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.     

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.     

Charge-transfer interactions between piperidine as donor with different σ- and π-acceptors: Synthesis and spectroscopic characterization

Charge-transfer (CT) complexes formed between piperidine (Pip) as donor with monoiodobromide (IBr), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,6-dichloroquinone-4-chloroimide (DCQ), and 2,6-dibromoquinone-4-chloroimide (DBQ), as acceptors have been studied spectrophotometrically. The synthesis and characterization of piperidine CT-complexes of monoiodobromide, [(Pip)(IBr)], 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, [(Pip)(DDQ)], 2,6-dichloroquinone-4-chloroimide, [(Pip)(DCQ)] and 2,6-dibromoquinone-4-chloroimide, [(Pip)(DBQ)] were described. These complexes are readily prepared from the reaction of Pip with IBr, DDQ, DCQ and DBQ within CHCl₃ solvent. IR, UV–Vis techniques and elemental analyses (CHN), characterize the four piperidine charge-transfer complexes. Benesi–Hildebrand and its modification methods were applied to the determination of association constant (K), molar extinction coefficient (?).     

XPS studies of charge transfer interactions in some polyphenylacetylene-electron acceptor systems

X-ray photoelectron spectroscopy (XPS) studies have been performed on charge transfer complexes of trans-polyphenylacetylene (PPA). The acceptors used included halogens, such as I₂ and Br₂, and organic electron acceptors, such as 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), chloranil, fluoranil, and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ). Incomplete and relatively weak charge transfer interactions were observed in most of the complexes. These help to account for the relatively low conductivity levels observed in most of the PPA complexes when compared with the corresponding complexes of other conjugated polymers. PPA has also been found to interact with molecular oxygen to some extent in solution. In complexes involving O₂, Br₂, and fluoranil, XPS data suggest that the charge transfer interaction may have proceeded further than the pure formation of molecular charge transfer complexes.     

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 interactions in some poly[[o-(trimethylsilyl)phenyl] acetylene]-acceptor complexes

Charge transfer (CT) interactions between poly[[o-(trimethylsilyl)phenyl]acetylene] or poly(o-Me₃SiPA) and some electron acceptors were studied by ultraviolet-visible and infrared absorption spectroscopy and by x-ray photoelectron spectroscopy, (XPS). The electron acceptors used included iodine, bromine, o-chloranil, o-bromanil, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and tetracyanoethylene (TCNE). Varying degrees of CT interactions were observed in all of the polymer/acceptor complexes studied. The electrical conductivities σ of the organic acceptor complexes exhibited a strong acceptor concentration dependence at low acceptor levels, with the DDQ complex exhibiting the highest σ. The extent of CT and the redistribution of charges resulting from the CT in all the complexes were revealed by XPS. The poly (o-Me₃SiPA)/I₂ complex film lost iodine spontaneously while more than half of the bromine in the poly (o-Me₃SiPA)/Br₂ complex existed as covalently bonded bromine, even at low halogen loading.     

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.     

DC electrical conduction and morphological behavior of counter anion‐governed genesis of electrochemically synthesized polypyrrole films

Highly conducting polypyrrole (PPY) films, doped with various anions [pTS^?, ClO₄^?, and NO₃^? and mixed electrolyte system (pTS^? + ClO₄^?)], have been electrochemically synthesized in aqueous solution at ～275 K in an inert atmosphere. PPY exhibits metallic order dc conductivity at room temperature and shows variation of conductivity with respect to time of polymerization. Effect of dopant anion on growth mechanism of PPY is evident from its surface morphology. X‐ray photoelectron spectroscopy (XPS), used to examine the surface composition and doping level of various PPY films, confirms the anionic doping into the polymer backbone. Both XPS and ultraviolet–visible spectroscopy give evidence of formation of polarons and bipolarons. The temperature (4.2–320 K)‐dependent dc conductivity data of these PPY films have been explained by Mott's 3D variable‐range hopping conduction model. Mott's parameters have been estimated, and structural disorder with doping is correlated for all the samples. Mott's criterion for distant hopping sites prevails in case of moderately doped samples (PPY3, PPY4, and PPY5), whereas the hopping to nearest neighbor sites is found more suitable in case of highly doped samples (PPY1 and PPY2). The origin of these changes is due to the modification in the molecular structure of PPY, which is governed by different growth mechanisms for organic (pTS^?) and inorganic (ClO₄^? and NO₃^?) counter anions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Alternating copolymerization of 2,3-dichloro-5,6-dicyano-p-benzoquinone with styrene and polymerization behavior with vinyloxy compounds

2,3-Dichloro-5,6-dicyano-p-benzoquinone (DDQ) was found to copolymerize alternatingly with styrene (St). DDQ–isobutyl vinyl ether and DDQ–2-chloroethyl vinyl ether systems gave homopolymers of vinyl ethers, while DDQ–phenyl vinyl ether and DDQ–vinyl acetate systems gave oligomers containing both monomer units. In the terpolymerization of DDQ, p-chloranil (pCA), and St, terpolymers obtained were found to have about 50 mole % of St units regardless of monomer feed ratio and DDQ was incorporated much more rapidly into the terpolymer than pCA. The difference in the reactivity of the acceptor monomers could be attributed to that in their electron-accepting character.     

Relationship between the energy of donor–acceptor bond and the reorganization energy in molecular complexes

Donor–acceptor complexes of silicon halides with ammonia, pyridine, and 2,2′bipyridine SiX₄ · nD (X = F, Cl, Br) have been studied at the B3LYP/pVDZ level of theory. Energies of the donor–acceptor bond have been estimated taking into account the reorganization energy of the donor and acceptor fragments and basis set superposition error correction. Despite of the very low (or even negative) dissociation energy of SiX₄ · nD into free fragments, the Si–N bonding in all complexes is rather strong (75–220 kJ mol^?1). It is the reorganization energy of the acceptor SiX₄ (75–280 kJ mol^?1) that governs the dissociation energy of the complex. Thus, in contrast to the complexes of group 13 halides, the reorganization effects are crucial for the complexes of group 14 halides, and their neglecting leads to erroneous conclusions about the strength of the donor–acceptor bond in these systems. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Oxidation of styrene by 2,3-dichloro-5,6-dicyano-p-benzoquinone

Styrene is oxidized by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), affording hydroquinone mono(2-phenylethyl) ether. Kinetic studies (50°C in CHCl₃) show that the reaction is faster under N₂ than under air and takes placevia intramolecular H-atom transfer within the 1:1 and 1:2 DDQ-styrene charge-transfer complexes. The semiquinone radical intermediate is reoxidized to DDQ by O₂ when the latter is present, therefore, the apparent rate of DDQ reduction is lower. Stability constants of the CT-complexes and kinetic parameters for the oxidation are reported.     

Study on a single flow acid Cd–chloranil battery

This paper describes a novel redox flow battery–single flow acid Cd–chloranil battery. The electrolyte of this battery for both negative electrode and positive electrode is the aqueous intermixture of H₂SO₄–(NH₄)₂SO₄–CdSO₄, the negative electrode is inert metal such as copper foil, and the positive electrode is an insoluble organic material, tetrachloro-p-benzoquinone (chloranil). Typically, the electrolyte is continuously circulated to pass though the cells by means of a single pump as the battery is on duty. There is no requirement for a membrane. Tetrachloro-p-benzo-hydroquinone is oxidized to chloranil at positive electrode and the cadmium ions is reduced to cadmium and electroplated onto the negative electrode during charge. The reverse occurs during discharge. Results obtained with a small laboratory cell show that high efficiencies can be achieved with an average coulombic efficiency of 99% and energy efficiency of 82% over 100 cycles at the current density of 10 mA cm^?2.     

Synthesis,spectroscopic and thermal structural investigations of the charge-transfer complexes formed in the reaction of 1-methylpiperidine with σ- and π-acceptors

The reactions of the electron donor 1-methylpiperidine (1MP) with the π-acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil = CHL) and iodine (I₂) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge-transfer (CT) complexes were recorded. The obtained results showed that the stoichiometries of the reactions are not fixed and depend on the nature of the acceptor. Based on the obtained data, the formed charge-transfer complexes were formulated as [(1MP)(TCNE)₂], [(1MP)(DDQ)]·H₂O, [(1MP)(CHL)] and [(1MP)I]I₃, while in the case of 1MP–TCNQ reaction, a short-lived CT complex is formed followed by rapid N-substitution by TCNQ forming the final reaction products 7,7,8-tricyano-8-piperidinylquinodimethane (TCPQDM). The five solids products were isolated and have been characterized by electronic spectra, infrared spectra, elemental analysis and thermal analysis.     

Polymerization of ethylene in the presence of bis(phenoxyimine) complexes of titanium chloride that contain various substituents in a phenoxy group

The kinetic features of ethylene polymerization with six methylaluminoxane-activated bis(phenoxyimine) complexes of titanium chloride that are distinguished by the electronic properties of substituents in the phenoxy group are studied in the temperature range 30–80°C and at an ethylene pressure of 0.3 MPa. It is shown that, in the presence of an electro-donor or electron-acceptor substituent in the phenoxy group, the catalytic systems under study exhibit high activity (up to ～700 t_PE mol _cat ^?1 mol _ethylene ^?1 h^?1) and form high-molecular-mass PE samples (M _η = (500–900) × 10³) with different molecular-mass distributions. In the case of titanium bis(phenoxyimine) complexes containing donor substituents at the para position of the phenoxy group, the polymerization of ethylene follows the living-chain mechanism, while the introduction of acceptor substituents diminishes the contribution of this mechanism to the reaction.     

Rate of complex formation for poly-n-vinyl carbazole and n-ethyl carbazole with various electron acceptors

The rates of complex formation for poly-N-vinyl carbazole and its saturated monomer analogue, N-ethyl carbazole, with various electron acceptors (chloranil, trinitrobenzene and picric acid) have been investigated. In mole ratios 1:1, the complex forming reactions in chloroform proceed rapidly, as measured by a “stopped flow” method; the rate constants are of the order of 10³ 1. mole^?1 sec^?1. The rate constants are smaller than those of the complexes with tetracyanoethylene as acceptor and decrease with decreasing electron affinity of the acceptor. The rate constants also depend on the molecular weight of the donor.     

Ruthenium(II)–Polyimine–Coumarin Light‐Harvesting Molecular Arrays: Design Rationale and Application for Triplet–Triplet‐Annihilation‐Based Upconversion

Ru^II–bis‐pyridine complexes typically absorb below 450 nm in the UV spectrum and their molar extinction coefficients are only moderate (ε<16 000 M ^?1 cm^?1). Thus, Ru^II–polyimine complexes that show intense visible‐light absorptions are of great interest. However, no effective light‐harvesting ruthenium(II)/organic chromophore arrays have been reported. Herein, we report the first visible‐light‐harvesting Ru^II–coumarin arrays, which absorb at 475 nm (ε up to 63 300 M ^?1 cm^?1, 4‐fold higher than typical Ru^II–polyimine complexes). The donor excited state in these arrays is efficiently converted into an acceptor excited state (i.e., efficient energy‐transfer) without losses in the phosphorescence quantum yield of the acceptor. Based on steady‐state and time‐resolved spectroscopy and DFT calculations, we proposed a general rule for the design of Ru^II–polypyridine–chromophore light‐harvesting arrays, which states that the ¹IL energy level of the ligand must be close to the respective energy level of the metal‐to‐ligand charge‐transfer (M LCT) states. Lower energy levels of ¹IL/³IL than the corresponding ¹M LCT/³M LCT states frustrate the cascade energy‐transfer process and, as a result, the harvested light energy cannot be efficiently transferred to the acceptor. We have also demonstrated that the light‐harvesting effect can be used to improve the upconversion quantum yield to 15.2 % (with 9,10‐diphenylanthracene as a triplet‐acceptor/annihilator), compared to the parent complex without the coumarin subunit, which showed an upconversion quantum yield of only 0.95 %.     

The effect of organic nitriles on the radiation induced polymerization of styrene

The effect of a range of 10 organic nitriles on the radiation-induced polymerization of styrene was studied. A dose rate of 4.4 rad s^?1 was used. A rate of polymerization of styrene (1.744 mol L^?1 of toluene solution) of 5.0 × 10^?7 mol L^?1 s^?1 was found. With organic nitriles present (styrene:nitrile ratio of 1:0.28) the rate of polymerization increased. Rates in the range of 5.5 × 10^?7 ?5.2 × 10^?6 mol L^?1 s^?1, depending on the nitrile present, were obtained. The polymers were partially characterized and evidence of involvement of each of the nitriles in the polymer chains was revealed. The increase in rate of polymerization has been attributed to the part played by nitrile radicals in the initiation of styrene polymerization. Radical yield values [as G(nitrile radical)] were derived from the relevant rate expressions. Values ranged from 2.7 to 49.5, depending on the particular nitrile. Corresponding values of G(nitrile radical) in the range of 5.1–129.4 were obtained by the manipulation of number-average molar mass data. Values of k_pk_t of approximately 2 × 10^?5 L mol^?1 s^?1 were found. Trommsdorff types of effect are absent from these systems.     

Reactions of poly(methyl methacrylate) radicals with some <Emphasis Type="Italic">p</Emphasis>-quinones in the presence of tri-<Emphasis Type="Italic">n</Emphasis>-butylboron in methyl methacrylate polymerization

The polymerization of methyl methacrylate initiated by dicyclohexyl peroxydicarbonate at 30 °C was studied in the presence of tri-n-butylboron and a series of quinones, namely, p-benzoquinone, chloranil, and 2,5-di-tert-butyl-p-benzoquinone, whose concentration changed from 0.25 to 2.00 mol.%. The initial polymerization rate and molecular weight of poly(methyl methacrylate) depend on the structure and concentration of quinone. The growth radicals react with p-benzoquinone and chloranil predominantly at the C=C bond, while they react at the C=O bond of 2,5-di-tert-butyl-p-benzoquinone. The terminal stable oxygen-centered radicals that formed react with alkylborane, terminating reaction chains and generating alkyl radicals into the bulk. The latter are involved in chain initiation.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2114–2119, October, 2004.     

Achieving branched polyethylene waxes by aryliminocycloocta[b]pyridylnickel precatalysts: Synthesis,characterization, and ethylene polymerization

Cycloocta[b ]pyridin‐10‐one was prepared to form the corresponding imino derivatives, which then reacted with (DME)NiBr₂ to form 10‐aryliminocycloocta[b ]pyridylnickel bromides ( Ni1 – Ni5 ). The new compounds were characterized by means of FT‐IR spectroscopy as well as elemental analysis and the organic ligands were also analyzed by the NMR measurements. Furthermore, the molecular structure of a representative complex Ni3 was determined by the single crystal X‐ray diffraction, indicating the distorted tetrahedral geometry around the nickel atom. Upon the activation with either methylaluminoxane (MAO) or diethylaluminium chloride (Et₂AlCl), the title nickel complexes exhibited high activity in ethylene polymerization and produced polyethylene of low molecular weight (1.43–6.78 kg mol^?1) and low dispersity (1.7–2.4), which suggests a single‐site catalytic system. More importantly, the microstructure of the resultant polyethylene (especially degree of branching) and certain physical properties, such as T _m values, can easily be modulated by selecting the proper substituents within the ligands and adjusting the polymerization conditions. This finding demonstrates that it is plausible to use a single catalyst for synthesizing different types of polyethylene on demand.10‐Aryliminocycloocta[b ]pyridylnickel bromides ( Ni1–Ni5 ), upon activation with either MAO or Et₂AlCl, exhibited high activity towards ethylene polymerization and produced polyethylenes with low molecular weight (1.43–6.78 kg mol^?1) and low dispersity (1.7–2.4). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2601–2610     

The preparation,characterization, and selected charge transfer properties of some anthracene functionalized polyesters

Novel anthracene backboned polyesters were successfully prepared by the melt condensation polymerization of anthracene 9,10-diacetic acid dimethyl ester using titanium (IV) n-butoxide as catalyst. Monomer and polymer structures were identified by a variety of methods. The melt polymerizations were carefully controlled to give low molecular weight polyesters soluble in chloroform. ¹H-NMR was used to determine the degree of polymerization and number-average molecular weight for each of the polyesters. Analysis of the 3-5 ppm spectral region contained the necessary resonances for the interpretation. Spectral results show . Higher molecular weight polymers can also be prepared but chloroform solubility is lost. Thermal studies reveal the T_g of these materials varies from 50–60°C depending upon the aliphatic segment of the polymer. Decomposition temperatures in the range of 400–500°C were observed. Charge transfer complexes of these polymers were also studied. Ultraviolet absorption spectroscopy indicates these polyesters are good electron donating systems. Complexation with tetrachloro-1,4-benzoquinone (chloranil) have absorption maxima at approximately 662 nm. Absorption studies also reveal perturbations do exist in the polymer complexes suggesting the possibility of polymer effects. The emission spectra of these materials also confirms that fact.