Molecular Charge-transfer Complexes Research Articles

Charge Transfer Complex between O-Phenylenediamine and 2, 3-Dichloro-5, 6-Dicyano-1, 4-Benzoquinone: Synthesis, Spectrophotometric, Characterization, Computational Analysis, and its Biological Applications.

UV–vis electronic absorption spectroscopy was used to investigate the new molecular charge transfer complex (CTC) interaction between electron donor O-phenylenediamine (OPD) and electron acceptor 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ). The CTC solution state analysis was carried out by two different polarities. The stoichiometry of the prepared CTC was determined by using Job’s, photometric, and conductometric titration methods and was detemined to be 1:1 in both solvents (at 298 K). The formation constant and molar extinction coefficient were determined by applying the modified (1:1) Benesi–Hildebrand equation. The thermodynamic parameter ΔG° result indicated that the charge transfer reaction was spontaneous.The stability of the synthesized CTC was evaluated by using different spectroscopic parameters like the energy, ionization potential, oscillator strength, resonance energy, dissociation energy, and transition dipole moment. The synthesized solid CTC was characterized by using different analytical methods, including elemental analysis, Fourier transform infrared, nuclear magnetic resonance, TGA-DTA, and powder X-ray diffraction. The biological evolution of the charge transfer (CT) complex was studied by using DNA binding and antibacterial analysis. The CT complex binding with calf thymus DNA through an intercalative mode was observed from UV–vis spectral study. The CT complex produced a good binding constant value (6.0 × 105 L.mol–1). The antibacterial activity of the CT complex shows notable activity compared to the standard drug, tetracycline. These results reveal that the CT complex may in future be used as a bioactive drug. The hypothetical DFT estimations of the CT complex supported the experimental studies.

Synthesis, spectroscopic, and computational studies on molecular charge-transfer complex of 2-((2-hydroxybenzylidene) amino)-2-(hydroxymethyl) propane-1, 3-diol with chloranilic acid: Potential antiviral activity simulation of CT-complex against SARS-CoV-2

An innovative charge-transfer complex between the Schiff base 2-((2-hydroxybenzylidene) amino)-2-(hydroxymethyl) propane-1,3-diol [SAL-THAM] and the π-acceptor, chloranilic acid (CLA) within the mole ratio (1:1) was synthesized and characterized aiming to investigate its electronic transition spectra in acetonitrile (ACN), methanol (MeOH) and ethanol (EtOH) solutions. Applying Job`s method in the three solvents supported the 1:1 (CLA: SAL-THAM) mole ratio complex formation. The formation of stable CT- complex was shown by the highest values of charge-transfer complex formation constants, KCT, calculated using minimum-maximum absorbance method, with the sequence, acetonitrile > ethanol > methanolDFT study on the synthesized CT complex was applied based on the B3LYP method to evaluate the optimized structure and extract geometrical and reactivity parameters. Based on TD-DFT theory, the electronic properties, 1H and 13C NMR, IR, and UV-Vis spectra of the studied system in different solvents showing good agreement with the experimental studies. MEP map described the possibility of hydrogen bonding and charge transfer in the studied system. Finally, a computational approach for screening the antiviral activity of CT - complex towards SARS-CoV-2 coronavirus protease via molecular docking simulation was conducted and confirmed with molecular dynamic (MD) simulation.

Synthesis, spectroscopic and thermodynamic study of charge transfer complexes of natural drug rutin as donor with Π-acceptors; 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and tetracyanoethylene

Molecular charge-transfer complexes of the donor rutin with π-acceptors tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) were studied spectrophotometrically in two different solvents (methanol and ethanol) at three temperatures, 15, 20 and 25 °C . Formed complexes exhibit well resolved charge-transfer bands in the regions where neither donor nor acceptors have any absorption. the composition of the CTC were determined using molar ratio method and Benesi-Hildbrand equation was used to calculate the formation constants KCT and the molar extinction coefficient ɛCT of the formed CT complexes. Solid CTC were characterized by FT-IR and NMR spectroscopy. CT complexes formed in the reaction of rutin and π-acceptors DDQ and TCNE have high formation constants KCT indicating the high stability of these complexes. The latter was found to be influenced by the solvent nature, indeed, KCT values of [rut-DDQ] complex formed in ethanol are higher than those of the same complex formed in methanol, but KCT values of [rut-TCNE] complex formed in methanol are higher than those of the same complex formed in ethanol. Our results suggest the formation of stable CT complexes of rutin with π-acceptors (DDQ and TCNE).

The first representative of a new class of charge transfer complexes in o-quinone series for organic semiconductors

The first representative of a new class of charge transfer complexes for organic semiconductors was synthesized. The reaction of p-nitroaniline (PNA) with [1,10]-phenanthroline-5,6-dione (PD) results in the formation of a stable molecular charge transfer (CT) complex PNA3-PD2 in a ratio of 3:2. The structure of the molecular CT complex PNA3-PD2 was established by X-ray diffraction studies. Using the density functional theory method, it is shown that several types of intermolecular interactions are realized in the complex: between the PNA amino group and the nitro group of another PNA molecule, carbonyl groups, and PD nitrogen atoms. Complex PNA3-PD2 is stable only in solid form. The diffuse reflectance UV–vis spectrum of PNA3-PD2 crystal powder is characterized by the intense weakly structured long-wavelength absorption band up to 650 nm. Quantum chemical calculations of the electronic structure have shown that the complex PNA3-PD2 is a straight-band semiconductor with a band gap of 2.11 eV.

Toward probing of the local electron-phonon interaction in small-molecule organic semiconductors with Raman spectroscopy.

Electron-phonon interaction strongly affects and often limits charge transport in organic semiconductors (OSs). However, approaches to its experimental probing are still in their infancy. In this study, we probe the local electron-phonon interaction (quantified by the charge-transfer reorganization energy) in small-molecule OSs by means of Raman spectroscopy. Applying density functional theory calculations to four series of oligomeric OSs-polyenes, oligofurans, oligoacenes, and heteroacenes-we extend the previous evidence that the intense Raman vibrational modes considerably contribute to the reorganization energy in several molecules and molecular charge-transfer complexes, to a broader scope of OSs. The correlation between the contribution of the vibrational mode to the reorganization energy and its Raman intensity is especially prominent for the resonance conditions. The experimental Raman spectra obtained with various excitation wavelengths are in good agreement with the theoretical ones, indicating the reliability of our calculations. We also establish for the first time relations between the spectrally integrated Raman intensity, the reorganization energy, and the molecular polarizability for the resonance and off-resonance conditions. The results obtained are expected to facilitate the experimental studies of the electron-phonon interaction in OSs for an improved understanding of charge transport in these materials.

Synthesis, spectroscopic, theoretical and antimicrobial studies on molecular charge-transfer complex of 4-(2-thiazolylazo)resorcinol (TAR) with 3, 5-dinitrosalicylic acid, picric acid, and chloranilic acid

Charge-transfer complex of 4-(2-thiazolylazo) resorcinol (TAR) with 3, 5-dinitrosalicylic acid (3,5-DNSA), picric acid (PA), and chloranilic acid (CLA) were synthesized and characterized spectroscopically and investigated theoretically. Molecular composition of the prepared complexes was determined by mole ratio method. It was found that the stoichiometry of all prepared complexes is 1:2 (donor: acceptor) in methanol solvent. Stability constant of the prepared complexes were determined by using modified Benesi-Hildebrand equation. High values of formation constant of the complexes were signifying the high stability of the complexes. Different spectroscopic parameter as ionization potential (ID) of donor, oscillator strength (f), transition dipole moment (μEN), etc. were determined using UV–Vis spectroscopy in same solvent. The effect of solvent polarity on the charge-transfer spectra was also verified in four different solvents. The infrared spectrum studies of the solid complexes explore the presence of charge-transfer interaction through a hydrogen bonding interaction. TGA-DTA of the prepared complexes was also done to find out the thermal nature and stability of the complex. Synthesized complexes were checked for antibacterial and antifungal activities against different bacterial and fungal strains and complexes shows potent antibacterial and antifungal activity. DFT method was employed to view the molecular structure, electronic and spectroscopic nature of the studied complexes. MEP calculation, HOMO and LUMO energies, interaction energy, NBO analysis were performed on optimized structures of the complexes.

Electronic, infrared, mass spectrometry and thermal studies on the reaction of 2-amino-6-methylpyridine with π-acceptors

The spectrophotometric characteristics of the solid charge-transfer molecular complexes (CT) formed in the reaction of the electron donor 2-amino-6-methylpyridine (2A6MPy) with the π-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD) have been studied in chloroform at 25 °C. These were investigated through electronic and infrared spectra as well as elemental analysis.The results show that the formed solid CT-complexes have the formulas [(2A6MPy)(TCNE)2], [(2A6MPy)2(DDQ)], [(2A6MPy)4(TBCHD)] in full agreement with the known reaction stoichiometries in solution as well as the elemental measurements. The formation constant kCT, molar extinction coefficient εCT, free energy change ΔG0 and CT energy ECT have been calculated for the CT-complexes [(2A6MPy)(TCNE) 2] and [(2A6MPy)2(DDQ)].

UV–Vis, IR spectra, mass spectrometry and thermal studies of charge transfer complexes formed in the reaction of 1, 4, 8, 11-tetraazacyclotetradecane with π-electron acceptors

The solid charge-transfer (CT) molecular complexes formed in the reaction of the electron donor 1,4,8,11-tetraazacyclotetradecane (TACTD) with the π-electron acceptors 2,4,6-tetrafluoro-1,4-benzoquinone (TFQ), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD) have been investigated spectrophotometrically in chloroform at 25 °C. These were characterized through electronic and infrared spectra as well as elemental and thermal analysis. The obtained results showed that the formed solid CT-complexes have the formulas [(TACTD)(TFQ)2] and [(TACTD)(DDQ)2] and [(TACTD)(TBCHD)2] in full agreement with the known reaction stoichiometry in solution as well as the elemental measurements. The formation constant kCT, molar extinction coefficient εCT, free energy change ΔG0, CT energy ECT and the ionization potential Ip have been calculated for these CT-complexes.

Resonance Raman and UV–vis characterization of charge transfer complexes of TCNQ and aromatic amines

Although the molecular charge transfer complexes formed by 7,7,8,8-tetracyanoquinodimethane (TCNQ) and several different donors have been widely investigated in the past, in this paper it is shown for the first time the vibrational spectroscopic characterization of the complexes formed by TCNQ and the simplest series of substituted anilines in solution. The UV–vis spectra indicate the formation of TCNQ complexes stabilized by two aromatic amines in a sandwich π type complex. It was observed that the charge transfer transition energies of the complexes follow a linear correlation with the ionization potential of the amines. The resonance Raman spectra revealed, by the analysis of the ν(CC) and ν(CN) stretching modes of TCNQ, that the complexes keep their neutral character in the ground electronic state, and not as a TCNQ2− dianion species as reported before. The observed enhancement of the TCNQ bands as the amine donor capacity increases, confirmed the charge transfer nature of the electronic transitions. The DFT and TDDFT results were obtained and the theoretical Raman and electronic spectra data supported the experimental findings. The results of the model systems presented herein can contribute to a deep understanding of the photoinduced charge transfer process in complexes of TCNQ, which is a key step in the designing of organic molecular devices.

Growth and characterization of nonlinear optical crystal – Semicarbazide Picrate

Good-optical-quality single crystals of Semicarbazide Picrate (SP), a new organic charge transfer molecular complex salt, were successfully synthesized and grown by the slow evaporation solution growth technique. The grown crystal is analyzed by various instrumentation techniques. The structure of the grown crystal as determined by single crystal XRD diffraction analysis. The presence of functional groups in the SP crystals is confirmed by FT-IR vibrational analysis. The optical transparency has been studied using UV–vis spectrophotometer. The relative second harmonic generation (SHG) efficiency measurements reveal that the SP crystals is a efficient nonlinear optical (NLO) material having an activity 1.4 times as that of the reference material potassium dihydrogen phosphate. The TG/DTA thermal analyses reveal the purity of the sample and no decomposition is observed up to the melting point. The mechanical properties of the crystal are examined by Vicker's microhardness test. The dielectric permittivity, dielectric loss and AC conductivity of the crystal are measured at various temperatures.

Unusual solvent effect of molecular charge transfer complexes: Stacking/non-stacking interaction revealed by characterization of structure and photophysical aspects

The molecular charge transfer complexes using 9-methyl anthracene (9MA) and pyrene as donors and pyromellitic diimide (PMDI) as acceptor have been characterized by crystal structure analysis and photophysical studies. A π-π stacking interaction is observed in case of the 1:1 PMDI-Pyrene CT complex whereas the 1:1 PMDI-9MA CT complex exhibits selective stacking structure of the acceptor and donor in an interlock manner. The optimized structures from DFT calculations of PMDI-9MA and PMDI-Pyrene CT complexes in gas phase support the results. The photophysical studies of these complexes have been compared with the CT complexes of PMDA with four donors Naphthalene, Anthracene, Methyl Anthracene and Pyrene and the CT complexes of NTCDA with Methyl Anthracene and Pyrene. All the PMDA CT complexes exhibit blue shift of the charge transfer absorption and the corresponding emission band with increasing polarity of the solvents. This unusual solvent effect has been ascribed to specific interaction of the acceptor with the solvent. The red shift of the CT band in the solid state for the complexes compared to that observed in solvents support the contention of specific interaction. The binding constants for all the CT complexes are found to be of the order of 103 and the interplanar spacing of the stacked complexes is found to be around 3.3Å. Time resolved emissions of all the complexes reveal two different conformations in solution. The average lifetime of fluorescence in transparent KBr pellet is observed to be longer than that in solution. The structural properties, the spectral data and the geometry of the complexes in the excited states evaluated by TDDFT and DFT methods match well with the experimental results. These studies will help understand π-π interaction in supramolecular systems and in various biological interactions.

Growth, structural and characterization of a novel third order nonlinear optical Benzimidazolium Maleate single crystal

Good optical quality single crystals of Benzimidazolium Maleate (BML), a new organic charge transfer molecular complex salt, were grown successfully by the slow evaporation solution growth technique using deionised water as solvent at room temperature. The grown crystals of BML were characterised by single crystal X-ray diffraction (XRD) and powder XRD which confirm that the crystal belongs to monoclinic system with the centrosymmetric space group P21/n. The presence of functional groups in the grown crystal was confirmed by Fourier transform infrared spectral analysis. The BML crystal is thermally stable up to 147.7 °C and it is found by TG-DTA analysis. The transparency of the crystal was identified using UV–Vis spectrophotometer. Vickers microhardness analysis shows the mechanical stability of the grown crystal. The dependence of dielectric properties with frequency and temperature were also studied. Nonlinear optical absorption coefficient determined from open aperture Z-scan analysis revealed that the BML crystal can serve as a promising candidate for optical limiting applications.

Dye-Sensitized Molecular Charge Transfer Complexes: Magnetic and Conduction Properties in the Photoexcited States of Ni(dmit)2 Salts Containing Photosensitive Dyes

Photosensitive dyes often induce charge transfer (CT) between adjacent chemical species and themselves under irradiation of appropriate wavelengths. Because of the reversibility and selectivity of such CT, it is considered to be interesting to utilize such dyes as optically controllable trigger components for conduction and magnetism in the photoexcited states of organic materials. Based on this idea, such a type of new salts, i.e., γ- and δ-DiCC[Ni(dmit)2] in addition to DiCC2[Ni(dmit)2]3 have been prepared, characterized and their physical and structural properties have been examined both under dark and irradiated conditions (dmit2− = 1,3-dithiole-2-thione-4,5-dithiolate, DiCC+ = 3,3′-Dihexyloxacarbocyanine monocation). Among them, under UV (254–450 nm) irradiation, δ-DiCC[Ni(dmit)2] exhibited photoconductivity being six times as high as its dark conductivity at room temperature. The electron spin resonance (ESR) spectra have demonstrated that there are photoexcited spins on both DiCC and [Ni(dmit)2] species as a result of the CT transition between them, serving as localized spins (DiCC) and carriers ([Ni(dmit)2]), respectively. The results obtained in this work have indicated that the strategy mentioned above is effective in developing organic photoresponsive semiconductors with paramagnetism.

Synthesis, growth and characterization of o-phenylinediaminium benzilate: An SHG material with high laser damage threshold for NLO applications

An organic molecular charge transfer complex salt, o-phenylenediaminium benzilate was synthesized and single crystals grown by slow solvent evaporation solution growth technique in methanol at ambient temperature. The grown crystal was subjected to Single crystal XRD analysis to establish the molecular structure. The molecular structure was further confirmed by 1H and 13C NMR spectral studies. The formation of the charge transfer complex salt was confirmed by UV–VIS spectroscopic technique. To identify the optical transmittance window and lower wavelength cut-off, the crystal was subjected to UV–Vis–NIR transmission spectral studies. The presence of various functional groups in the salt crystal was confirmed by FT-IR spectroscopic technique. Photoluminescence study was carried out to explore its efficiency towards device fabrications. The TG and DTA thermal analyses were simultaneously carried out to establish the thermal stability of the crystal. The dielectric studies of the grown crystal were executed at different temperatures as a function of frequency to investigate its electrical properties. The SHG efficiency of the crystal was determined using the modified Kurtz and Perry powder technique and its value was found to be 1.98 times that of the KDP crystal. Laser damage threshold value was measured using Nd:YAG laser. The mechanical stability of the title crystal was established employing Vickers micro hardness tester.

The particle-hole map: Formal derivation and numerical implementation.

The particle-hole map (PHM) is a tool to visualize electronic excitations, based on representations in a canonical orbital transition space. Introduced as an alternative to the transition density matrix, the PHM has a simple probabilistic interpretation, indicating the origins and destinations of electrons and holes and, hence, the roles of different functional units of molecules during an excitation. We present a formal derivation of the PHM, starting from the particle-hole transition density matrix and projecting onto a set of single-particle orbitals. We implement the PHM using atom-centered localized basis sets and discuss the example of the molecular charge-transfer complex C2H4-C2F4.

Studies on the growth and characterization of Benzimidazolium Picrate single crystals

A new organic charge transfer molecular complex salt Benzimidazolium Picrate (BPI) single crystals were grown by slow evaporation solution growth technique using acetone as a solvent at room temperature. The grown crystals were characterised by single crystal X-ray diffraction (XRD) and powder XRD which confirm that the crystal belongs to monoclinic system with the centrosymmetric space group P21/c. The presence of functional groups in the grown crystal were confirmed by Fourier transform infrared spectrum analysis. The BPI crystal is found to be thermally stable up to 147.7 °C. The optical quality of the crystal was characterized using UV–Vis spectrophotometer. Vickers hardness study carried out at room temperature shows that the hardness increases with increase in the load. Dielectric studies were also carried out for the grown crystals. The fluorescence spectrum was recorded using spectrofluorometer. The nonlinear refractive index, nonlinear absorption coefficient and third-order nonlinear susceptibility of BPI crystal were also estimated.

Synthesis, spectrophotometric and thermodynamic studies of charge transfer complex of 5,6-dimethylbenzimidazole with chloranilic acid at various temperatures in acetonitrile and methanol solvents

Molecular charge transfer (CT) complex of donor, 5,6-dimethylbenzimidazole with acceptor, chloranilic acid was synthesized in methanol. Spectrophotometric study was performed in different solvents at different temperatures within the range of 25–45°C. 1:1 stoichiometry was determined by Benesi-Hildebrand plots. Various important thermodynamic parameters such as formation constant (KCT), molar extinction coefficient (εCT), energy of interaction (ECT), ionization potential (ID), resonance energy (RN), free energy (∆G), resonance energy (RN) oscillator strength (f), transition dipole moment (μN), enthalpy (∆H) and entropy (∆S) were determined using UV–visible spectrophotometry in different solvents at different temperatures and temperature dependency of thermodynamic parameters were also studied. FTIR, 1H NMR and ESI-MS spectroscopic techniques were used to ascertain the structure of new CT complex. The thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) determined the stability of CT complex with temperature. CT complex was formed by proton transfer from chloranilic acid to 5,6-dimethylbenzimidazole showing O–HN+ bonding.

Rational design of the solid-state synthesis of materials based on poly-aromatic molecular complexes

The possibility of exploiting a thermally-induced solid-state reaction to obtain the formation of a fluorene and TCNQ molecular complex was proposed by some of us (Kumar et al., Cryst. Growth Des., 2009, 9(8), 3396–3404). In this paper, we generalize and rationalize the approach to other charge transfer (CT) molecular complexes with naphthalene and anthracene, changing the size of the donor moiety to propose a general approach for the preparation of this class of materials by exploiting the solid-state synthesis method. Moreover, the kinetic features of the solid state reactions were fully elucidated by Raman spectroscopy and high resolution X-ray Powder Diffraction analysis (in situ Raman/XRPD), exploiting the Avrami equation in isothermal and non-isothermal conditions; rate constants, reaction orders and activation energies were obtained. All the three tested solid-state charge transfer (SS-CT) reactions obeyed a general rule, whereby the most apt reaction temperature was predicted. Finally, a method based on principal component analysis (PCA) for a fast kinetic analysis of in situ XRD synchrotron data was successfully developed, employing a formalism suitable for the analysis of non-isothermal reaction data, thus allowing a high throughput approach for the fast screening of the kinetics of parent reactions. PCA analysis was exploited as an alternative technique to obtain kinetic information in a faster and more efficient way, which can be used for online monitoring and/or in all those cases where Rietveld analysis is not feasible.

Theoretical Calculations of Molecular Charge Transfer Complexes of Aryl 2-Azomethine dibenzothiophene with Nitrobenzene Derivatives as p-Acceptors

Theoretical Calculations of Molecular Charge Transfer Complexes of Aryl 2-Azomethine dibenzothiophene with Nitrobenzene Derivatives as p-Acceptors

Charge-transfer complexes formed in the reaction of 2-amino-4-ethylpyridine with π-electron acceptors

Molecular charge-transfer complexes (CT) of electron donor 2-amino-4-ethylpyridine (2A4EPy) with π-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD) have been studied spectrophotometrically in chloroform at 25 °C. These were investigated through electronic, infrared, mass spectra and thermal measurements as well as elemental analysis. All formed complexes exhibit well resolved charge-transfer bands in the regions where neither donor nor acceptors have any absorption. The obtained results show that the formed solid CT-complexes have the structures [(2A4EPy)(TCNE)2], [(2A4EPy)2(DDQ)] and [(2A4EPy)2(TBCHD)] for 2-amino-4-ethylpyridine in full agreement with the known reaction stoichiometries in solution as well as the elemental measurements. The formation constant KCT, molar extinction coefficient εC.T, free energy change ΔG0, CT energy ECT, ionization potential Ip and oscillator strength ƒ have been calculated for these three CT-complexes.