Synthesis and spectroscopic studies of charge transfer complex between dihydroxy-p-benzoquinone and 4-dimethylaminopyridine in different solvents

Charge transfer (CT) complex formation between 4-dimethylaminopyridine (4-DMAP) as the electron donor and 2,5-dihydroxy-p-benzoquinone (DHBQ) as the π-electron acceptor has been investigated spectrophotometrically in methanol (MeOH), ethanol (EtOH) and acetonitrile (AN). The stoichiometry of the complex has been identified by Job’s and photometric titration methods to be 1:1. The Benesi–Hildebrand equation has been applied to estimate the formation constant (K_CT) and molecular extinction coefficient (ε). It was found that the value of K_CT is larger in AN than in MeOH and EtOH. The thermodynamic parameters are in agreement with the K_CT values in that the enthalpy of formation (?ΔH) has a larger value both in EtOH and MeOH than in AN, suggesting higher stability of the complex in EtOH. The complex formed between 4-DMAP and DHBQ has been isolated as a solid and characterised using elemental analysis, FTIR and ¹H NMR measurements. Moreover, it has been found that the formed complex involves proton transfer in addition to CT.     

Spectroscopic,thermal studies and molecular modelling of charge transfer complexation between 5-amino-2-methoxypyridine with chloranilic acid in different polar solvents

Charge transfer (CT) interaction between 5-amino-2-methoxypyridine (5AMPy), as electron donor (proton acceptor), with 3,6-dichloro-2,5-dihydroxy-p-benzoquinone (chloranilic acid, H₂CA), as electron acceptor (proton donor), has been investigated spectrophotometrically in the polar protic solvents ethanol (EtOH) and methanol (MeOH) and the aprotic one acetonitrile (AN). Pink-coloured solution is formed instantaneously upon mixing 5AMPy with H₂CA solutions in all solvents, which is the hallmark evidence of CT complex formation. Based on Job’s method of continuous variations, as well as spectrophotometric titrations, the stoichiometry of the complex was found to be 1:1 [(5AMPy) (H₂CA)] in all solvents. Benesi–Hildebrand equation has been applied to estimate the formation constant of the produced CT complex (K_CT) and its molar absorptivity (ε), they reached high values, confirming the complex high stability. Solid CT complex has been synthesised and analysed by elemental analyses and FTIR, ¹H NMR spectroscopies, where 2:1 [(5AMPy)₂ (H₂CA)] CT complex was obtained.     

Spectrophotometric study of charge transfer complex between 2,6-diaminopyridine and 2,5-dihydroxy-p-benzoquinone

Charge transfer (CT) complex formation between 2,6-diaminopyridine (2,6-DAP) as the electron donor with 2,5-dihydroxy-p-benzoquinone (DHBQ) as the electron acceptor has been studied spectrophotometrically in different polar solvents at room temperature. A new absorption band due to CT complex formation was observed near 490?nm. The stoichiometric ratio of the complex has been identified by Job's, photometric and conductometric titration methods to be 1?:?1. Benesi–Hildebrand equation has been applied to estimate the formation constant (K _CT) and molecular extinction coefficient (ε). They recorded high values confirming high stability of the formed complex. The physical parameters, oscillator strength (f), transition dipole moment (μ), ionisation potential (I _D), resonance energy (R_N ) and standard free energy change (ΔG°) of the formed complex were determined and evaluated in the different solvents. The solid complex between 2,6-DAP and DHBQ has been isolated and characterised using elemental analysis, FT-IR and ¹H-NMR measurements.     

Spectroscopic and Thermodynamic Studies on Charge Transfer Complex Formation between 2-Aminopyridine and 2,5-Dihydroxy-<Emphasis Type="Italic">p</Emphasis>-benzoquinone

Charge transfer complex formation between 2-aminopyridine (2AP) as the electron donor with 2,5-dihydroxy-p-benzoquinone (AHBQ) as the π-electron acceptor has been investigated spectrophotometrically in acetonitrile (AN) and 50% acetonitrile + 50% 1,2-dichloroethane (V/V), (ANDC). The stoichiometry of the complex has been identified by Job’s method to be 1:1. The Benesi-Hildebrand equation has been applied to estimate the formation constant (K _CT) and molecular extinction coefficient (ε). It was found that the value of K _CT is larger in ANDC than in AN. The thermodynamic parameters are in agreement with the K _CT values in that the enthalpy of formation (−ΔH) has a larger value in ANDC than in AN, suggesting higher stability of the complex in ANDC. The complex formed between 2AP and DHBQ has been isolated as a solid and characterized using elemental analysis, FTIR, and ¹H NMR measurements. Moreover, it has been found that the formed complex involves proton transfer in addition to charge transfer.     

Spectrophotometric and spectroscopic studies of charge transfer complexes of p-toluidine as an electron donor with picric acid as an electron acceptor in different solvents

The charge transfer complexes of the donor p-toluidine with π-acceptor picric acid have been studied spectrophotometrically in various solvents such as carbon tetrachloride, chloroform, dichloromethane acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in non-polar solvent is high. The stoichiometry of the complex was found to be 1:1 ratio by straight-line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant (K_CT), molar extinction coefficient (?_CT), standard free energy (ΔG^o), oscillator strength (f), transition dipole moment (μ_EN), resonance energy (R_N) and ionization potential (I_D). The results indicate that the formation constant (K_CT) for the complex was shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents that were used.     

Synthesis and spectroscopic studies of the charge transfer complexes of 2- and 3-aminopyridine

The interactions of the electron donors 2-aminopyridine (2APY) and 3-aminopyridine (3APY) with the π-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2-chloro-1,3,5-trinitrobenzene (picryl chloride, PC), and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge transfer (CT) complexes were recorded. Photometric titration showed that the stoichiometries of the reactions were fixed and depended on the nature of both the donor and the acceptor. The molecular structures of the CT-complexes were, however, independent of the position of the amino group on the pyridine ring and were formulated as [(APY)(TCNE)], [(APY)(DDQ)], [(APY)(PC)], and [(APY) (chloranil)]. The formation constants (K_CT), charge transfer energy (E_CT) and molar extinction coefficients (_CT) of the formed CT-complexes were obtained.     

Spectroscopic studies of multiple charge transfer complexes of p-toluidine with π-acceptor picric acid in different polar solvents

The charge transfer complexes of the donor p-toluidine with π-acceptor picric acid have been studied spectrophotometrically in various solvents such as acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in less polar solvent is high. The stoichiometry of the complex was found to be 1: 1 ratio by straight line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant (K _CT), molar extinction coefficient (?_CT), standard free energy (ΔG°), oscillator strength (f), transition dipole moment (μ_EN), resonance energy (R _N) and ionization potential (I _D). The results indicate that the formation constant (K _CT) for the complex were shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents which were used.     

Spectrophotometric and spectroscopic studies of complexation of 8-hydroxyquinoline with π acceptor metadinitrobenzene in different polar solvents

The complexation of electron donor–acceptor complexes of 8-hydroxyquinoline (8HQ) and metadinitrobenzene (MNB) have been studied spectrophotometrically and thermodynamically in different polar solvent at room temperature. A new absorption band due to charge transfer (CT) transition is observed in the visible region. A new theoretical model has been developed which take into account the interaction between electronic subsystem of 8HQ and MNB. The results indicate the extent of charge transfer complexes (CTCs) formation to be more in less polar solvents. Stoichiometry of the complex was found to be 1:1 by straight line method and ¹H NMR between donor and acceptor at the maximum absorption bands. Ionization potential (I_D) and resonance energy (R_N) were determined from the CT transition energy in different solvents. The formation constants of the complexes were determined in different polar solvents from which ΔG° formation of the complexes was estimated and also extinction coefficient of the charge transfer complex (CTC) was calculated. Oscillator strength, transition dipole strengths and maximum wavelength of the CTC (λ_CT) in various solvents and IR spectra of the CTC have also been discussed. It has been observed that all parameters described above changed with change in polarity and concentration of donor.     

The Charge Transfer Complex between 2, 3-diamino-5-bromopyridine and Chloranilic acid: Preparation,Spectroscopic Characterization,DNA binding,and DFT/PCM analysis

A charge transfer hydrogen bonded complex was prepared and experimentally explored in an acetonitrile (ACN) medium between the proton acceptor (electron donor) 2, 3-Diamino-5-bromopyridine and the proton donor (electron acceptor) chloranilic acid. The stoichiometry of the charge transfer complex is 1:1. The Benesi-Hildebrand equation is used to calculate the molar absorptivity (ε_CT), association constant (K_CT) and other spectroscopic physical characteristics. The solid compound was synthesized and studied using several spectroscopic methods. The presence of charge and proton transfers in the resultant complex was supported by ¹H NMR, FT-IR and SEM-EDX investigations. The complex DNA binding ability was investigated using electron absorption spectroscopy, and the CT complex binding mechanism is intercalative. The intrinsic binding constant (K_b) value is 5.2 × 10⁶M?1. The good binding affinity of the CT complex makes it potentially suitable for usage as a pharmaceutical in the future. Molecular docking calculations have been performed between CT complex and DNA (ID = 1BNA) to study the CT-DNA interaction theoretically. To corroborate the experimental findings, calculations based on DFT were carried out in the gas and PCM analysis where the existence of charge and hydrogen transfers. Finally, good agreement between experimental and theoretical computations was observed confirming that the basis set used is appropriate for the system under examination.     

Preparation and Spectroscopic Studies of Charge-Transfer Complexes of Thiamine Hydrochloride with Different Electron Acceptor

Abstract—Electronic interactions associated with charge transfer complexes formation of iodine, chloranilic acid (H₂CA) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) with vitamin B1 have been studied spectrophotometrically. The accumulated data indicated formation of CT-complexes of the general formula [(VB1)(acceptor) _n ], (n = 1 or 2). The 1 : 2 and 1 : 1 donor: acceptor molar ratios were calculated on the basis of elemental analysis and photometric titrations. The solid complexes were prepared and characterized by their conductivity, UV-Vis, IR, and ¹H NMR spectra, and thermogravimetric analyses (TGA, DTG). The characteristic physical constants (K_CT, ε_CT, μ, ΔG, I_p, f, E_CT) of the formed CT-complexes were determined to be strongly dependent on nature of the electron acceptors.

     

Charge transfer complexes beneficial method for determination of fluoxetine HCl pure drug: Spectroscopic and thermal analyses discussions

A simple and conventional spectrophotometric method is developed for quantitative analysis of fluoxetine. The method is based on the charge transfer 1: 1 complex formation of fluoxetine hydrochloride with electron acceptors: picric acid, dinitrobenzene, p-nitrobenzoic acid, 2,6-dichloroquinone-4-chloroimide, 2,6-dibromoquinone-4-chloroimide and 7,7′,8,8′-tetracyanoquinodimethane. The charge-transfer complexes are isolated and characterized by elemental analysis, conductivity, IR, Raman, ¹H NMR spectra, X-ray powder diffraction, scanning electron microscopy and thermogravimetric analysis. The formation constants (K _CT), molar extinction coefficients (?_CT), standard free energies (ΔG ⁰), oscillator strengths (f), dipole moments (μ), resonance energies (R _N) and ionization potentials (I _D) are estimated. Thermodynamic parameters were computed from the thermal decomposition data.     

New Charge Transfer Complexes of K+-Channel-Blocker Drug (Amifampridine; AMFP) for Sensitive Detection; Solution Investigations and DFT Studies

UV–Vis spectroscopy was used to investigate two new charge transfer (CT) complexes formed between the K⁺-channel-blocker amifampridine (AMFP) drug and the two π-acceptors 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetracyanoethylene (TCNE) in different solvents. The molecular composition of the new CT complexes was estimated using the continuous variations method and found to be 1:1 for both complexes. The formed CT complexes’ electronic spectra data were further employed for calculating the formation constants (K_CT), molar extinction coefficients (ε_CT), and physical parameters at various temperatures, and the results demonstrated the high stability of both complexes. In addition, sensitive spectrophotometric methods for quantifying AMFP in its pure form were proposed and statistically validated. Furthermore, DFT calculations were used to predict the molecular structures of AMFP–DDQ and AMFP–TCNE complexes in CHCl₃. TD-DFT calculations were also used to predict the electronic spectra of both complexes. A CT-based transition band (exp. 399 and 417 nm) for the AMFP–TCNE complex was calculated at 411.5 nm (f = 0.105, HOMO-1 → LUMO). The two absorption bands at 459 nm (calc. 426.9 nm, f = 0.054) and 584 nm (calc. 628.1 nm, f = 0.111) of the AMFP–DDQ complex were theoretically assigned to HOMO-1 → LUMO and HOMO → LUMO excitations, respectively.     

Charge Transfer Complexes of Some Heterocyclic Aromatic Amines with π‐Organic Acceptors in Polar Solvents

A conductometric titration technique has been used to investigate the electron transfer activity of CT molecular complexes formed by arylazopyrimidine and naphthylazopyrimidine derivatives as donors and the organic π‐acceptors p‐nitroaniline, p‐chloroaniline, p‐bromoaniline, anthraquinone, picric acid, α‐nitroso‐β‐naphthol, p‐hydroxybenzaldehyde and maleic anhydride. The study was performed at different degree of temperature and in three different polar solvents namely N,N‐dimethylformamide (DMF), acetonitrile (ACN) and dimethylsulfoxide (DMSO). The stoichiometric ratios of these complexes were found to be 1:1. The dissociation constant (ασ_M) values of the formed complexes have been calculated, and the effects of solvents as well as types of electron donors on their conductance σ_p‐values have been examined.     

Spectrophotometric studies of the formation of charge transfer complex of iron(III) with N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane di-Schiff base ligand in methanol

The complex formation reaction between N,N′-bis(2-pyridylmethylidene)-1,2-diiminoethane (BPIE) di-Schiff base ligand as an electron donor and iron(III) chloride as an electron acceptor have been studied spectrophometrically in methanol at 28°C. The values of equilibrium constants, K and molar absorptivities, ε were obtained from the Benesi–Hildebrand, Scott and Foster–Hammick–Wardley equations. The results indicate the formation of 1?:?1 charge transfer complex. The absorption band energy of the complex, E _CT, the ionization potential of the BPIE Schiff base ligand, I ^D, and the Gibbs energy changes of the above reaction, ΔG ⁰, were calculated. Finally, the kinetics of the complex formation reaction were studied and was found to be second-order in each reactant. The values of the rate constants of the forward and reverse reactions k ₁ and k _?1 were determined.     

Electronic Spectroscopic Studies of the Charge Transfer Complex of N,N , N ′, N ′-Tetramethyl-4-4′-Diamino-Benzophenone with Iodine in Methanol

The UV-visible absorption bands of the charge transfer (CT) complex of N, N, N', N'-tetramethyl-4,4'-diamino-benzophenone with iodine in methanol at 30°C have been studied. The value of K^AD , ?^AD and E _CT were calculated for this complex. The value of the equilibrium constant, K^AD , for the above complex reaction was calculated as 28.85m³·mol^?1. The value of the molar extinction coefficient of the CT complex, ?^AD , was also calculated as 1171m²·mol^?1 for λ_max = 602 nm and the absorption band energy E _CT of the complex was found to be 2.06 e.v. The ionization potential of the electron donor was also obtained spectroscopically and found to be 6.284 e.v. The rate constant obtained for the forward reaction is 3.624 x 10^?5M^1/2s^?1 and for the reverse reaction is 1.256 x 10^?6s^?1. Finally, the half-life value for the above reaction was graphically calculated and shown to be 1.549 day. The kinetics of the above reaction were studied showing the reaction to be a half-order reaction. The values of rate constants and half-life were calculated.     

Vectorial Electron Transfer in Donor–Photosensitizer–Acceptor Triads Based on Novel Bis‐tridentate Ruthenium Polypyridyl Complexes

The first examples of rodlike donor–photosensitizer–acceptor arrays based on bis‐2,6‐di(quinolin‐8‐yl)pyridine Ru^II complexes 1 a and 3 a for photoinduced electron transfer have been synthesized and investigated. The complexes are synthesized in a convergent manner and are isolated as linear, single isomers. Time‐resolved absorption spectroscopy reveals long‐lived, photoinduced charge‐separated states (τ_CSS ( 1 a )=140 ns, τ_CSS ( 3 a )=200 ns) formed by stepwise electron transfer. The overall yields of charge separation (≥50 % for complex 1 a and ≥95 % for complex 3 a ) are unprecedented for bis‐tridentate Ru^II polypyridyl complexes. This is attributed to the long‐lived excited state of the [Ru(dqp)₂]²⁺ complex combined with fast electron transfer from the donor moiety following the initial charge separation. The rodlike arrangement of donor and acceptor gives controlled, vectorial electron transfer, free from the complications of stereoisomeric diversity. Thus, such arrays provide an excellent system for the study of photoinduced electron transfer and, ultimately, the harvesting of solar energy.     

The Polymerization and Oxidation of Pyrrole by Halogens in Organic Solvents

Simultaneous chemical polymerization and oxidation of pyrrole have been initiated by a halogenic electron acceptor, bromine or iodine, in various organic solvents. The polypyrrole (PPY)-halogen charge transfer (CT) complexes obtained from polymerization in acetonitrile are of particular interest. Both the PPY-I₂ and PPY-Br₂ CT complexes are granular in nature and have an electrical conductivity in the order of 1 to 10 ohm^?1 cm^?1. Both complexes show remarkable stability in the atmosphere and in the presence of moisture. The PPY-I₂ and PPY-Br₂ CT complexes in the form of thin, coarse films have also been synthesized on a SnO₂ electrode by electrochemical polymerization in acetonitrile. The physicochemical properties of the PPY-I₂ and PPY-Br₂ CT complexes prepared by the chemical methods are characterized by means of UV-visible and IR absorption spectroscopy, thermal and chemical analysis, and electrical conductivity and density measurements.     

Spektroskopische und theoretische Untersuchungen zum Interligand-Charge-Transfer in Gemischtligandenkomplexen des Nickel(II) mit Dithiolat- undα-Diiminliganden

Spectroscopic and Theoretical Investigations of the Interligand Charge Transfer of Nickel(II) Mixed Ligand Complexes with Dithiolate and α-Diimine Ligands Nickel(II) mixed ligand complexes with dithiolate and α-diimine ligands are characterized by an unusual interligand charge transfer (LL′CT) band of medium intensity in the visible region. Based on spectroscopic and quantum chemical investigations, possibilities of shifting the absorption maximum of the LL′CT band depending on the acceptor and donor ligand are discussed. For the [Ni(mnt)N, N] system, with mnt = maleonitriledithiolate a maximum spectral shift of Δν = 6 480 cm^?1 is obtained (N, N = diacetyldihydrazone: ν _CT = 21230 cm^?1; N, N = phenanthrenequinone diimine: ν _CT = 14750 cm^?1). The influence of solvent polarity on the energy of the interligand band has been investigated in detail for two selected compounds, correlations with E_T parameters of Reichardt were found.     

Spectroscopic studies of charge transfer complexes of meso‐tetra‐p‐tolylporphyrin and its zinc complex with some aromatic nitro acceptors in different organic solvents

The charge transfer complex (CTC) formation of 5,10,15,20‐tetra(p‐tolyl)porphyrin (TTP) and zinc 5,10,15,20‐tetra(p‐tolyl)porphyrin with some aromatic nitro acceptors such as 2,4,6‐trinitrophenol (picric acid), 3,5‐dinitrosalicylic acid, 3,5‐dinitrobenzoic acid (DNB) and 2,4‐dinitrophenol (DNP) was studied spectrophotometrically in different organic solvents at different temperatures. The spectrophotometric titration, Job's and straight line methods indicated the formation of 1:1 CTCs. The values of the equilibrium constant (K_CT) and molar extinction coefficient (ε_CT) were calculated for each complex. The ionization potential of the donors and the dissociation energy of the charge transfer excited state for the CTC in different solvents was also determined and was found to be constant. The spectroscopic and thermodynamic properties were observed to be sensitive to the electron affinity of the acceptors and the nature of the solvent. No CT band was observed between Zn‐TTP as donor and DNP or DNB as acceptors in various organic solvents at different temperature. Bimolecular reactions between singlet excited TTP (¹TTP*) and the acceptors were investigated in solvents with various polarities. A new emission band was observed. The fluorescence intensity of the donor band decreased with increasing the concentration of the acceptor accompanied by an increase in the intensity of the new emission. The new emission of the CTCs can be interpreted as a CT excited complex (exciplex). Copyright © 2007 John Wiley & Sons, Ltd.     

Contrasting Effects of Axial Ligands on Electron‐Transfer Versus Proton‐Coupled Electron‐Transfer Reactions of Nonheme Oxoiron(IV) Complexes

The effects of axial ligands on electron‐transfer and proton‐coupled electron‐transfer reactions of mononuclear nonheme oxoiron(IV) complexes were investigated by using [Fe^IV(O)(tmc)(X)]ⁿ⁺ ( 1 ‐X) with various axial ligands, in which tmc is 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane and X is CH₃CN ( 1 ‐NCCH₃), CF₃COO^? ( 1 ‐OOCCF₃), or N₃^? ( 1 ‐N₃), and ferrocene derivatives as electron donors. As the binding strength of the axial ligands increases, the one‐electron reduction potentials of 1 ‐X (E_red, V vs. saturated calomel electrode (SCE)) are more negatively shifted by the binding of the more electron‐donating axial ligands in the order of 1 ‐NCCH₃ (0.39) > 1 ‐OOCCF₃ (0.13) > 1 ‐N₃ (?0.05 V). Rate constants of electron transfer from ferrocene derivatives to 1 ‐X were analyzed in light of the Marcus theory of electron transfer to determine reorganization energies (λ) of electron transfer. The λ values decrease in the order of 1 ‐NCCH₃ (2.37) > 1 ‐OOCCF₃ (2.12) > 1 ‐N₃ (1.97 eV). Thus, the electron‐transfer reduction becomes less favorable thermodynamically but more favorable kinetically with increasing donor ability of the axial ligands. The net effect of the axial ligands is the deceleration of the electron‐transfer rate in the order of 1 ‐NCCH₃ > 1 ‐OOCCF₃ > 1 ‐N₃. In sharp contrast to this, the rates of the proton‐coupled electron‐transfer reactions of 1 ‐X are markedly accelerated in the presence of an acid in the opposite order: 1 ‐NCCH₃ < 1 ‐OOCCF₃ < 1 ‐N₃. Such contrasting effects of the axial ligands on the electron‐transfer and proton‐coupled electron‐transfer reactions of nonheme oxoiron(IV) complexes are discussed in light of the counterintuitive reactivity patterns observed in the oxo transfer and hydrogen‐atom abstraction reactions by nonheme oxoiron(IV) complexes (Sastri et al. Proc. Natl. Acad. Sci. U.S.A. 2007 , 104, 19 181–19 186).