of benzoic acid in the vapour phase and in these solvents, in each case at several temperatures. The enthalpy and entropy changes of dimerisation have been evaluated; their magnitudes vary with the medium in the order: benzene < carbon tetrachloride < cyclohexane < vapour. The variations are attributed to decreasing interaction between the monomeric acid and the medium along this series.

Conformation and intramolecular hydrogen bonding in glucose and xylose derivatives

The nature of intramolecular hydrogen bonding in some O-methyl derivatives of glucose and xylose and related glycosides has been examined by means of IR studies of their hydroxyl stretching absorption measured in dilute solution in non-polar solvents. For most of the compounds studied the spectra are consistent with the predominance of the C1 conformation of the pyranose ring, but there is evidence of some departures from the ideal chair shape. The occurrence in 2,3-di-O-methyl- d-xylose of a lower frequency band near 3530 cm −1 suggests the presence of hydrogen bonds between cis meta diaxial groups, which would be possible only if the 1C conformer were present. The bands in the crystal spectra do not correspond to those in solution, showing that the weaker intramolecular hydrogen bonds are not favoured in the solid, where strong intermolecular bonds predominate.

Effect of Hydrogen Bonding on the Deformation Frequencies of the Hydroxyl Group in Alcohols

The effects of hydrogen bonding on the infrared spectra of aliphatic alcohols have been studied in the range 4000 to 350 cm—1. Twenty-six alcohols were investigated of which 10 were primary, 7 were branched primary, 6 were secondary, and 3 were tertiary. Attention was concentrated on the region of the spectrum between 1500 cm—1 and 350 cm—1 where the deformation vibrations of the OH group occur. Spectra were obtained of the alcohols (a) in dilute solution in nonpolar solvents, (b) in the liquid state, and (c) in the vapor state, the degree of association being followed by observation of the well-known effect of hydrogen bonding in the OH stretching vibration near 3.0μ. Methanol, ethanol, and hexanol-1 were also investigated after deuteration of the OH group. All the alcohols exhibited a broad diffuse association band with a maximum near 650 cm—1. This has been assigned to the out-of-plane deformation vibration of the H atom in the COH group. All the alcohols also exhibited a broad association band which usually had 2 maxima near 1410 cm—1 and 1330 cm—1. This band (which appears to have been missed by previous workers) is assigned to the in-plane deformation vibration of the H atom in the COH group. The corresponding monomeric band varies between 1200 cm—1 and 1330 cm—1 in undeuterated alcohols and between 870 cm—1 and 930 cm—1 in deuterated alcohols. There is in addition a very narrow association band which lies near 1100 cm—1 in primary and secondary alcohols and near 1165 cm—1 in tertiary alcohols. This is assigned to the effect of hydrogen bonding on the skeletal vibrations, which involve stretching of the CO bond. It appears that the effects of hydrogen bonding on the deformation motions of the OH group are quite complex and that steric effects, rotational isomerism, and interaction with C – H deformation frequencies may all be involved to some extent.

Electric Polarization of Carboxylic Acids in Dilute Solutions of Nonpolar Solvents I. The Relation of Electric Polarization to the Association of Carboxylic Acids in Hydrocarbon Solvents

The association and polar character of various carboxylic acids have been studied in the solvents benzene and heptane by means of measurements of the electric polarization in very dilute solutions. The data have been analyzed by assuming an equilibrium between dimers and monomers of the acid molecules. A rather large anomalous contribution to the polarization of the dimer has been found. Possible origins of this polarization have been briefly considered.

POLARIZATION MEASUREMENTS ON CARBOXYLIC ACIDS IN DILUTE SOLUTION IN NON‐POLAR SOLVENTS

The effective use of dielectric polarization measurements in investigating the association of polar molecules in non-polar solvents has been largely confined to a study of the association of alcohols. These show significant changes in their state of aggregation in a range of concentrations sufEiciently high so that the equipment and methods hitherto available for dielectric constant measurements in solutions can be successfully applied to the investigation of their extent of association. The case of the carboxylic acids in non-polar solvents is quite different. Freezing point determinations show that extremely low concentrations must be attained before significant changes in the state of aggregation occur. This range of concentrations in the case of many of the acids lies below 2 X mole fraction. As a consequence it has been difficult to make sufficiently accurate measurements by most of the methods for molecular weight determination in solution to yield quantitative information about the molecular state of these acids in dilute solution in non-polar solvents. While it has been possible to use the freezing point method, this is applicable only a t a single temperature and so gives information about temperature coefficients and energies of association only through the use of estimates made at other temperatures by other methods. In this paper a description will be given of some of the improvements which were made in apparatus and methods in order to carry out dielectric polarization measurements in very low concentrations in non-polar solvents under anhydrous conditions. In view of the low concentrations involved it is necessary to include a comprehensive statement of the errors of the method. A detailed discussion of the methods employed for interpreting and analyzing the results from the standpoint of the association of the solutes is aIso incIuded.