Role Of Charge-transfer Complexes Research Articles

Charge-transfer states in photosynthesis and organic solar cells

Light-induced charge-transfer mechanisms are at the heart of both photosynthesis and photovoltaics. The underlying photophysical mechanisms occurring within photosynthesis and organic photovoltaics in particular show striking similarities. However, they are studied by distinct research communities, often using different terminology. This contribution aims to provide an introductory review and comparison of the light-induced charge-transfer mechanisms occurring in natural photosynthesis and synthetic organic photovoltaics, with a particular focus on the role of so-called charge-transfer complexes characterized by an excited state in which there is charge-transfer from an electron-donating to an electron-accepting molecular entity. From light absorption to fully separated charges, it is important to understand how a charge-transfer complex is excited, forming a charge-transfer state, which can decay to the ground state or provide free charge carries in the case of photovoltaics, or radicals for photochemistry in photosynthetic complexes. Our motivation originates from an ambiguity in the interpretation of charge-transfer states. This review attempts to standardize terminology between both research fields with the general aim of initiating a cross-fertilization between the insights and methodologies of these two worlds regarding the role of charge-transfer complexes, inspiring the cross-disciplinary development of next-generation solar cells. Likewise, we hope to encourage photosynthesis researchers to collaborate with the photovoltaics field, thereby gaining further knowledge of the charge-transfer process in natural light-harvesting systems.

Role of charge-transfer complexes in oxygen quenching of excited states of anthracene derivatives in the gas phase

Oxygen quenching of excited triplet and singlet states of gas-phase anthracene and its derivatives that have similar energies of the lower triplet levels but widely different oxidation potentials (0.44 < Eox < 1.89 V) was studied. Quenching rate constants for singlet (kSO2) and triplet (kTO2) states in addition to the fraction of oxygen-quenched singlet and triplet states qS1(T1O2 were determined from the decay rates, fluorescence intensities, and delayed fluorescence as functions of oxygen pressure. It was found that kSO2 values vary from 2·104 (9,10-dicyanoanthracene) to 1.2·107 sec−1·torr−1 (anthracene, 9-methylanthracene, 2-aminoanthracene) and kSO2 values from 5·102 to 1·105 sec−1·torr−1. The kSO2 values for anthracene, 9-methylanthracene, and 2-aminoanthracene, which have fast rates of interconversion from S1 to T1, are close to the rate constants for gas-kinetic collisions and are independent of the oxidation potentials (Eox). The quenching rate constants kSO2 for the other anthracene derivatives and kTO2 for all studied compounds decrease with increasing free energy of electron transfer ΔGET, which indicates the important role of charge-transfer interactions in the oxygen quenching of singlet S1- and triplet T1 states.

A role of charge-transfer complex with iodine in the modification of coal tar pitch

Iodine introduced into coal tar pitch (CTP) can drastically alter its reology and carbonization behavior. Here, the mechanism of interaction between iodine and CTP has been investigated by using various spectroscopic methods such as 127I-NMR, EPR and FT–IR. It is shown that some iodine molecules infiltrated into the CTP and form charge transfer complexes with the relative large aromatic components of the CTP. Hyperfine sublevel correlation spectroscopy (HYSCORE) revealed the molecular size of cation radicals, which contain more than ten benzene rings, and the location of iodine anion that is incorporated at ca. 0.3 nm from the aromatic cation radicals. The elemental H/C ratio decreased and the viscosity of CTP increased with the density of the charge-transfer complexes, which was also increased by the iodine treatment. These results strongly suggest that dehydrogenative polymerization of CTP occurs during the iodine treatment. The cation radicals in the charge-transfer complexes accelerate the dehydrogenative polymerization and result in a high carbon yield.

The role of charge transfer complexes in the photodegradation of polyolefins

AbstractAddition of HALS‐stabilisers, the cut‐off wavelength of the light source, the temperature and the oxygen pressure have an influence on the UV‐degradation mechanism of polyolefins. All these parameters influences the conversion of oxygen into polymeric carbonyls. The results are explained assuming that the initiation of the UV‐degradation of pololefins is due to substrate‐oxygen charge transfer complexes (CTCs).

Reaction of aromatic N-oxides with dipolarophiles. X. Role of charge-transfer complexes in 1,3-dipolar cycloaddition of pyridine N-oxides to phenyl isocyanate.

In the 1, 3-dipolar cycloaddition reaction of 3-methylpyridine N-oxide with phenyl isocyanate, spectroscopic evidence indicates that phenyl isocyanate forms charge-transfer complexes with both pyridine N-oxide and aromatic solvents such as pyridine. In connection with the charge-transfer complex formation, the solvent effect on the site selectivity was investigated. The most prominent solvent effect was observed in the reaction using 3-methylpyridine as a solvent. The equilibrium constants for the interaction of 3-methylpyridine N-oxide with phenyl isocyanate in several solvents were found to be quite large, indicating that the reaction mixtures favor complex formation. The proton nuclear magnetic resonance (1H-NMR) spectra of the mixtures show a high field shift of the methyl signal of 3-methylpyridine N-oxide due to charge-transfer complexation. Based on these results, the structure and role of the complexes are discussed.

Possible role of charge-transfer complexes in cationic polar cycloaddition

Possible role of charge-transfer complexes in cationic polar cycloaddition

Hydrogen bonding and charge transfer: Interaction of OH radical with rare gas atoms

Hydroxyl radical in solid Ne at 4.2 K is known to rotate freely, vibrationally relax slowly, and have an essentially unperturbed structure. However, the HO structure and dynamics are profoundly affected by solvation in the heavier rare gases Ar, Kr, and Xe. One Ar atom nearest neighbor increases the OH (A 2Σ+) vibrational relaxation rate by a factor of ?103, and A 2Σ+↔X 2Π spectra consistant with a linear–linear transition in hydrogen bonded ArHO are observed. The Ar–HO (A 2Σ+) well depth is D0?675 cm−1 with ωe?203 cm−1 and ωexe?13.1 in solid Ar host; the Kr–HO (A 2Σ+) well depth is ?1000 cm−1. The Ar–HO hydrogen bond length is shorter by Δre=1.15±0.1 Å in the excited state. The OH (A 2Σ+) (0,0) emission band shifts from 3090 in Ne to 4400 Å in Xe. The theory of hydrogen bond formation in both ground and excited states is discussed, with particular reference to the contribution of charge transfer in various environments. Comparison is made with the spectra of hydrogen halides, and the physical origin of rotation–translation coupling theory is discussed. The role of charge transfer complexes in the gas phase quenching of free radical luminescence by rare gas atoms is also considered.

Electronic conduction in bimolecular lipid membranes: exciton mechanism of iodine effect

The effects of iodine, iodide ion and triiodide ion on the electrical conduction of artificial bimolecular lipid membranes are discussed. It is shown that exciton-exciton and exiton-ion interactions may be responsible for the electronic charge carrier generation at the interface. The dramatic resistance drop of bimolecular lipid membranes in the presence of iodine-iodide is attributed to these exciton processes. A detailed description of the elementary steps of the overall reactions postulated earlier is given. Some aspects of the possible role of charge transfer complexes and of electronic properties of membranes in catalytic processes are outlined.

The role of charge-transfer complexes in cyclocopolymerization

Abstract

Iodine photocatalyzed cis ? trans isomerization of 3-styrylpyridine. Role of charge transfer complex

The iodine photocatalyzed cis → trans isomerization of 3-styrylpyridine has been investigated in n-hexane at 25°C by irradiation at 408, and 478 nm where the free and complexed iodine absorb competitively. The mechanism of the free and complexed iodine photocatalysis is the same, the charge-transfer complex with styrylpyridine dissociating to give two iodine atoms with a lower yield (φ478= 0.2) than molecular iodine (φ478= 0.5). Some experiments with stilbene gave similar results. The mechanism is discussed with respect to that reported for stilbene.

Role of charge-transfer complexes in the photooxidation of ethers with oxygen

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRole of charge-transfer complexes in the photooxidation of ethers with oxygenVirgil I. Stenberg, Richard D. Olson, Chiou Tong Wang, and Norman I. KulevskyCite this: J. Org. Chem. 1967, 32, 10, 3227–3229Publication Date (Print):October 1, 1967Publication History Published online1 May 2002Published inissue 1 October 1967https://doi.org/10.1021/jo01285a076RIGHTS & PERMISSIONSArticle Views101Altmetric-Citations43LEARN 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 (448 KB) Get e-Alerts Get e-Alerts

Liquid-phase oxidation of hydrocarbons. Part 4.—Indene and tetralin: occurrence and mechanism of the thermal initiation reaction with oxygen

A study has been made of the possibility of a liquid-phase molecular reaction between oxygen and the hydrocarbons indene and tetralin by fully inhibiting the autoxidation chain. The hydroperoxide-inhibitor reaction AH+ROOH→A˙+RO˙+H2O is believed responsible for the autoacceleration observed. The occurrence of an oxygen+hydrocarbon reaction by a third-order reaction has been reasonably established. This order is consistent with a termolecular process, [graphic omitted] where ki= 2.4 × 105 exp (–23800±1500//RT)mole–2 l.2 sec–1, (tetralin)ki= 3.9 × 103 exp (–18800±1500//RT)mole–2 l.2 sec–1. (indene) The mechanisms of the initiation processes are discussed, and the possible role of charge transfer complexes is considered.