Aromatic hydrocarbon-carbonium ion molecular complexes

Molecular complexes of aromatic hydrocarbons and carbonium ions are described according to Mulliken's donor — acceptor theory. Estimations of electron affinities of several cations are deduced from charge-transfer transition energies and the indepently measured electron affinity of the tropylium ion.     

Preparation and spectroscopic studies on charge-transfer complexes of 2,2'-bipyridine with picric and chloranilic acids

Charge-transfer (CT) complexes formed on the reaction of 2,2'-bipyridine with some acceptors such as picric acid (HPA) and chloranilic acid (H(2)CA) have been studied in CHCl(3) and MeOH at room temperature. Based on elemental analysis and IR spectra of the solid CT complexes along with the photometric titration curves for the reactions, the data obtained indicate the formation of 1:1 charge-transfer complexes [(bpyH)(PA)] and [(bpyH(2))(CA)], respectively. The infrared and (1)H NMR spectroscopic data indicate a charge-transfer interaction associated with a proton migration from the acceptor to the donor followed by intramolecular hydrogen bonding. The formation constants (K(C)) for the complexes were shown to be dependent on the structure of the electron acceptors used.     

Synthesis and electrochemical studies of charge-transfer complexes of thiazolidine-2,4-dione with σ and π acceptors

In the present work, we report the synthesis and characterization of novel charge-transfer complexes of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorodicyanoquinone, picric acid and duraquinone). We also evaluated their thermal and electrochemical properties and we conclude that these complexes are frequency dependent. Charge-transfer complex between thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigma acceptors are more conducting than with pi acceptors.     

Spectroscopic studies on [(DD18C6H2)(HPA)2](PA)2 and [(DD18C6H2)(DDQ)2](DDQH)2 formed in the reaction of N,N'-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane with HPA and DDQ

The interaction of the mixed oxygen-nitrogen cyclic base, N,N'-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (DD18C6) with pi-acceptors such as picric acid (HPA) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) has been studied spectrophotometrically in chloroform at 25 degrees C. The results obtained indicate the formation of 1:4 charge-transfer complexes with the general formula (DD18C6)(acceptor)4. The electronic and infrared spectra of charge-transfer complexes along with the (1)H NMR spectra were recorded and discussed. Based on the data obtained, the complexes were formulated as [(DD18C6H2)(HPA)2](PA)2 and [(DD18C6H2)(DDQ)2](DDQH)2. A general mechanism explaining the formation of the DDQ complex has been suggested.     

Charge-transfer complexes of phenylephrine with nitrobenzene derivatives

The molecular charge-transfer complexes of phenylephrine with picric acid and m-dinitrobenzene have been studied and investigated by IR, 1H NMR electronic spectra in organic solvents and buffer solutions, respectively. Simple and selective methods are proposed for the determination of phenylephrine hydrochloride in bulk form and in tablets. The two methods are based on the formation of charge-transfer complexes between drug base as a n-donor (D) and picric acid, m-dinitrobenzene as pi-acceptor (A). The products exhibit absorption maxima at 497 and 560 nm in acetonitrile for picric acid and m-dinitrobenzene, respectively. The coloured product exhibits an absorption maximum at 650 nm in dioxane. The sensitive kinetic methods for the determination phynylephrine hydrochloride are described. The method is based upon a kinetic investigation of the oxidation reaction of the drug with alkaline potassium permanganate at room temperature for a fixed time at 20 min.     

Charge-transfer derivatization in fast-atom-bombardment mass spectrometry

The formation of charge-transfer complexes as derivatization reactions for fast-atom- bombardment (f.a.b.) mass spectrometry has been investigated. The donor N,N,N′,N′- tetramethyl-1,4-phenylenediamine (TMPD) and the acceptor 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) were studied. The f.a.b, spectrum of this complex in glycerol first yielded the cation radical, TMPD⁺ at m/z 164. However, with time the dominant ion becomes (TMPD+H)⁺. Results suggest that although a strong charge-transfer complex is formed, protonation of the donor molecule occurs whenever possible. In dimethylsulfoxide, initial f.a.b, spectra contain (TMPD+H)⁺, but as solvent evaporates, this ion is supplanted by the cation radical. Increased abundances of the cation radicals for charge- transfer complexes are observed in the absence of solvent or with the use of aprotic solvents. Characteristic ultraviolet/visible spectra of charge-transfer complexes clarify the competing processes of electron and proton transfer, and their time dependence. Charge- transfer derivatization is used to increase signals for the donor cation radicals of anthracene/picric acid, pyrene/picric acid, and indole/trinitrofluorenone.     

Infrared,Raman, 1H NMR,TG, and SEM properties of the charge-transfer interactions between tris(hydroxymethyl)methane with the acceptors picric acid,chloranilic acid,and 1,3-dinitrobenzene

Intermolecular charge-transfer complexes (CT) between the tris(hydroxymethyl)methane (THM) as a donor and picric acid (PA), chloranilic acid (CLA) and 1,3-dinitrobenzene (DNB) as a π-acceptor have been structurally, thermally and morphologically studied in methanol at room temperature. Based on elemental analyses (CHN), the stoichiometry of the obtained CT complexes (THM: acceptor molar ratios) was determined to be 1 : 1 for all three complexes. The CT complexes have been characterized via elemental analyses (CHN), IR, Raman and 1H NMR spectroscopy in order to predict the position of the CT interaction between the donating and accepting sites. Thermal decomposition behavior of these complexes was also investigated, and their kinetic thermodynamic parameters were calculated with Coats-Redfern and Horowitz-Metzger methods. Finally, the microstructure properties of these complexes were observed using scanning electron microscope (SEM).     

In situ synthesis, photometric and spectroscopic studies of chelating system during the 1,4,7,10,13,16-hexaoxacyclooctadecane charge transfer reaction with different acceptors

Electron donor acceptor complexes (EDA) of the 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) as a rich donor were spectrophotometrically discussed and synthesized in solid form according the interactions with different nine of usual π-acceptors like 2,3,5,6-tetrachlorocyclohexa-2,5-diene-1,4-dione (p-chloranil; p-CHL), tetrachloro-1,2-benzoquinone (o-chloranil; o-CHL), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetracyanoquinodimethane (TCNQ), 2,6-dichloroquinone-4-chloroimide (DCQ), 2,6-dibromoquinone-4-chloroimide (DBQ), 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid; CLA), N-bromosuccinimide (NBS), 2,4,6-trinitrophenol (picric acid; PA). Spectroscopic and physical data such as formation constant (K(CT)), molar extinction coefficient (?(CT)), standard free energy (ΔG°), oscillator strength (f), transition dipole moment (μ), resonance energy (R(N)) and ionization potential (I(p)) were estimated in chloroform or methanol at 25°C. Based on the elemental analysis and photometric titrations the CT-complexes were formed indicated the formation of 1:1 charge-transfer complexes for the o-CHL, TCNQ, DCQ, DBQ and NBS acceptors but 1:3 ratio for p-CHL, DDQ, CLA and PA, respectively. The charge-transfer interactions were interpretative according to the formation of dative ion pairs [18C6(?+), A(?-)], where A is acceptor. All of the resulting charge transfer complexes were isolated in amorphous form and the complexes formations on IR and (1)H NMR spectra were discussed.     

Spectroscopic characterization of charge-transfer complexes of morpholine with chloranilic and picric acids in organic media: Crystal structure of bis(morpholinium 2,4,6-trinitrocyclohexanolate)

Electron donor–acceptor interaction of morpholine (morp) with chloranilic acid (cla) and picric acid (pa) as π-acceptors was investigated spectrophotometrically and found to form stable charge-transfer (CT) complexes (n–π*) of [(Hmorp)₂(cla)] and [(Hmorp)(pa)]₂. The donor site involved in CT interaction is morpholine nitrogen. These complexes are easily synthesized from the reaction of morp with cla and pa within MeOH and CHCl₃ solvents, respectively. ¹HNMR, IR, elemental analyses, and UV–vis techniques characterize the two morpholinium charge-transfer complexes. Benesi–Hildebrand and its modification methods were applied to the determination of association constant (K), molar extinction coefficient (?). The X-ray crystal structure was carried out for the interpretation the predict structure of the [(Hmorp)(pa)]₂ complex.     

Deuterium isotope effect on charge-transfer fluorescence

Quantum yields and decay times of fluorescence of charge-transfer complexes of tetracyanoethylene (an electron acceptor) with protonated and deuterated aromatic hydrocarbon donors were measured. The deuterium isotope effect on radiationless transition (identified as the

internal conversion) was observed. This observation is taken as evidence of the dominant role of intramolecular within the donor and/or the acceptor molecule) vibrations in radiationless transitions from excited charge-transfer states of molecular complexes.     

Localized excited triplet states in mixed charge-transfer single crystals: formation of excited multicomplexes

Single crystals of charge-transfer (CT) complexes between tetracyanobenzene as acceptor and different aromatic donors were doped with guest donors. The molecular arrangements of the guest CT complexes forming triple energy traps in the host crystal were determined from the triplet ESR spectra of the traps. A method for the determination of relative charge-transfer triplet energies is proposed. Extended electron delocalization over more than one donor-acceptor pair has been found.     

Quick and simple formation of different nanosized charge-transfer complexes of the antibiotic drug moxifloxacin: An efficient way to remove and utilize discarded antibiotics

A quick and simple procedure for the synthesis of nanosized complexes of the drug moxifloxacin (MOX) is described. MOX nanoparticles were synthesized via charge-transfer (CT) interactions with the organic acceptors picric acid (PA), chloranilic acid (CLA) and chloranil (CHL). The structure and morphology of these nanoparticles were fully characterized using physicochemical techniques, such as UV–visible, IR, ¹H NMR and ¹³C NMR spectroscopies, XRD, SEM, TEM, and elemental and thermal analyses. Notably, it has been found that the complexation of MOX with an organic acceptor leads to well-organized nanoparticles with a main diameter in the range of 10–20 nm. Interestingly, the direct carbonization of the complex containing the PA acceptor leads to nanoporous carbon material with uniform morphology. This method is an efficient way to remove and utilize discarded MOX antibiotic in other products.     

Charge-transfer complex formation between o-chloranil and a series of polynuclear aromatic hydrocarbons

The equilibrium constants, enthalpies and entropies of formation of molecular electron donor-acceptor (EDA) complexes of o-chloranil with a series of aromatic hydrocarbons have been determined spectrophotometrically. Spectroscopic and thermodynamic aspects of these complexes have been analysed.     

Fmoc-protected amino acids as luminescent and circularly polarized luminescence materials based on charge transfer interaction

Fluorenylmethyloxycarbonyl (Fmoc)-protected amino acids are effective building blocks in self-assembled architectures at hierarchical levels, which however show limited luminescent properties and chiroptical activities. Here we introduce a charge-transfer strategy to build two-component luminescent materials with emerged circularly polarized luminescence properties. A library of Fmoc-amino acids was built, which selectively form charge-transfer complexes with the electron-deficient acceptor. Embedding in amorphous polymer matrix or physical grinding could trigger the charge-transfer luminescence with adjusted wavelengths in a general manner. X-ray diffraction results suggest the multiple binding modes between donor and acceptor. And, the solution-processed coassembly could selectively exhibit circularly polarized luminescence with high dissymmetry g-factors. This work illustrates a noncovalent charge-transfer strategy to construct luminescent and chiroptical organic composites based on the easy-accessible and economic chiral N-terminal aromatic amino acids.     

Novel charge-transfer complexes of 4-hexylamino-1,8-naphthalimide-labelled PAMAM dendrimer with some acceptors: a spectrophotometric study

Poly(amidoamine) dendrimers are very interesting macromolecules with highly branched structures and globular-shaped branched polymeric architectures. They are widely used for drug and gene delivery applications. In order to provide important insight into the interactions of poly(amidoamine) dendrimers with some organic acceptors, the binding of small molecules to 4-hexylamino-1,8-naphthalimide-labelled PAMAM dendrimer (PD) have been studied by spectrophotomeric method. The acceptors used in this research include chloranilic acid (CLA), p-chloranil (CHL), 2,6-dichloroquinone-4-chloroimide (DCQ), 2,6-dibromoquinone-4-chloroimide (DBQ), 7,7?,8,8?-tetracyanoquinodimethane (TCNQ), picric acid (PA), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and iodine monobromide (IBr). The spectrophotometric measurements proved that all the charge-transfer (CT) complexes are formed via a stoichiometry (PD: acceptor) of 1:2 (except for IBr acceptor). Accordingly the obtained complexes could be formulated as [(PD)(CLA)₂], [(PD)(DCQ)₂], [(PD)(DBQ)₂], [(PD)(TCNQ)₂], [(PD)(PA)₂], [(PD)(CHL)₂], [(PD)(DDQ)₂] and [(PD)(IBr)₄]. Benesi–Hildebrand and its modification methods were applied to estimate the spectroscopic and physical data.     

Intermolecular charge-transfer complexes between chlorothiazide antihypertensive drug against iodine sigma and picric acid pi acceptors: DFT and molecular docking interaction study with Covid-19 protease

The interaction of chlorothiazide (CH) as donor (D) with picric acid (PA) and iodine (I₂) as π- and σ-acceptors (A), respectively, gives charge-transfer (CT) complexes as a final products. The reaction of donor and acceptors were studied spectrophotometrically. The complexes are generally of the n-π* and n-σ* types, with the ground state wave function primarily characterized by the non-bonding structure. For the micro determination of chlorothiazide using picric acid and iodine as acceptors, the ideal conditions encouraging the formation of complexes are thoroughly explored. It was discovered that the stoichiometry of the molecular structure is 1:1 (D:A). The equilibrium constant and the molar extinction coefficient were calculated using Benesi-Hildebrand and its modifications. DFT/TD-DFT calculations with B3LYP/LanL2DZ and 6-311G++ level of theory were used to provide comparable theoretical data along with electronic energy gap of HOMO→LUMO. Molecular docking calculations have been performed between CT complexes and Covid-19 protease (6LU7) to study the interaction between them and their inhibitory effect.     

Positron annihilation studies of some charge transfer molecular complexes

Positron annihilation lifetimes were measured for some solid charge transfer (CT) molecular complexes of quinoline compounds (2,6-dimethylquinoline, 6-methoxyquinoline, quinoline, 6-methylquinoline, 3-bromoquinoline and 2-chloro-4-methylquinoline) as electron donor and picric acid as an electron acceptor. The infrared spectra (IR) of the solid complexes clearly indicated the formation of the hydrogen-bonding CT-complexes.

The annihilation spectra were analyzed into two lifetime components using PATFIT program. The values of the average and bulk lifetimes divide the complexes into two groups according to the non-bonding ionization potential of the donor (electron donating power) and the molecular weight of the complexes. Also, it is found that the ionization potential of the donors and molecular weight of the complexes have a conspicuous effect on the average and bulk lifetime values. The bulk lifetime values of the complexes are consistent with the formation of stable hydrogen-bonding CT-complexes as inferred from the IR-spectral data.     

π-π Molecular complexes with nitrones,II. Complexation between heterocyclic nitrones and tetracyanoethylene as well as 1,4-benzoquinones

Characteristic charge-transfer absorption bands of some heterocyclic nitrones as electron donor with tetracyanoethylene, 2,3-dichloro-5,6-dicyanobenzoquinone and chloranil as electron acceptor have been measured in methylene chloride solution. The stoichiometry, apparent formation constants and transition energies of the charge-transfer complexes formed as well as the effect of solvent and the stability of these complexes are discussed.     

Polymerization of 2-naphthyl methacrylate in the presence of electron acceptors

The polymerization of 2-naphthyl methacrylate (NM) in toluene in the presence of tetracyanoethylene and picric acid was studied dilatometrically. The overall activation energy for the polymerization was calculated both in the absence and in the presence of electron acceptors. The results (13-7 kcal/ mole for pure NM; 15-1 kcal/mole for NM in the presence of picric acid; 212 kcal/mole for NM in the presence of tetracyanoethylene) show that the influence of the electron acceptor increases with its electron affinity. To explain the kinetics, it was assumed that donor-acceptor interaction of the additives occurs not only with the aromatic ring in the monomer but also with the growing radicals.     

Pulsradiolyse organischer Halogenverbindungen I. Nachweis kurzlebiger Charge-Transfer Komplexe mit Chloratomen

In a solution of benzene in carbon tetrachloride a transient absorption in the visible part of the spectrum could be detected. It appears within less than 0.3 μs after the irradiation by a high-energy electron pulse, and it can be shown to be due to the charge-transfer complex between the chlorine atoms as electron acceptors and benzene molecules as electron donors. A variety of aromatic hydrocarbons also yield similar absorption bands in the visible. They show a linear correlation between the absorption energy and the ionisation potential of the aromatic molecules, which is typical for charge-transfer complexes. A minimum value for the equilibrium constant of complex formation is given. The equilibrium is almost fully shifted to the complex side. An estimated G value for the charge-transfer complex indicates that the complex is actually part of a main reaction in the radiation-induced mechanism. The decay of the charge-transfer complex is mostly pseudo-first order with a half life of a few microseconds.