Charge-transfer Complexes In Solution Research Articles

Procainamide Charge Transfer Complexes with Chloranilic Acid and 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone: Experimental and Theoretical Study

The formation of charge transfer (CT) complexes between bioactive molecules and/or organic molecules is an important aspect in order to understand ‘molecule-receptor’ interactions. Here, we have synthesized two new CT complexes, procainamide-chloranilic acid (PA-ChA) and procainamide-2,3-dichloro-5,6-dicyano-1,4-benzoquinone (PA-DDQ), from electron donor procainamide (PA), electron acceptor chloranilic acid (ChA), and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The structures of these two CT complexes were elucidated/characterized using FTIR, NMR, and many other spectroscopic methods. A stability study of each complex was conducted for the first time using various spectroscopic parameters (e.g., formation constant, molar extinction coefficient, ionization potential oscillator strength, dipole moment, and standard free energy). The formation of CT complexes in solution was confirmed by spectrophotometric determination. The molecular composition of each complex was determined using the spectrophotometric titration method and gave a 1:1 (donor:acceptor) ratio. In addition, the formation constant was determined using the Benesi–Hildebrand equation. To understand the noncovalent interactions of the complexes, density functional theory (DFT) calculations were performed using the ωB97XD/6-311++G(2d,p) level of theory. The DFT-computed interaction energies (ΔIEs) and the Gibbs free energies (ΔGs) were in the same order as observed experimentally. The DFT-calculated results strongly support our experimental results.

Electronic and Vibrational Manifold of Tetracyanoethylene-Chloronaphthalene Charge Transfer Complex in Solution: Insights from TD-DFT and Ab Initio Molecular Dynamics.

The interplay between light absorption and the molecular environment has a central role in the observed photophysics of a wide range of photoinduced chemical and biological phenomena. The understanding of the interplay between vibrational and electronic transitions is the focus of this work, since it can provide a rationale to tune the optical properties of charge transfer (CT) materials used for technological applications. A clear description of these processes poses a nontrivial challenge from both the theoretical and experimental points of view, where the main issue is how to accurately describe and probe drastic changes in the electronic structure and the ultrafast molecular relaxation and dynamics. In this work we focused on the intermolecular CT reaction that occurs upon photon absorption in a π-stacked model system in dichloromethane solution, in which the 1-chloronaphthalene (1ClN) acts as the electron donor and tetracyanoethylene (TCNE) is the electron acceptor. Density functional theory calculations have been carried out to characterize both the ground-state properties and more importantly the low-lying CT electronic transition, and excellent agreement with recently available experimental results [MathiesR. A.; et al. J. Phys. Chem. A2018, 122 ( (14), ), 359429558802] was obtained. The minima of the ground state and first singlet excited state have been accurately characterized in terms of spatial arrangements and vibrational Raman frequencies, and the CT natures of the first two low-lying electronic transitions in the absorption spectra have been addressed and clarified too. Finally, by modeling the possible coordination sites of the TCNE electron acceptor with respect to monovalent ions (Na+, K+) in an implicit solution of acetonitrile, we find that TCNE can accommodate a counterion in two different arrangements, parallel and orthogonal to the C=C axis, leading to the formation of a contact ion pair. The nature of the counterion and its relative position entail structural modifications of the TCNE radical anion, mainly the central C=C and C≡N bonds, compared to the isolated case. An important red shift of the C=C stretching frequency was observed when the counterion is orthogonal to the double bond, to a greater extent for Na+. On the contrary, in the second case, where the counterion ion lies along the internuclear C=C axis, we find that K+ polarizes the electron density of the double bond more, resulting in a greater red shift than with Na+.

Exploring the Franck-Condon region of a photoexcited charge transfer complex in solution to interpret femtosecond stimulated Raman spectroscopy: excited state electronic structure methods to unveil non-radiative pathways.

We present electronic structure methods to unveil the non-radiative pathways of photoinduced charge transfer (CT) reactions that play a main role in photophysics and light harvesting technologies. A prototypical π-stacked molecular complex consisting of an electron donor (1-chloronaphthalene, 1ClN) and an electron acceptor (tetracyanoethylene, TCNE) was investigated in dichloromethane solution for this purpose. The characterization of TCNE:π:1ClN in both its equilibrium ground and photoinduced low-lying CT electronic states was performed by using a reliable and accurate theoretical–computational methodology exploiting ab initio molecular dynamics simulations. The structural and vibrational time evolution of key vibrational modes is found to be in excellent agreement with femtosecond stimulated Raman spectroscopy experiments [R. A. Mathies et al., J. Phys. Chem. A, 2018, 122, 14, 3594], unveiling a correlation between vibrational fingerprints and electronic properties. The evaluation of nonadiabatic coupling matrix elements along generalized normal modes has made possible the interpretation on the molecular scale of the activation of nonradiative relaxation pathways towards the ground electronic state. In particular, two low frequency vibrational modes such as the out of plane bending and dimer breathing and the TCNE central C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C stretching play a prominent role in relaxation phenomena from the electronic CT state to the ground state one.

Macromolecular Effect Stabilized Color-Tunable and Room Temperature Charge-Transfer Complexes Based on Donor–Acceptor Assemblies

We report one of the first examples of room temperature stable solid-state charge transfer (CT) complexes based on a segmented π-conjugated polymer and rylene diimide donor–acceptor system having tunable optical transitions from the visible to NIR region in the solar spectrum. Semicrystalline and amorphous segmented oligo-phenylenevinylene (OPV) chromophore containing polymers were tailor-made with flexible polymethylene chains in the backbone. The electron rich segmented OPV polymers were complexed with two electron-deficient diimides based on naphthalene (NDI) and phenylene (PDI) core. The binary complexes of segmented OPV polymers and rylene diimides produced unique classes of CT complexes based on OPV-NDI and OPV-PDI chromophore diads. Electron microscope, polarizing microscope, and X-ray diffraction analyses provided direct evidence for the two-dimensional lamellar packing of D–A self-assembly in the solid state. Detailed absorption and emission photophysical studies revealed that the donor OPV polymers and acceptor chromophores exhibited a 1:1 complex with respect to the long-range order of D–A–D–A–D–A π-stacked supramolecular assemblies. The role of the macromolecular effect on the CT complexation was further investigated using structurally identical OPV monomers. The monomer OPV-NDI complexes (or PDI complexes) were found to exhibit CT complex in the solution; however, they underwent uncontrollable phase separation into their individual D and A crystalline domains and lost their CT self-assembly in the solid state. Interestingly, the macromolecular effect driven supramolecular self-organization of long chain segmented OPV polymers produced stable CT complexes both in solution and solid state under ambient conditions. Segmented OPV polymer + PDI and segmented OPV polymer + NDI complexes were produced as red and green colored CT complexes, respectively. This enabled the accomplishment of room temperature stable CT complexes in π-conjugated polymers having absorption ranging from 350 to 1100 nm. These donor–acceptor CT self-assemblies are processable into thin films under solvent free melt crystallization process; thus, the present segmented polymer design strategy opens up a platform for donor–acceptor CT complexes.

PAH/PAH(CF3 )n Donor/Acceptor Charge-Transfer Complexes in Solution and in Solid-State Co-Crystals.

A solution, solid‐state, and computational study is reported of polycyclic aromatic hydrocarbon PAH/PAH(CF3)n donor/acceptor (D/A) charge‐transfer complexes that involve six PAH(CF3)n acceptors with known gas‐phase electron affinities that range from 2.11(2) to 2.805(15) eV and four PAH donors, including seven CT co‐crystal X‐ray structures that exhibit hexagonal arrays of mixed π‐stacks with 1/1, 1/2, or 2/1 D/A stoichiometries (PAH=anthracene, azulene, coronene, perylene, pyrene, triphenylene; n=5, 6). These are the first D/A CT complexes with PAH(CF3)n acceptors to be studied in detail. The nine D/A combinations were chosen to allow several structural and electronic comparisons to be made, providing new insights about controlling D/A interactions and the structures of CT co‐crystals. The comparisons include, among others, CT complexes of the same PAH(CF3)n acceptor with four PAH donors and CT complexes of the same donor with four PAH(CF3)n acceptors. All nine CT complexes exhibit charge‐transfer bands in solution with λ max between 467 and 600 nm. A plot of E(λ max) versus [IE(donor)−EA(acceptor)] for the nine CT complexes studied is linear with a slope of 0.72±0.03 eV eV−1. This plot is the first of its kind for CT complexes with structurally related donors and acceptors for which precise experimental gas‐phase IEs and EAs are known. It demonstrates that conclusions based on the common assumption that the slope of a CT E(λ max) versus [IE−EA] plot is unity may be incorrect in at least some cases and should be reconsidered.

Rationally Designed Calix[4]arene–Pyrrolotetrathiafulvalene Receptors for Electron-Deficient Neutral Guests

Four upper rim bis-monopyrrolotetrathiafulvalene-calix[4]arene conjugates 2a,b and 3a,b have been efficiently synthesized using a modular construction approach. The new compounds feature a molecular tweezer architecture with a quasi-parallel arrangement of redox-active tetrathiafulvalene (TTF) arms, which serve as the guest binding centers. Complexation studies using UV/vis binding titrations revealed a high affinity of the calixarene-TTF receptors for planar electron-deficient guests, leading to formation of deeply colored charge-transfer complexes in solution. The binding efficiency of the receptors depends on the flexibility of the calixarene scaffolds and the electronic nature of the TTF arms: the highest binding efficiency is shown by receptor 2b, featuring a highly preorganized molecular structure and an electron-rich TTF moiety.

Ultrafast photoinduced dynamics of halogenated cyclopentadienes: observation of geminate charge-transfer complexes in solution

The photoinduced dynamics of the fully halogenated cyclopentadienes C5Cl6 and C5Br6 have been investigated in solution and gas phase by femtosecond time-resolved spectroscopy. Both in solution and in gas phase, homolytic dissociation into a halogen radical and a C5X5 (X = Cl, Br) radical was observed. In liquid phase, solvent-dependent formation of charge transfer complexes between geminate radicals was observed for the first time. These complexes were found to be surprisingly stable and offered the opportunity to follow the dynamics of specific radical pairs. In the case of C5Cl6 in trichloroethanol, a reaction of the chlorine radical with molecules from the solvent cage was observed.

Geometry and quadratic nonlinearity of charge transfer complexes in solution using depolarized hyper-Rayleigh scattering

We report large quadratic nonlinearity in a series of 1:1 molecular complexes between methyl substituted benzene donors and quinone acceptors in solution. The first hyperpolarizability, β(HRS), which is very small for the individual components, becomes large by intermolecular charge transfer (CT) interaction between the donor and the acceptor in the complex. In addition, we have investigated the geometry of these CT complexes in solution using polarization resolved hyper-Rayleigh scattering (HRS). Using linearly (electric field vector along X direction) and circularly polarized incident light, respectively, we have measured two macroscopic depolarization ratios D=I(2ω,X,X)/I(2ω,Z,X) and D(')=I(2ω,X,C)/I(2ω,Z,C) in the laboratory fixed XYZ frame by detecting the second harmonic scattered light in a polarization resolved fashion. The experimentally obtained first hyperpolarizability, β(HRS), and the value of macroscopic depolarization ratios, D and D('), are then matched with the theoretically deduced values from single and double configuration interaction calculations performed using the Zerner's intermediate neglect of differential overlap self-consistent reaction field technique. In solution, since several geometries are possible, we have carried out calculations by rotating the acceptor moiety around three different axes keeping the donor molecule fixed at an optimized geometry. These rotations give us the theoretical β(HRS), D and D(') values as a function of the geometry of the complex. The calculated β(HRS), D, and D(') values that closely match with the experimental values, give the dominant equilibrium geometry in solution. All the CT complexes between methyl benzenes and chloranil or 1,2-dichloro-4,5-dicyano-p-benzoquinone investigated here are found to have a slipped parallel stacking of the donors and the acceptors. Furthermore, the geometries are staggered and in some pairs, a twist angle as high as 30° is observed. Thus, we have demonstrated in this paper that the polarization resolved HRS technique along with theoretical calculations can unravel the geometry of CT complexes in solution.

Geometry and quadratic nonlinearity of charge transfer complexes in solution: A theoretical study

In this paper, we have computed the quadratic nonlinear optical (NLO) properties of a class of weak charge transfer (CT) complexes. These weak complexes are formed when the methyl substituted benzenes (donors) are added to strong acceptors like chloranil (CHL) or di-chloro-di-cyano benzoquinone (DDQ) in chloroform or in dichloromethane. The formation of such complexes is manifested by the presence of a broad absorption maximum in the visible range of the spectrum where neither the donor nor the acceptor absorbs. The appearance of this visible band is due to CT interactions, which result in strong NLO responses. We have employed the semiempirical intermediate neglect of differential overlap (INDO∕S) Hamiltonian to calculate the energy levels of these CT complexes using single and double configuration interaction (SDCI). The solvent effects are taken into account by using the self-consistent reaction field (SCRF) scheme. The geometry of the complex is obtained by exploring different relative molecular geometries by rotating the acceptor with respect to the fixed donor about three different axes. The theoretical geometry that best fits the experimental energy gaps, β(HRS) and macroscopic depolarization ratios is taken to be the most probable geometry of the complex. Our studies show that the most probable geometry of these complexes in solution is the parallel displaced structure with a significant twist in some cases.

Formation of Specific Charge-transfer Complexes between Hyperbranched Polymer Viologen and Neutral Donors in Solid Films Depending on Donor Fraction

Abstract Neutral donors and hyperbranched polymer with many viologen groups formed charge-transfer complexes in solutions and solid films. The charge-transfer absorption and fluorescence spectra showed red shifts with increasing donor fractions only in the case of polymer solid films, strongly suggesting solvatochromism in solid films and formation of multichromophore CT complex. These are unique microenvironmental effects of the present cationic polymer.

Spectrophotometric study of interaction of iodine with 4′-aminobenzo-15-crown-5 in chloroform, dichloromethane and 1,2-dichloroethane solutions

The formation of charge transfer complex between 4′-aminobenzo-15-crown-5 (AB15C5) and iodine is investigated spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 °C. The continuous variation method clearly revealed the formation of 1:1 charge transfer complex in solution. The observed time dependence of the charge transfer band and subsequent formation of I 3 − in solution were related to the slow transformation of the initially formed 1:1 AB15C5·I 2 outer complex to an inner electron donor–acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The pseudo-first-order rate constants for the transformation process were evaluated from the absorbance–time data and found to vary in the order of 1,2-DCE > DCM > CHCl 3. The values of the formation constant, K DA, for each complex are evaluated from Benesi–Hilebrand equation. Stability of the resulting complex in three solvents was also found to vary in the order of 1,2-DCE > DCM > CHCl 3.

Flexible alteration of optical nonlinearities of iodine charge-transfer complexes in solutions.

The type of donor used is found to influence greatly the optical nonlinearities of iodine charge-transfer (CT) complexes in solutions for several solvents. The magnitude and sign changes of nonlinear absorption of iodine CT complexes for different solvents as donors are observed, which implies the transition from saturable absorption to reverse saturable absorption. Compared with C60 in toluene, iodine CT complexes with toluene and benzene demonstrate larger reverse saturable absorption. Meanwhile, flexible alteration of optical nonlinearities is easily obtained by adjusting the mixture ratio of different solvents, yielding a prospective means of constructing a nonlinear medium with a large nonlinear coefficient.

Synthesis and properties of a series of new asymmetrical tetrathiafulvalene derivatives

A series of new asymmetrically substituted tetrathiafulvalene (TTF) derivatives, a charge transfer (CT) complex, and several related symmetrical TTF derivatives were synthesized. The compounds were characterized by elemental analysis, 1H NMR spectra, IR spectra, and electron ionization (EI) or negative-ion fast atom bombardment (FAB) mass spectral analysis. UV-Vis spectra of the new asymmetrical TTF derivatives and the CT complex in solution were investigated. In addition, mixed conducting Langmuir-Blodgett (LB) films were constructed from the asymmetrical TTF derivatives by admixing with an equimolar arachidic acid.

On the structure of iodine charge-transfer complexes in solution

Femtosecond transient absorption studies of charge-transfer complexes of I 2 with hexamethylbenzene have been performed in a series of noncomplexing solvents. Anisotropy measurements of the bleach of the charge-transfer absorption band indicate that the geometry and electronic structure of the complex is dependent upon the solvent environment. The results are interpreted as favoring an oblique, nearly axial, geometry in alkanes and a resting geometry in chlorinated methanes.

Low-frequency electrical conductivity of poly(phenylacetylene)-iodine in tetrahydrofuran solutions: effect of iodine concentration

The electrical conductivity of poly(phenylacetylene)-iodine in tetrahydrofuran solution has been measured at the frequency of 10 kHz, in the temperature range from −15 to 40 °C as a function of iodine concentration. The data have been analysed on the basis of the counterion fluctuation model developed for highly charged polyelectrolyte aqueous solutions. The dependence of the electrical conductivity on the iodine concentration suggests that the conduction mechanism is governed by the interaction of the polymer with iodine molecules, resulting in a charge-transfer complex in solution, the effectiveness of which is maximum at some well-defined concentrations corresponding to six polymer units for each I 5 − ion.

A picosecond diffuse reflectance laser photolysis study on phenanthrene—pyromellitic dianhydride charge-transfer crystal

Picosecond transient absorption spectra of phenanthrene—pyromellitic dianhydride (PMDA) charge-transfer (CT) crystal were measured for the first time, and the high CT nature of the S 1 state was directly confirmed. The formation process of the CT state was completed within a few ps and dependent upon the excitation wavelength. The electronic structure and dynamics were discussed by comparing the results with those of the CT complex in solution.

Temperature dependence of low-frequency electrical conductivity of the poly(phenylacetylene)-iodine charge-transfer complex in solution

The electrical conductivity of poly(phenylacetylene)-iodine in tetrahydrofuran solutions has been measured at the frequency of 10 kHz, in the temperature range from − 15 to 40 °C. The data have been analysed in the light of current theories of polyelectrolyte solutions, considering the effect of counterions along the charged polymer chain. Our results show a linear dependence of electrical conductivity on the polymer concentration at an I 2 doping concentration of 10 mg/ml. These data can be accounted for by considering an electronic charge distributed over, on average, a polymer segment containing six monomers.

Femtosecond-picosecond laser photolysis studies on the dynamics of excited charge-transfer complexes in solution. 3. Dissociation into free ions and charge recombination decay from the ion-pair state formed by charge separation in the excited state of 1,2,4,5-tetracyanobenzene-aromatic hydrocarbon complexes in polar solvents

Femtosecond-picosecond laser photolysis studies on the dynamics of excited charge-transfer complexes in solution. 3. Dissociation into free ions and charge recombination decay from the ion-pair state formed by charge separation in the excited state of 1,2,4,5-tetracyanobenzene-aromatic hydrocarbon complexes in polar solvents

Femtosecond-picosecond laser photolysis studies on the dynamics of excited charge-transfer complexes in solution. 2. Ion pair formation processes in the excited states of 1,2,4,5-tetracyanobenzene-aromatic hydrocarbon complexes in polar solvents

Femtosecond and picosecond laser photolysis and time-resolved transient absorption spectral studies have been made-to elucidate the photoinduced charge separation (CS) process in the 1,2,4,5-tetracyanobenzene (TCNB)-aromatic hydrocarbon charge-transfer (CT) complexes in various polar solvents. We have confirmed that, in a polar solvent such as acetonitrile, solvent reorientation can induce CS with a time constant shorter than 1 ps to a considerable extent but not completely. Moreover, we have demonstrated that, for the complete CS leading to the ion-pair formation, further intracomplex structural change and solvation, which take place with a time constant (τ CS ) of several picoseconds to 30 ps depending on the natures of the electron-donating aromatic hydrocarbon and the polar solvent, are necessary

Femtosecond-picosecond laser photolysis studies on the dynamics of excited charge-transfer complexes in solution. 1. Charge separation processes in the course of the relaxation from the excited Franck-Condon state of 1,2,4,5-tetracyanobenzene in benzene and methyl-substituted benzene solutions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFemtosecond-picosecond laser photolysis studies on the dynamics of excited charge-transfer complexes in solution. 1. Charge separation processes in the course of the relaxation from the excited Franck-Condon state of 1,2,4,5-tetracyanobenzene in benzene and methyl-substituted benzene solutionsSeishi. Ojima, Hiroshi. Miyasaka, and Noboru. MatagaCite this: J. Phys. Chem. 1990, 94, 10, 4147–4152Publication Date (Print):May 1, 1990Publication History Published online1 May 2002Published inissue 1 May 1990https://doi.org/10.1021/j100373a050RIGHTS & PERMISSIONSArticle Views178Altmetric-Citations57LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (751 KB) Get e-Alerts