TD-DFT Calculation on UV-Vis Spectra of the Complex 8-((Trimethoxysilyl)methylthio)quinoline⋅ZnCl<Subscript>2</Subscript>

The electronic structure and absorption spectra properties of the complex 8-((trimethoxysilyl)methylthio)quinoline⋅ZnCl₂ in the gas phase and in acetonitrile (MeCN) have been investigated by means of DFT/TD-DFT calculations. Calculation results indicate that the broad and weak experimentally observed absorption bands of the complex in MeCN at 335.6 nm originates from spin-forbidden singlet-triplet transitions, but the other experimentally observed absorption bands at 318.5 nm, 310.6 nm and 237.5 nm arise from spin-allowed singlet-singlet transitions. Inclusion of MeCN as solvent leads to dramatic changes in the electronic structures and energy levels of the frontier molecular orbitals of the complex, and hence transition mechanisms of the absorption bands are also changed. For the complex, whether in the gas phase or in MeCN, the metal Zn does not participate in the transitions involved, in the gas phase the calculated lowest-energy absorption band of the complex comes from π→π ^∗ mixed with n→π ^∗ transitions with LLCT (ligand-to-ligand charge transfer) character, while in MeCN, the calculated lowest-energy absorption band is of LLCT/ILCT (intra-ligand charge transfer) character.     

The electronic spectra and structure of palladium(II) molecular complexes and clusters

The electronic absorption spectra of palladium(II) diacetate (PDA) complexes with phosphines and sulfides (D) with the composition Pd(OAc)₂ · 2D (1: 2) contain an intense charge transfer band at λ_max ∼ 300 nm (ɛ ∼ 15 000) and do not absorb in the region of 400 nm. Polynuclear compounds such as PDA trimer [Pd(OAc)₂]₃, trimer complexes with D, and four- and six-membered palladium metallocyclic compounds formed in the interaction of PDA with mercaptans absorb at longer wavelengths. The electronic absorption spectra of all the palladium polynuclear compounds (clusters) contain bands at λ_max ∼ 400 nm (ɛ ∼ 1000). The appearance of these bands in the spectra of palladium clusters is evidence of the formation of chemical bonds between neighboring Pd atoms, although Pd…Pd distances substantially exceed the sum of the covalent radii of palladium atoms.     

π-d-Interaction and the temperature dependent magnetic circular dichroism spectra of low spin Fe(III)-heme compounds

The magnetic circular dichroism (MCD) of metmyoglobin cyanide, ferricytochromec and horseradish peroxidase cyanide were measured in the region 340–800 nm over a range of temperatures from 293 to 15 K. All three species show the temperature dependent MCD (TheC-type effects ∼1/T) in both visibleQ and near UVB bands. While the MCD and absorption inB- region as well as the absorption inQ region are quite similar for all three species the MCD inQ- bands reveal the marked differences, especially at low temperatures. To explain these observations, the theoretical treatment based on our previous model (A. P. Mineyev and Yu. A. Sharonov, 1978, Theoret. Chim. Acta (Berl.)49, 295–307) is proposed. The key point of this consideration is the configuration π-d- interaction which in addition to our previous analysis involves the first excited Fe(III)-ion Kramers doublet and theB-Q-mixing effects. The simultaneous least square fit of MCD and absorption data allows to evaluate the π —d- parameters which appear to be of the order of 10²−10³ cm⁻¹. The role of the π -d- interaction in the forming of hemoprotein spectra are discussed.     

Complexation studies of 3-substituted <Emphasis Type="Italic">β</Emphasis>-diketones with selected d- and f-metal ions

Results of spectroscopic investigations related to complex compositions of 3-substituted derivatives of pentane-2,4-dione (β-diketonate) complexes with chosen d- and f-metal ions are presented. Ligands 3-allylacetylacetone (3all-acac) and 3-benzylacetylacetone (3ben-acac) were prepared and used for the complexation study with Cu(II), Co(II), Nd(III), and Ho(III) metal ions. Based on the absorption spectra of lanthanide ions in their hypersensitive transitions, with the use of computer assisted target factor analysis (CAT) and absorption spectra of the ligands with Cu(II) and Co(II), the verification of complex compositions and the determination of their stability constants were achieved. In case of Nd(III) and Ho(III) complexes with β-diketone ligands, absorption of their maxima were studied in the range of hypersensitive transitions ⁴ I _9/2 → ⁴ F _7/2 + ⁴ S _3/2 (λ _max ∼ 734 nm and 748 nm) for Nd(III) and in the range of 435–465 nm, corresponding to the hypersensitive transition ⁵ G ₆ → ⁵ I ₈ (λ _max ∼ 450 nm), for Ho(III).     

Palladium(II) complexes with 1-allyl-3-(2-pyridyl)thiourea: Synthesis and spectroscopic characterization

New Pd(II) complexes with 1-allyl-3-(2-pyridyl)thiourea (APTU) of the formulas [Pd(C₉H₁₁N₃S)Cl₂] (I) and [Pd(C₉H₁₁N₃S)₂]Cl₂ (II) were obtained and examined by UV-Vis, IR, and 1H NMR spectroscopy. The conditions for the complexation reactions were optimized. The instability constants and molar absorption coefficients of these complexes were calculated. Comparison of the characteristic bands in the UV-Vis and IR spectra of the complexes and free APTU revealed that the ligand in both complexes is coordinated to the metal atom in the thione form in the bidentate chelating mode through the S atom of the thiourea group and the pyridine N atom. In the UV-Vis spectra of the complexes, the charge transfer bands (π → π* Py) and n → π* (C=N_Py), (C=S) experience hypsochromic shifts by 450–470 cm⁻¹ caused by the coordination of APTU to the metal ion, which gives rise to ligand-metal charge-transfer bands (C=N_Py → Pd, n → π* (C=S)) and (SPd). The protons in the 6-, 4-, and 3-positions of the pyridine ring and the thiourea NH proton in the chelate ring are most sensitive to the complexation.     

Investigation of UV spectra of isomeric nitropyrazoles by the semiempirical AM1 (CI) method

The absorption bands in the UV spectra of isomeric nitropyrazoles were assigned by the calculations in the semiempirical AMI (CI) approximation. The long-wave absorption of nitropyrazoles is caused by π→π* and η₀→π* transitions. The charge-transfer band is the most intense. The π→π* transitions undergo a considerable bathochromic shift in the deprotonation. The first ionization potential (PI) of the 4-nitropyrazole anion was estimated from the empirical dependence of the energy of the excited π-state on PI of alkyl-substituted 4-nitropyrazoles. The PI of the 4-nitropyrazole anion is 3 eV lower than that of a neutral molecule. This is evidence for a substantial destabilization of the boundary β-orbital in the heterolytic cleavage of the N−H bond. The analysis of the UV and NMR spectra of 3(5)-nitropyrazole confirms the viewpoint that the 3-nitro tautomer predominates in solution. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 2, pp. 310–314, February, 1997.     

Formation of mono-, bi-, and polyradicals upon reduction of poly(arylenesulfophthalides) by metallic lithium

The reduction of poly(biphenylenesulfophthalide) (1), poly(fluorenylenesulfophthalide) (2), and poly(terphenylenesulfophthalide) (3) by metallic lithium in DMSO was studied using UV-visible and ESR spectroscopies. The reduction of compounds 1 and 2 affords blue diamagnetic color centers with absorption bands at 568 and 350 nm (shoulder) for 1 and at 576 and 360 nm (shoulder) for 2. The color centers were attributed to quinoid structures of the Chichibabin"s hydrocarbon type, being biradicals in the ground singlet state. The spectra of compounds 1 and 2 also exhibit weak absorption bands at 420 nm, which are assigned to monoradicals of the triarylmethyl type. The reduction of compound 3, for which the formation of quinoid structures is energetically unfavorable, leads to polyradicals of the triarylmethyl type with a high content (100%) of unpaired electrons in the main polymer chain. These radicals are characterized by absorption bands at 430 nm (allowed transition) and 638 nm (forbidden transition). The paramagnetic centers in all polymers under study give singlet lines with g = 2.0028 and H 10 Oe in the ESR spectra. The color centers and radicals of the triarylmethyl type observed for the poly(arylenesulfophthalides) under study are assumed to be formed upon the dissociative electron transfer from lithium to the sulfophthalide cycles of the polymeric molecules. The PM3 calculations show a high electron affinity of the sulfophthalide cycle and a higher propensity of the fluorenyl bridge to form quinoid structures than that of the biphenyl bridge.     

Photochemical study of the zinc cis-3-(4-imidazolylphenyl)-1-(pyridin-2-yl)[60]fullereno[1,2-c]pyrrolidine-meso-tetraphenylporphyrinate dyad

Axial coordination of fullerenopyrrolidine bearing the donor imidazolyl group, cis-3-(4-imidazolylphenyl)-1-(pyridin-2-yl)[60]fullereno[1,2-c]pyrrolidine (C₆₀∼Im), with zinc meso-tetraphenylporphyrinate (ZnTPP) in an o-dichlorobenzene solution affords a non-covalently bonded donor-acceptor dyad ZnTPP-C₆₀∼Im. The photochemical behavior of the ZnTPP-C₆₀∼Im complex was studied by fluorescence (excitation at λ = 420 nm) and laser kinetic spectroscopy (excitation at λ = 532 nm, 12 ns). The formation constant of the 1: 1 porphyrin-fullerenopyrrolidine complex determined from quenching of ZnTPP fluorescence assuming static intracomplex quenching is 1.6·104 L mol⁻¹. Absorption spectra of the excited states in the system consisting of ZnTPP and Im∼C₆₀ (ZnTPP/C₆₀∼Im) were measured in solution from 380 to 1000 nm. The quenching constant of the triplet-excited ZnTPP with fullerenopyrrolidine C₆₀∼Im was determined. The results obtained indicate the formation of the triplet exciplex {PL}^* ⇌ {P^δ+…L^δ−} in the ZnTPP/C₆₀∼Im system upon laser photolysis. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1541–1547, September, 2006.     

Theoretical studies on Ru(fppz)2(CO)L (L = N -heterocyclic ligand): Electronic structure, absorption, phosphorescence, and solvatochromism

A series of ruthenium(II) complexes Ru(fppz)₂(CO)L [fppz = 3-trifluoromethyl-5(2-pyridyl)pyrazole; L = pyridine (1), 4-dimethylaminopyridine (2), 4-cyanopyridine (3)] were designed and investigated theoretically to explore their electronic structures, absorption, and emissions as well as the solvatochromism. The singlet ground state and triplet excited state geometries were fully optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ level, respectively. The HOMO of 1–3 is composed of d_yz(Ru) atom and π(fppz). The LUMO of 1 and 2 is dominantly contributed by π*(fppz) orbital, but that of 3 is contribute by π*(L). Absorption and phosphorescence in vacuo, C₆H₁₂, and CH₃CN media were calculated using the TD-DFT level of theory with the PCM model based on the optimized ground and excited state geometries, respectively. The lowest-lying absorption of 1 and 2 at 387 and 391 nm is attributed to {[d_yz(Ru) + π(fppz)] → [π*(fppz)]} transition, but that of 3 at 479 nm is assigned to {[d_yz(Ru) + π(fppz)] → [π*(L)]} transition. The phosphorescence of 1 and 2 at 436 and 438 nm originates from ³{[d_yz(Ru) + π(fppz)] [π*(fppz)]} excited state, while that of 3 at 606 nm is from ³{[d_yz(Ru) + π(fppz)] [π*(L)]} excited state. The calculation results showed that the absorption and emission transition character can be changed from MLCT/ILCT to MLCT/LLCT transition by altering the substituent on the L ligand. The phosphorescence of 1 and 2 does not have solvatochromism, but that of 3 at 606 nm (vacuo), 584 nm (C₆H₁₂), and 541 nm (CH₃CN) is strongly dependent on the solvent polarity, so introducing electron-withdrawing group on ligand L will induce remarkable solvatochromism. Supported by the National Natural Science Foundation of China (Grant Nos. 20573042, 20703015, and 20333050)     

Electrochemical bandgaps of a series of poly-3-<Emphasis Type="Italic">p</Emphasis>-phenylthiophenes

The change of the UV-Vis optical absorption of electropolymerized substituted poly-3-p-X-phenylthiophenes (X = -H, -CH₃, -OCH₃, -COCH₃, -COOC₂H₅, -NO₂) has been followed in situ as a function of applied electrode potential in an electrolyte solution of tetraethylammoniumtetrafluoroborate Et₄NBF₄ in acetonitrile. The UV-Vis spectra show features between 300 and 900 nm similar to those observed with many other polythiophenes having a high degree of conjugation. During stepwise oxidation of the poly-3-p-X-phenylthiophene films, the intensity of the absorption due to the π→π*-transition around 450–566 nm decreases, and a new broad absorption band associated with (bi)polaron states appears around 730–890 nm. On the other hand, during the oxidation (p-doping) of the poly-3-p-X-phenylthiophene films, a blue (hypsochromic) shift is observed for both absorption bands. This is explained by taking into account that a polymer contains a distribution of chain lengths, and the longest polymer chains (the absorption of which occurs at lower energies) start to oxidize at the relatively lowest potentials. The electrochemical bandgaps of poly-3-p-X-phenylthiophenes have been estimated based on results of cyclic voltammetry. Bandgaps obtained this way have been found to be generally higher than optical bandgaps; the actual discrepancy was found to depend on the mode of evaluation. Dedicated to Piero Zanello on the occasion of his 65th birthday in recognition of his numerous contributions to inorganic electrochemistry.

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Synthesis, cyclic voltammetry, and UV–Vis studies of ferrocene-dithiafulvalenes as anticipated electron-donor materials

Abstract  

New ferrocenyl ketones were obtained as precursors of novel π-conjugated ferrocene-dithiafulvalene (Fc-DTF) and π-extended-ferrocenedithia-fulvalenes (π-exFc-DTF) as electron-donor conducting materials from ferrocene by a direct aroylation process using the Friedel–Crafts reaction. Novel Fc-DTF conjugates were synthesized using the Wittig–Horner reaction and their structures were determined. The redox behavior of the ferrocenyl carbonyl compounds Fc-DTF and Fc-π-exDTF was investigated in comparison to the parent ferrocene by means of cyclic voltammetry. A one-electron redox behavior was observed for carbonylferrocenes as one wave potential, while a two-electron process was observed as two oxidation waves for the conjugates. Introduction of electron-withdrawing groups led to increasing E _pa values and decreasing ΔE _p values. The UV–Vis spectra of some compounds were studied in comparison with ferrocene. The absorption spectra showed a red-shift with a slight increase in the absorption intensities.     

Solvent effects on some new meso -aryl substituted octabromoporphyrins

A series of porphyrins with tolyl and naphthyl substituents at themeso positions, their octabromoderivatives (OBP) with Br substituents at β-pyrrole positions are synthesised and characterised by chemical analysis,¹H NMR and electronic spectral studies. It is seen that all the OBPs exhibit pronounced red shifts in both the Soret andQ bands of their electronic spectra compared to their non-brominated form in various polar and nonpolar solvents, the energy difference Δv being in the range 2300–2700 cm₋₁. The high energyB band of naphthyl porphyrins (both brominated and nonbrominated) are found to be more red-shifted than that of tolyl porphyrins, owing to the noticeable mesomeric effect of the naphthyl groups. Detailed spectral studies reveal that while none of the nonbrominated porphyrin show solvent-dependent change in theirB andQ bands, all the OBPs manifest significant shifts depending on the nature of solvents. Solvent-solute interaction can be considered to be of strong dipole-dipole nature for OBPs with polar solvents and of π-π type with aromatic non-polar solvents. In the brominated form we find two categories of porphyrins exhibiting distinctly different absorption phenomena in aromatic solvents. The OBPs havingmeso-groups not shielding the porphyrin π-framework exhibit additional absorption peaks (split Soret peaks and broadened Q bands) in some aromatic solvents. This could be explained in terms of π-π type donor-acceptor (DA) complex formation between such bromoporphyrins (acceptor) and the aromatic solvent molecules (donor) that is not possible for OBPs that have bulkymeso groups that block the approach of aromatic solvent molecules close to the porphyrin framework     

Cyclopalladated complexes of 2-phenylbenzothiazole with 4,4′-bipyridyl

Complexes [Pd(bt)(4,4′-bpy)OOCCH₃], [Pd(bt)NO₃]₂(m-4,4′-bpy), [Pd(bt)(m-4,4′-bpy)]₄(NO₃)₄ (bt⁻ is deprotonated form of 2-phenylbenzothiazole, bpy is 4,4′-bipyridyl) are prepared and characterized by ¹H NMR, electron absorption and emission spectroscopy, as well as by voltammetry. The upfield shift of the signal of proton in the ortho-position to the donor carbon atom of the cyclopalladated ligand in the complexes [(Δδ = −(1.1–1.5) ppm] is assigned to the anisotropic effect of the ring current of the pyridine rings of the 4,4′-bipyridyl moiety, which are orthogonal to the coordination plane. Characteristic longwave absorption bands λ = (387±4) nm and the low-temperature phosphorescence bands λ = (512±3) nm in the complexes are assigned to the chromophore {Pd(bt)} metal complex fragment. The reduction waves in the complexes [E _1/2 = −(1.54±0.04) and E _p = −(1.83±0.03) V] are assigned to the ligand-centered processes of the successive electron transfer to the π* orbitals localized predominantly on the coordinated pyridine components of the 4,4′-bipyridyl moiety.     

Synthesis,cyclic voltammetry,and UV–Vis studies of ferrocene-dithiafulvalenes as anticipated electron-donor materials

Abstract  New ferrocenyl ketones were obtained as precursors of novel π-conjugated ferrocene-dithiafulvalene (Fc-DTF) and π-extended-ferrocenedithia-fulvalenes (π-exFc-DTF) as electron-donor conducting materials from ferrocene by a direct aroylation process using the Friedel–Crafts reaction. Novel Fc-DTF conjugates were synthesized using the Wittig–Horner reaction and their structures were determined. The redox behavior of the ferrocenyl carbonyl compounds Fc-DTF and Fc-π-exDTF was investigated in comparison to the parent ferrocene by means of cyclic voltammetry. A one-electron redox behavior was observed for carbonylferrocenes as one wave potential, while a two-electron process was observed as two oxidation waves for the conjugates. Introduction of electron-withdrawing groups led to increasing E _pa values and decreasing ΔE _p values. The UV–Vis spectra of some compounds were studied in comparison with ferrocene. The absorption spectra showed a red-shift with a slight increase in the absorption intensities. Graphical abstract        

Intensity of bands of the C≡C stretching modes in the IR spectra and conjugation in silylacetylenes

A comparative study of the integrated extinction coefficients (A) of the C≡C stretching bands in the IR spectra of acetylene derivatives Me₃SiC≡CR, HC≡CR, and Me₃CC≡CR was carried out. The resonance interactions of substituents with a triple bond are the main cause of the changes in the values ofA. The total resonance effect of the Me₃Si fragment involves both acceptor (d, π-conjugation) and donor (σ, π-conjugation) components; d, π-conjugation dominates in the silylacetylenes studied. Theσ _R ⁰ resonance constant of the Me₃Si substituent in compounds Me₃SiC≡CR is 0.17±0.02. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 76–80. January 1997.     

Resonant emission of UO<Subscript>2</Subscript>, U<Subscript>3</Subscript>O<Subscript>8</Subscript>, and UO<Subscript>2+<Emphasis Type="Italic">x</Emphasis></Subscript> valence electrons under SR excitation near the O<Subscript>4,5</Subscript>(U) absorption edge

The structure of the resonant electron emission (REE) spectra of UO₂ (REE appears under the excitation with synchrotron radiation near the O_4,5(U) absorption edge at ∼100 eV and ∼110 eV) is studied with regard to the X-ray O_4,5(U) absorption spectrum of UO₂ and a quantitative scheme of molecular orbitals based on the X-ray electron spectroscopy data and the results of a relativistic calculation of the electronic structure of UO₂. The structure of the REE spectra of U₃O₈ and UO_2+x is studied for comparison, and the effect of the uranium chemical environment in oxides on it is found. The appearance of such a structure reflects the processes of excitation and decay involving the U5d and electrons of the outer valence MOs (OVMOs, from 0 to ∼13 eV) and inner valence MOs (IVMOs, from ∼13 eV to ∼35 eV) of the studied oxides. It is noted that REE spectra show the partial density of states of U6p and U5f electrons. Based on the structure of REE spectra, it is revealed that U5f electrons directly participate (without losing the f nature) in the chemical bonding of uranium oxides and are delocalized within CMOs (in the middle of the band), which results in the enhancement of the intensity of the REE spectra of CMO electrons during resonances. The U6d electrons are found to be localized near the bottom of the outer valence band and are observed in the REE spectra of the studied oxides as a characteristic maximum at 10.8 eV. It is confirmed that U6p electrons are effectively involved in the formation of IVMOs, which leads to the appearance of the structure in the region of IVMO electron energies during resonances. This structure depends on the chemical environment of uranium in the considered oxides.     

Photodissociation spectrum of cyanobenzene dimer cation. Absence of intermolecular resonance interaction

Electronic spectra of a homo-molecular dimer cation, (C₆H₅CN)₂ ⁺, are measured by photodissociation spectroscopy in the gas phase. Broad features appeared in the 450–650 nm region are characteristic of π₃ → π_CN transitions of the C₆H₅CN⁺ chromophore. No intense band is observed in the 650–1300 nm region, where other aromatic dimer cations usually show charge resonance bands. Two component molecules of (C₆H₅CN)₂ ⁺ cannot take a parallel sandwich configuration suitable for the resonance interaction, because of geometrical constraints due to other stronger interactions.     

Synthesis and photophysical properties of luminescent mononuclear and dinuclear gold(I) complexes with ethynyl-substituted phenanthrolines

A novel asymmetric dinuclear gold(I) complex with 3,6-diethynylphenanthroline, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, has been synthesized from Au(PPh₃)Cl (PPh₃ = triphenylphosphine) and 3,6-diethynyl-1,10-phenanthroline. The asymmetrical dinuclear gold(I) complex, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, demonstrated a weak phosphorescence assignable to the metal-perturbed ³ π–π* transition in the long wavelength region compared to an intense emission of the symmetrical dinuclear complex with 3,8-diethynylphenanthroline, 3,8-bis{(PPh₃)–Au–C≡C}₂-phen. A similar tendency of phosphorescent bands for the mononuclear gold(I) complexes with 5-ethynylphenanthroline, 5-{(PPh₃)–Au–C≡C}-phen, and 3-ethynylphenanthroline, 3-{(PPh₃)–Au–C≡C}-phen was observed. The absorption bands assignable to the π–π*(C≡Cphen) transition and phosphorescent emission assignable to the metal-perturbed ³ π–π* transition for these four gold(I) complexes were reasonably consistent with the results calculated by DFT and TD-DFT.     

Photochemical Transformation of Colchicine: A Kinetic Study

Spectroscopic methods and theoretical calculations were used to study the photophysical properties of colchicine (1). The characteristic bands of colchicine (1) transitions occurring at ∼245 nm and 350 nm arise from n–π ^* and π–π ^* transitions, and were found to be blue shifted with increasing polarity index of the solvent and red shifted (bathocrhomic) with increasing acidity of the media. Solvent type and polarity were found to affect both the rate constant and photo conversion yield. Excitation of colchicine (1) at 366 nm populates the S1 orbital, from which the photoreaction of colchicine (1) initially produces lumicolchicine directly in its ground state by a concerted disrotatory electrocyclization (i.e., 4π electrocyclization involving the tropolone ring). The acidity of the media affects both rate constants and conversion yield; both of these were inversely proportional to the acid concentration. The presence of acid decreases the photo conversion yield of colchicine (1) from 90% to 40%. The ionic strength affects both the rate constants and the photo conversion yield; rate constants are inversely related to the ionic strength. The photochemistry of colchicine (1) is explained on the basis of the initial formation of a solvation complex in the ground state.     

In situ resonant Raman and ESR spectroelectrochemical study of electrochemically synthesized poly(<Emphasis Type="Italic">p</Emphasis>-phenylenevinylene)

The electrochemical synthesis of poly(p-phenylenevinylene) (PPV) and different modifications in the electronic distribution upon electrochemical p-doping (oxidation) and n-doping (reduction) of this polymer film have been studied in situ by resonance Raman spectroscopy, optical absorption spectroscopy and ESR spectroscopy. The polymer film has been prepared by electrochemical reduction of α,α,α′,α′-tetrabromo-p-xylene in dimethylformamide using tetraethylammonium tetrafluoroborate as the electrolyte salt. During electrochemical polymerization the position and relative intensities of the Raman bands change regularly as the chain length increases and finally converge on values reported for chemically prepared PPV. The Raman spectra for electrochemically polymerized PPV is compared to infrared-active vibration bands for electrochemically n-doped PPV. When the polymer undergoes redox reactions (doping-dedoping), shifts and broadening of Raman bands, compared to neutral PPV, are observed. Interpretation of the Raman spectra and the ESR results led to the conclusion that charge transfer in this system is mainly accomplished by polaron species formed upon doping of the polymer. In this reaction the quinoid structure is formed rather than the benzenoid structure. Electronic Publication