Spectroscopic study on charge transfer molecular complexes of pyrazole derivatives with some pi-electron acceptors

Charge transfer molecular complexes of some pyrazole donors (pyrazole, 4-methylpyrazole, 3-methylpyrazole and 3,5-dimethylpyrazole) with 2,3-dichloro-5,6-dicyano-1,4-p-benzoquinone and tetracyanoethylene as pi-electron acceptors have been studied in CH2Cl2 at 25 degrees C. Spectral characteristics and stability constants of the formed charge transfer (CT) complexes are discussed in terms of the nature of donor and acceptor molecular structure, as well as in relation to solvent polarity. Thermodynamic parameters (deltaH, deltaG and deltaS) associated with CT complex formation are also examined. It was concluded that the formed CT complexes are of n-pi type with 1:1 (D:A) composition.     

Charge transfer complex studies between some non-steroidal anti-inflammatory drugs and pi-electron acceptors

Charge transfer (CT) complexes of some non-steroidal anti-inflammatory drugs, naproxen and etodolac which are electron donors with some pi-acceptors, such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), p-chloranil (p-CHL), have been investigated spectrophotometrically in chloroform at 21 degrees C. The coloured products are measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptors. Beer's law is obeyed and colours were produced in non-aqueous media. All complexes were stable at least 2 h except for etodolac with DDQ stable for 5 min. The equilibrium constants of the CT complexes were determined by the Benesi-Hildebrand equation. The thermodynamic parameters DeltaH, DeltaS, DeltaG degrees were calculated by Van't Hoff equation. Stochiometries of the complexes formed between donors and acceptors were defined by the Job's method of the continuous variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands in all cases.     

Sulfur-containing vinyl monomers. XII. Charge transfer complexes of thioethylene derivatives with π-electron acceptors

The absorption spectra of charge-transfer (CT) complexes of thioethylene derivatives with p-chloranil (CA), tetracyanoethylene (TCNE), and 7,7,8,8,-tetracyanoquinodimethane (TCNQ) were measured in methylene chloride. Since the CT bands of alkyl vinyl sulfides having bulky substituents such as isopropyl, cyclohexyl and tert-butyl were similar to that of methyl vinyl sulfide, the complexing site of these sulfides to acceptor was assumed to be the vinyl group rather than the sulfur atom. In the case of the TCNE complex of phenyl vinyl sulfide, however, a new second CT band at 378 nm was observed, and the first CT band was also close to that of ethyl phenyl sulfide, indicating that the TCNE formed a complex with this vinyl sulfide mainly at its phenyl group. To investigate further the conformation of the complex, CT spectra of bis-, tris- and tetrakis (phenylthio) ethylenes were measured. These compounds showed markedly different CT bands, and the changes in these CT bands with the number of the phenylthio substituents appears to be attributable to the change in complexing site with the acceptors used.     

Charge transfer complexes of some N-methylated thiohydantoins with molecular iodine

Using a series of N-methylated thiohydantoins as substrates, the donor properties of the sulfur atom are measured by determining the stability constants (K) of their adducts with molecular iodine. The K's have been determined by recording the UV-visible spectra of several CH₂Cl₂ solutions with different amounts of the reagents. The experimental data fit the 1:1 adduct model for all the compounds. The K values, compared with those previously found for the unsubstituted hydantoins and with those obtained for 5-methyl-2-thiohydantoin, show that the hydrogen-bonding interaction between the NH hydrogen and the S-bonded iodine plays an important role in determining the stability of the adduct. The K values obtained for several pentaatomic rings, all containing the thioureido group  HN C() NH , are discussed on the basis of the influence of the substituents at C-4 and C-5 on the donor properties of the sulfur atom.     

Charge transfer complexes of 9-vinyl-carbazole with pi acceptors in homogeneous and in micellar solutions

The molecular association of 9-vinyl-carbazole (CBZ) with three electron acceptors, p-chloranil (CHL), 2,7-dinitro-9-fluorenone (FL), and tetracyano-p-quinodimethane (TCNQ), is studied in acetonitrile and in micellar aqueous solution of sodium dodecyl sulfate (SDS). In both media, stable charge transfer (CT) complexes are formed with association constants in the range of 8-500 M(-1). CBZ and FL form a 1:2 complex in acetonitrile, but in SDS micelles the association is 1:1 due to size restriction and occupancy statistics in the host aggregates. The combination of absorption and fluorescence emission spectroscopy data indicates that the bimolecular CT complex of CBZ with TCNQ is stabilized in two distinct environments of the SDS micelles providing then two separated CT absorption bands.     

Charge transfer complexes of fullerene C60 with N,N-dimethylaniline derivatives

Charge transfer complexes of a series of p-substituted dimethylanilines with C₆₀ fullerenes were studied by electron absorption spectroscopy. Energies of charge transfer bonds depend on three effects of substituents in the donor molecule (the inductive, resonance, and polarization effects) with domineering of the resonance effect. The energies are linearly proportional to the potentials of electrochemical oxidation of aniline derivatives.     

Charge transfer complexes of methylnaphthalene derivatives with TCNE in CCl4.

The spectrophotometric and thermodynamic properties of different substituted methylnaphthalenes charge transfer (CT) complexes with tetracyanoethylene have been studied in carbon tetrachloride. The spectral characteristics of the CT bands have also been discussed in relation to the positions of methyl groups. The formation constants and the spectral properties of the complexes are markedly affected with the substitution position of the methyl groups. The ionization potentials of the donors are determined.     

Spectroscopic studies of charge transfer complexes between colchicine and some pi acceptors

Charge transfer complexes between colchicine as donor and pi acceptors such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), p-chloranil (p-CHL) have been studied spectrophotometrically in dichloromethane at 21 degrees C. The stoichiometry of the complexes was found to be 1:1 ratio by the Job method between donor and acceptors with the maximum absorption band at a wavelength of 535, 585 and 515 nm. The equilibrium constant and thermodynamic parameters of the complexes were determined by Benesi-Hildebrand and van't Hoff equations. Colchicine in pure form and in dosage form was applied in this study. The formation constants for the complexes were shown to be dependent on the structure of the electron acceptors used.     

Charge-transfer complexes of phenothiazine derivatives with π-electron acceptors

Charge-transfer complexes (CTC) of some phenothiazine derivatives with -electron acceptors were obtained. They were used to determine the ionization potentials of the investigated donor compounds. The complexing constants of phenothiazine and some of its N-substituted derivatives were found. The experimental data obtained make it possible to draw conclusions relative to their configurations.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 497–501, April, 1973.     

Charge transfer absorption for pi-conjugated polymers and oligomers mixed with electron acceptors

Pi-conjugated polymers and oligomers show charge transfer (CT) absorption bands when mixed with electron acceptors in chloroform solution. This is attributed to the formation of (ground state) donor-acceptor complexes in solution. By varying the concentration of the donor and acceptor, the extinction coefficient for the CT absorption and the association constant of donor and acceptor are estimated. The spectral position of the CT bands correlates with the electrochemical oxidation potential of the pi-conjugated donor and the reduction potential of the acceptor.     

Unexpected formation of N-fluoroalkaneacyl anilides from the reactions of fluoroalkanesulfonyl azides with nitrobenzene and its derivatives

The thermal reactions of fluoroalkanesulfonyl azides R_fCF₂SO₂N₃1 with nitrobenzene and its derivatives XC₆H₄NO₂ (X=H, F, Cl, CF₃) gave the unexpected N-fluoroalkaneacyl anilides R_fCONHC₆H₄X (X=H, Cl, F, CF₃) in addition to fluoroalkanesulfonyl amides R_fCF₂SO₂NH₂. Under the same reaction conditions, however, nitrobenzene containing an electron-donating group RC₆H₄NO₂ (R=CH₃, OCH₃) reacted with 1 affording the corresponding N-fluoroalkanesulfonyl anilides R_fCF₂SO₂NHC₆H₃(NO₂)R. Other electron-poor benzene derivatives, such as benzaldehyde, benzoate, and acetophenone C₆H₅Y(Y=CHO, COCH₃, CO₂CH₃) all gave the meta-substituted N-fluoroalkanesulfonyl anilides R_fCF₂SO₂NHC₆H₄Y.     

Charge transfer interactions between nucleic acid bases and strong acceptors

The regularities of the donor-acceptor interaction of nucleic acid bases and some of their derivatives with the strong acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) in thin amorphous films at 77 K were studied using UV and visible spectroscopy. Purine and pyrimidine bases are shown to form charge transfer TCNQ complexes whose band energies hν_ct = I_p ? E_A ? (H* ? H⁰) are linearly dependent of the donor ionization potential I_p. Calculated differences between the interaction energies of uncharged molecules and ion radicals, ΔE ≈ 3.0 eV, are in good agreement with experimental variations of the complex dissociation energies in the ground and excited states, (H* ? H⁰) = 2.73 eV. Annealing of the films of complexes containing cytosine, 1-methylcytosine, uracil, and caffeine leads to ordering of their structure and the formation of ion radical salts.     

Charge transfer complexes of electron-rich naphthalene peri-dichalcogenides with TCNQ

The electronic structures of several highly electron-rich 2,7-dimethoxynaphthalene peri-dichalcogenides were evaluated using optical and electrochemical methods, as well as by DFT calculations. Charge transfer complexes were formed with tetracyanoquinodimethane and resulted in absorption features that span from 300 nm to 1600 nm and HOMO–LUMO energy gaps as low as 0.8 eV.     

Charge transfer complexes of picolines with sigma- and pi-acceptors

In the present study CT complexes of 2-, 3- and 4-Picolines with (DDQ) 2, 3-dichloro-5, 6-dicyano parabenzoquinone (pi-acceptor) and (I(2)) Iodine (sigma-acceptor) have been investigated spectrophotometrically in three different solvents (CCl(4), CHCl(3) and CH(2)Cl(2)) at six different temperatures. The formation constants of the CT complexes were determined by the Benesi-Hildebrand equation. The thermodynamic parameters were calculated by Van(')t Hoff equation. The DeltaH degrees , DeltaG degrees and DeltaS degrees values are all negative implying that the formation of studied complexes is exothermic in nature.     

Cholesterol complexes with some proton acceptors in benzene and toluene solutions

Abstract  

Cholesterol complexes with tri-n-butyl phosphate, tri-n-octylamine, N,N-dimethylacetamide, and cyclohexanone in benzene and toluene solutions were studied using conventional IR spectroscopy. The spectra were recorded in the region of fundamental OH stretching (3,700–3,100 cm⁻¹) at 298 K. The experimental spectra were resolved into bands corresponding to the cholesterol monomer and particular oligomeric and complex species. The formation constants of complexes were determined from the-least squares plots of the linearized expressions of Bjerrum’s formation function. The stoichiometry of complexes was also identified in this way. The identification of the particular resolved bands was performed from their location, and from the dependence of their intensity on the cholesterol monomer and free base concentration.     

Cholesterol complexes with some proton acceptors in benzene and toluene solutions

Abstract  Cholesterol complexes with tri-n-butyl phosphate, tri-n-octylamine, N,N-dimethylacetamide, and cyclohexanone in benzene and toluene solutions were studied using conventional IR spectroscopy. The spectra were recorded in the region of fundamental OH stretching (3,700–3,100 cm⁻¹) at 298 K. The experimental spectra were resolved into bands corresponding to the cholesterol monomer and particular oligomeric and complex species. The formation constants of complexes were determined from the-least squares plots of the linearized expressions of Bjerrum’s formation function. The stoichiometry of complexes was also identified in this way. The identification of the particular resolved bands was performed from their location, and from the dependence of their intensity on the cholesterol monomer and free base concentration. Graphical Abstract        

Charge transfer across the water/nitrobenzene interface by three-electrode system

A droplet of aqueous solution containing a certain molar ratio of redox couple is first attached onto a platinum electrode surface, then the resulting drop electrode is immersed into the organic solution containing very hydrophobic electrolyte. Combined with reference and counter electrodes, a classical three-electrode system has been constructed. Ion transfer (IT) and electron transfer (ET) are investigated systematically using three-electrode voltammetry. Potassium ion transfer and electron transfer between potassium ferricyanide in the aqueous phase and ferrocene in nitrobenzene are observed with potassium ferricyanide/potassium ferrocyanide as the redox couple. Meanwhile, the transfer reactions of lithium, sodium, potassium, proton and ammonium ions are obtained with ferric sulfate/ferrous sulfate as the redox couple. The formal transfer potentials and the standard Gibbs transfer energy of these ions are evaluated and consistent with the results obtained by a four-electrode system and other methods.