Spectra Of Charge-transfer Complexes Research Articles

Lucas sequence and Fibonacci triads of graphs for analysis of charge transfer spectra of complexes of a series of methylated indoles

Lucas sequence and Fibonacci triads of graphs for analysis of charge transfer spectra of complexes of a series of methylated indoles

Infrared Spectra of Charge Transfer Complexes of Biocytin With Organic Acceptors

The infrared (IR) spectra of the well-known biomolecules called biocytin and their charge transfer complexes with standard organic acceptors such as TCNQ (7,7,8,8-tetracyano-p-quinodimethane), TCNE (tetracyano-p-ethylene), DDQ (2,3- dichloro-5,6-dicyano-p-benzoquinone), chloranil, and iodine have been studied in the present work. The spectrum of biocytin contains a beta density at high frequency and a slightly asymmetric triangular distribution as well as a U-shaped distribution at low frequency, the latter being associated with anisotropic disorder. Weak charge transfer from TCNE and iodine reduces the width of U-shaped distribution and makes the triangular peak more asymmetric. Strong CT interactions with TCNQ and DDQ make the triangular peak in absorption become a Gaussian distribution. The strongest interaction with chloranil leads to oscillations in the density of states with square-root singularities. Toward the high frequency side, the interband transition do occur but with either spin-orbit splitting or exciton-phonon coupling. There is correlated hopping in biocytin-iodine complex.

Infrared spectra of charge transfer complexes of bis(N-H-salicylaldiminato)CuII

The infrared spectra of new charge transfer complexes based on bis(N-H-salicylaldiminato)Cu have been studied. The donor chelate interacts with the standard acceptors like TCNQ, DDQ, chloranil, TCNE, TNF and iodine through charge transfer binding interaction. It is found that all charge transfer complexes are Peicrls semiconductors except TCNE complex. TCNE complex is a Mott or Hubbard semiconductor. The spectra of all the complexes are mainly governed by donor spectrum and not by acceptor spectra as in the purely organic radical-ion salts. TCNE, DDQ and TNF complexes have well developed absorption compared to chloranil, TCNQ and iodine complexes in 1800-3000 cm -1 region. Three absorption envelopes are found in some cases in the infrared range as in the case of strongly correlated electron systems.

Vibrational spectra of charge transfer complexes of lead phthalocyanine

Infrared spectra of six charge transfer complexes of lead phthalocyanine (PbPc), namely, PbPc-I 2, PbPc-TCNQ, PbPc-DDQ, PbPc-chloranil, PbPc-TCNE and PbPc-TNF, where TCNQ=7,7,8,8-tetracyano-1,4-quinodimethane, DDQ=2,3-dichloro-5,6-dicyano- p-benzoquinone, TCNE=tetracyano- p-ethylene and TNF=2,4,5,7-tetranitro-9-fluorenone have been studied in the range of 400–4000 cm −1. The analysis of featureless absorption is carried out for studying transition across the Peierls gap of 0.225 eV. The electronic absorption envelopes at 1500, 1100 and 3400 cm −1 are found to have Gaussian shapes and not the degenerate oscillators, as found in purely organic conductors. There is a pairing of two electrons on phthalocyanine ligand as required in Little's model, and consequently, the electronic absorption envelope is a doublet. Electronic absorption envelope is a doublet showing two peaks at 1500 and 1100 cm −1, indicating a two-electron problem in PbPc. Metal–ligand vibrations between 400 and 700 cm −1 lead to indirect transition between the valence and conduction bands and phonon-mediated coupling between metal chains and the side chains.

Functional Polymers. LVII. Electronic Absorption Spectra of Benzotriazole Derivative/Electron Acceptor Systems

Abstract The electronic absorption spectra of charge-transfer complexes (CTC) of benzotriazole derivatives including 2(2H-hydroxyphenyl)2H-benzotriazole-containing copolymers with various electron acceptors were investigated. While no charge-transfer interaction was observed with weak acceptors, strong acceptors such as trinitrofluorenone and pyromellitic anhydride exhibited an absorption of the contact charge-transfer type with these donors. When the very strong acceptor tetracyanoethylene was used as acceptor, new peaks of a CTC type appeared at longer wavelengths. From the wavelengths of the absorption maxima and the equilibrium constants of the CTC, the electron-donating ability of several related (2(2-hydroxyphenyl)2H-benzotriazole derivatives was estimated as follows: 2(2-Hydroxy-5-methylphenyl)2H-benzotriazole > 2H-benzotriazole > 2(4-hydroxyphenyl)2H-benzotriazole > 2(2-acetoxy-5-methylphenyl)2H-benzotriazole > copolymers containing 2(2-hydroxyphenyl)2H-benzotriazole groups.

Charge transfer complexes in addition reactions of CBr4 to unsaturated compounds initiated by Fe(CO)5 systems

The changes in the electronic absorption spectra of charge transfer complexes (CTC) formed in Fe(CO)5 initiation systems qualitatively correlate with the activity of these systems in the initiated homolytic addition of CBr4, to 1-hexene, methyl acrylate, and vinyltrimethylsilane. The formation of an Fe-(CO)4-olefin π-complex is not observed in the reaction of methyl acrylate with CBr4, while the generation of tribromomethyl radicals occurs in a complex CTC, apparently containing all the reaction components, namely, the addend, monomer, Fe(CO)5, and coinitiator. These data show that the study of CTC of Fe(CO)5 initiation systems may be useful for predicting their activity in homolytic addition and telomerization reactions involving halogen-containing addends.

UV Absorption spectra of charge-transfer complexes of iodine with some derivatives of epoxycyclohexane and of glycidyl ether

UV spectroscopy has been used to study the relative donor power of some derivatives of epoxycyclohexane and of glycidyl ether in the formation of charge-transfer complexes (CTC) with iodine. It is shown that the introduction of a second epoxycyclohexane fragment into the molecule of a substituted 1,2-epoxycyclohexane considerably increases the stability of complexes with molecular iodine, and that the donor power of aromatic derivatives of glycidyl ether considerably exceeds that of their structural analogs, derivatives of anisole.

Electronic absorption spectra of charge transfer complexes derived from ferrocene and functionally substituted tetrahalopropanes

1. Electron-donor groups such as CH3 and Si(CH3)2 in CBr3CH2CHBrR compounds in charge transfer complexes with ferrocene produce a hypsochromic shift of the charge transfer band, while electron-withdrawing groups such as CN, CF3, CO2H and CO2CH3 produce a bathochromic shift. 2. The consecutive replacement of bromine atoms in the CBr3CH2CHBr fragment by hydrogen or going from the CBr3 group to CCl3 leads to a hypsochromic shift of the charge transfer band.

Far-i.r. spectra of charge-transfer complexes between IX (X = Cl, Br) and some pyridine and quinoline bases

Far-i.r. spectra of charge-transfer (CT) complexes of IX (X = Cl, Br) with pyridine, quinoline and their derivatives have been measured in solids. Assignments for the intermolecular NI stretching and the modified IX stretching vibrations are proposed. The force constants for these vibrations have been calculated assuming a linear triatomic model, putting a donor molecule as a point mass. The relationship between the relative decrease in the IX stretching force constants and the p K a values of donor molecules is discussed.

Electronic absorption spectra of charge-transfer complexes based on ferrocene and polyhalohydrocarbons

1. Polyhalohydrocarbons containing CHHal2 and CHal3 groups (Hal=Cl, Br) form with ferrocene charge-transfer complexes (CTC). 2. Polyhalomethanes and polyhalo-2-pentenes show the highest activity in the reaction of complex formation with ferrocene. The compounds with the CBr3 group in CTC have the highest extinction. 3. An elongation of the alkyl chain in the molecule of polyhalogen derivatives and the presence of an additional halogen atom in the γ position with respect to the CHal3 group do not exert any significant influence on their CTC spectra with ferrocene.

Electronic effects of substituents in derivatives of thiophene and furan by electronic spectroscopy of charge transfer complexes

1. The electronic absorption spectra of charge transfer complexes of thiophene and furan derivatives with tetracyanoethylene have been studied and the linear character of the dependence relating the charge transfer frequency with the σ+-constants of the substituents has been shown. 2. Thiophene derivatives with SCH3 substituents display a special dependence of the charge transfer frequency on the σ+-constants, which is explained by an enhancement of the donor properties of the substituent in the CTS. 3. Thiophene and furan derivatives with only acyl type substituents do not conform with the established dependences of the charge transfer frequency on σ+ which apparently is due to a shift of the donor center on complex formation.

Spectrophotometric studies of some charge-transfer complexes of tetracyanoethylene with poly(N-vinyl halogenocarbazoles)

The results and numerical analysis of measurements of absorption spectra of charge-transfer complexes of poly(N-vinyl halogenocarbazoles) with tetracyanoethylene are presented. The absorption bands result from donor–acceptor interaction together with values of equilibrium constants, enthalpy, and oscillators strengths of investigated complexes allowed us to conclude that isomerism of complexing took place. The influence of halogen substituents (mono- and disubstitution) in positions 3 and 6 of the carbazole ring (polymeric donor) on the spectral properties of its complexes was observed.

Charge transfer spectra of complexes with benzoquinonechlorimides as electron acceptors

Charge transfer absorption maxima have been determined for a number of new complexes between substituted quinonechlorimides and π-donors in cyclohexane. Electron affinity value of the acceptors p-benzoquinone(4)-chlorimide (BC), 2-chloro p-benzoquinone(4)-chlorimide (MCBC), 2,6-dichloro p-benzoquinone(4)-chlorimide (DCBC) and 2,3,6-trichloro p-benzoquinone(4)-chlorimide (TCBC) have been determined from these spectra and compared with those of the corresponding quinones. Results on E LVMO values for these acceptors as obtained by semi-empirical MO calculations show the same trend. Factors which determine the electron affinity of a quinonoid are discussed.

Vibrational spectra of charge transfer complexes of pyridines with halogens:

The far infrared spectra of some complexes of pyridines with iodine and bromine have been studied in benzene solution. The infrared intensity of the halogen stretching vibration band has been determined for several complexes with different substituted pyridines. A calculation of transition moments and delocalization moments has been performed and the results are compared with the weight of the dative structure based upon the calculation of the force constants using the frequencies ν X−X and ν N−X . The vibronic contribution to the observed infrared intensity is discussed and a relation between the infrared and the previously determined Raman intensity of ν X−X is examined. A further examination of the difference between iodine and bromine as the acceptor molecule has been included.

Vibrational spectra of charge transfer complexes of pyridines and halogens:

The Raman parameters (frequency, intensity and depolarization ratio) of the ν II band of charge transfer complexes of iodine with several pyridine derivatives have been studied in dichloromethane solution at 296 °K. Complex formation brings about an enhancement of the intensity and depolarization degree, similar to the results which have previously been published for pyridine.bromine complexes. Some differences in the magnitude of the enhancement were observed however and these effects are discussed in terms of the charge transfer theory.

Infrared studies of iodine complexes with several aromatic amines

The infrared spectra of charge transfer complexes formed by iodine with fifteen aromatic amines were recorded in the 3200-̄3600 and 700-̄1400 cm −1 ranges. The frequency shifts of the fundamental symmetric and asymmetric NH2 stretching vibrations that occur as a result of complex formation have been studied in relation to the donor properties of the aromatic amines. The HNH bond angle, the NH stretching force constant, and the “s character” of the hybrid orbitals of the nitrogen atom were calculated from the two shifted frequencies; the characteristic differences between complexed and uncomplexed amines were interpreted in terms of the calculated intermolecular charge transfer. Other spectral changes due to complex formation were: a characteristic decrease of the νCN stretching frequency, as well as some small shifts of the αCH and γCH vibrations: a new band which appeared in several cases in the 800 cm−1 region was assigned to the enhancement of the out-of-plane deformation vibration of the amino group.

Electronic spectra of charge-transfer complexes and hydrogen-bonded complexes. General correlations and differences

Electronic spectra of charge-transfer complexes and hydrogen-bonded complexes. General correlations and differences

Infrared Spectra of Charge Transfer Complexes between I-C[tbnd]N and Pyridine Derivatives. I. - Complexation Constant andvI-CStretching Vibration

Abstract The formation of a charge transfer complex brings about perturbations in the vibrational spectrum of both electron donor and electron acceptor molecules. Changes in band frequency which occur when pyridine bases(1–2), organo phosphoryl compounds(3) or sulfoxides(4) form complexes with I-C[dbnd]N, have been studied. The infrared spectrum of I-C[dbnd]N, the σ acceptor, appears to be perturbed by complex formation: decrease of the frequency and increase of the intensity of the vI-C stretching vibration(4, 6, 7) and in some cases, decrease of the integrated intensity of the vC[dbnd]N stretching vibration(6). However, very little information exists about the stability constants of bases complexed with I-C[dbnd]N owing to the difficulty to observe the C-T band lying in the vacuum ultraviolet(4, 8)

Excitation Spectra of Charge-Transfer Complexes in Molecular Crystals

Excitation Spectra of Charge-Transfer Complexes in Molecular Crystals

Frequency shift in the NQR spectra of charge transfer complexes

In the framework of Mulliken's theory a frequency shift in NQR spectra has been considered. It has been shown that in MO LCAO approximation the frequency shift is proportional to the degree of the charge transfer. For the picrylchloride complexes the linearity of this dependence has been confirmed. It has been shown experimentally that the shift is appreciably affected by steric interactions.