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An in situ spectroelectrochemical study of the oxidation of the μ-oxosilicon phthalocyanine dimer [(SiPc)2O][OSiHx3]2 utilizing cyclic voltammetry, electron spin resonance spectroscopy, and visible–near infrared spectroscopy has been carried out. The results of this study show that oxidation of the dimer yields the paramagnetic radical dimer [(SiPc)2O][OSiHx3]2 + and then the diamagnetic dimer [(SiPc)2O][OSiHx3]22+. The study shows that the rings of [(SiPc)2O][OSiHx3]22+ are antiferromagnetically coupled.

The typical design of chiral electroactive materials involves attaching chiral pendants to an electroactive polyconjugated backbone and generally results in modest chirality manifestations. Discussed herein are electroactive chiral poly-heterocycles, where chirality is not external to the electroactive backbone but inherent to it, and results from a torsion generated by the periodic presence of atropisomeric, conjugatively active biheteroaromatic scaffolds, (3,3′-bithianaphthene). As the stereogenic element coincides with the electroactive one, films of impressive chiroptical activity and outstanding enantiodiscrimination properties are obtained. Moreover, chirality manifestations can be finely and reversibly tuned by the electric potential, as progressive injection of holes forces the two thianaphthene rings to co-planarize to favor delocalization. Such deformations, revealed by CD spectroelectrochemistry, are elastic and reversible, thus suggesting a breathing system.

The in situ spectroelectrochemical and electron spin resonance (ESR) behavior of the recently prepared N,N,N',N'-tetrakis-(4-diphenylamino-phenyl)-thiophene-2,5-diamine 11 is presented. The results are compared to the ones of the parent 2,5-bis-diphenylamino-thiophene 41 as well as to the corresponding high-molar third dendrimer generation 8 containing the same thiophene-2,5-diamine core. The dendritic compound 11 can be reversibly oxidized in three separated steps to yield the corresponding stable monocation 11(•+), dication 11(2+), and tetracation 11(4+). A well resolved ESR spectrum of the corresponding cation radical 11(•+) with dominating splittings from two nitrogen atoms and two hydrogen atoms was observed at the first oxidation peak similar to 41(•+). The shape of the SOMOs orbitals very well correlates with the proposed distribution of the unpaired electron mainly on the thiophene center and neighboring nitrogen atoms. The spin delocalization on the central thiophene moiety in the monocations for all three model compounds 41(•+), 11(•+), and 8(•+) was confirmed. The computed single occupied molecular orbital (SOMO) for trication 11(•3+) is completely different compared to the SOMO of the corresponding monocation 11(•+), and it confirms a largely delocalized unpaired spin density. Dominating diamagnetic product was determined at the third oxidation peak, confirming the formation of a tetracation by a two electron oxidation of ESR silent dication. The positive charge is fully delocalized over the lateral parts of the molecule leading to the high stability of tetracation 11(4+). The estimated theoretical limit energy of the lowest optical transition S0 → S1 is 2.90 eV, and it can be achieved for the 3D dendrimer generation.

The magnetism of DySc(2)N@C(80) endofullerene was studied with X-ray magnetic circular dichroism (XMCD) and a magnetometer with a superconducting quantum interference device (SQUID) down to temperatures of 2 K and in fields up to 7 T. XMCD shows hysteresis of the 4f spin and orbital moment in Dy(III) ions. SQUID magnetometry indicates hysteresis below 6 K, while thermal and nonthermal relaxation is observed. Dilution of DySc(2)N@C(80) samples with C(60) increases the zero-field 4f electron relaxation time at 2 K to several hours.

The electrochemical doping of emeraldine salt and emeraldine bases with different weight average molecular weights was studied by in situ Fourier transform infrared (FTIR) spectroelectrochemistry using attenuated total reflection (ATR) technique. The formation and stabilization of charge carriers in polyaniline during p-doping was followed in dependence of the chain branching. The potential dependence of the IR bands during the oxidation of the polymer clearly demonstrates the formation of the different charged polymer structures (π-dimers, polarons, and bipolarons). It is shown that IR bands usually attributed to a semiquinoid polaron lattice correspond in fact to doubly charged species, π-dimers, which are face-to-face complexes of two polarons. Bands corresponding exclusively to polarons have been identified at 1266, 1033, and 1010 cm(-1), suggesting that polarons are predominantly stabilized on the linear segments near the polymer branches by phenazine.

The structure of emeraldine salt and emeraldine bases with different molar weight and their behavior in electrochemical doping was studied by different spectroscopic and spectroelectrochemical techniques. By Fourier transform infrared (FTIR) spectroscopy, the branching of the polymer chain at tri- and tetrasubstituted benzene rings as well as the presence of small amounts of phenazine units are shown. The branching of the polymer chains increases with the increasing of the molar weight of emeraldines. The optical transitions in protonated and unprotonated emeraldine were studied by ultraviolet-visible near-infrared (UV-vis NIR) spectroscopy. By comparison of the electron spin resonance (ESR) spectra of emeraldine in protic solvents and acidic solutions, the emeraldine bases are shown to be to some extent protonated. Applying in situ ESR-UV-vis NIR spectroelectrochemistry, the charged states in emeraldines upon p-doping were investigated considering the influence of the nonideal "linear" polymer structures. The initial stage of oxidation of the emeraldine base and salt consists of the different charged states. The phenazine units in the polymer chains stabilize the charged states in the emeraldines upon p-doping.

The interaction of single-walled carbon nanotubes (SWCNTs) and α-sexithiophene (6T) was studied by Raman spectroscopy and by in situ Raman spectroelectrochemistry. The encapsulation of 6T in SWCNT and its interaction causes a bleaching of its photoluminescence, and also small shifts of its Raman bands. The Raman features of the SWCNT with embedded 6T (6T-peapods) change in both intensity and frequency compared to those of pristine SWCNT, which is a consequence of a change of the resonant condition. Electrochemical doping demonstrated that the electrode potential applied to the SWCNT wall causes changes in the embedded 6T. The effects of electrochemical charging on the Raman features of pristine SWCNT and 6T@SWCNT were compared. It is shown that the interaction of SWCNT with 6T also changes the electronic structure of SWCNT in its charged state. This change of electronic structure is demonstrated both for semiconducting and metallic tubes.

The role of the chemical structure in an alternative charge stabilisation and a changing reactivity of star-shaped compounds with a central triazine ring linked to aryl groups like thiophene, furan or ethylenedioxythiophene synthesized by a Stille cross-coupling procedure, is followed by spectroelectrochemical measurements. While cathodic reduction leads to stable anion radicals with a delocalised spin on the central triazine moiety, dimerisation and oligomerisation occurs upon anodic oxidation. The stability of the charged states in the polymer film increased substantially using an EDOT (3,4-ethylenedioxythiophene) side group. The location of the charged states on the molecules has been proved by computations. These star-shaped molecules are excellent model structures for studies of the competition of dimerisation and oligomerisation processes based on the variation of the electron and spin distribution in the molecules. Keywords: Star-shaped compounds, ESR/UV–vis–NIR spectroelectrochemistry, Charged states, Central triazine ring

The redox behavior of N,N,N',N'-tetrakis(4-aminophenyl)benzidine (A) and its N,N,N',N'-tetrakis(4-methoxyphenyl)-substituted analogue (B) was studied in detail by a new designed in situ thin layer electron spin resonance (ESR)/UV-vis-NIR spectroelectrohemical cell. The spectroelectrochemical studies of cation radicals, dications, and tetracations indicate a strong difference in stability of higher ions of two model compounds with different phenyl substitution. In cyclovoltammetry the small peak separation of the first two oxidation peaks for both compounds points to a small energetic difference in the first two electron transfers, while the peak separation of the second and third peak is quite large. A well resolved ESR spectrum of the B(*+) cation radical with dominating splittings from two nitrogen atoms is observed and an ESR silent product was determined at the third oxidation peak for both compounds, confirming the formation of a tetracation by a two electron transfer at the third voltammetric peak. In contrast to structure A a more complex redox behavior was found for B under voltammetric cycling. The reaction mechanism indicates the transformation of B in a new product P with a carbazole moiety. This compound can form a highly stabilized cation radical P(*+). A theoretical study based on density functional theory calculations has clarified the role of charging in changes to the structures of both triarylamine derivatives A and B.

Among the applications of fullerene technology in health sciences the expanding field of magnetic resonance imaging (MRI) of molecular processes is most challenging. Here we present the synthesis and application of a Gd(x)Sc(3-x)N@C(80)-BioShuttle-conjugate referred to as Gd-cluster@-BioShuttle, which features high proton relaxation and, in comparison to the commonly used contrast agents, high signal enhancement at very low Gd concentrations. This modularly designed contrast agent represents a new tool for improved monitoring and evaluation of interventions at the gene transcription level. Also, a widespread monitoring to track individual cells is possible, as well as sensing of microenvironments. Furthermore, BioShuttle can also deliver constructs for transfection or active pharmaceutical ingredients, and scaffolding for incorporation with the host's body. Using the Gd-cluster@-BioShuttle as MRI contrast agent allows an improved evaluation of radio- or chemotherapy treated tissues.

The interaction of double wall carbon nanotubes (DWCNTs) and the conducting polymer poly(3,4-ethylenedioxythiphene)/polystyrenesulfonate (PEDOT/PSS) was studied by in-situ Raman spectroelectrochemistry. The mixing of DWCNTs with PEDOT/PSS caused a partial doping of the outer tube of DWCNTs, which was indicated by the relative change of the Raman intensity of the DWCNTs features. On the other hand, the bands corresponding to inner tubes of DWCNTs and to the polymer were almost untouched by assembling both species into a composite. The in-situ Raman spectroelectrochemical experiments have shown that the changes in electronic structure of inner tubes of DWCNTs embedded in PEDOT/PSS matrix are dependent on the doping level. While at the low doping level of the composite, the Raman features of inner tubes of DWCNTs do not change significantly, at high doping level they reflect the changes caused by the applied electrochemical potential similar to those observed in the polymer-free DWCNTs.

A combined spectroelectrochemical study by ESR/UV-vis-NIR as well as FTIR spectroscopy on the influence of the copolymer composition on the stabilization of charges upon electrochemical p-doping is presented. As compared to the parent homopolymers 3-hexylthiophene (3-HeTh) and 3-methylthiophene (3-MeTh) which seems to be irregular, FTIR studies of the copolymer of both monomers (copMeHeTh) point to a regioregular structure. The in situ ESR and UV-vis-NIR spectroelectrochemistry at higher doping levels of the polymeric materials proves bipolarons and polaron pairs as stable charged states in poly(3-hexylthiophene) as well as the copolymer copMeHeTh. During the p-doping of poly(3-methylthiophene) bipolarons are the dominating species at higher doping levels. It is demonstrated that only the simultaneous use of both the ESR and the UV-vis-NIR spectroscopy enables the differentiation of polarons (paramagnetic) and polaron pairs (diamagnetic) in a conducting polymer.

Raman spectroscopy and in situ Raman spectroelectrochemistry have been applied to the study of the lithium vapor doping of C 60 @SWCNTs (peapods; SWCNT = single-walled carbon nanotube). A strong degree of doping was proven by the disappearance of the radial breathing mode (RBM) of the SWCNTs and by the attenuation of the tangential (TG) band intensity by two orders of magnitude. The lithium doping causes a downshift of the A g (2) mode of the intratubular C 60 by 27 cm -1 and changes the resonance condition of the encapsulated fullerene. In contrast to potassium vapor doping, the strong downshift of the TG band was not observed for lithium doping. The peapods treated with lithium vapor remained partially doped even when they were exposed to humid air. This was reflected by a reduction in the intensity of the nanotube and the fullerene modes and by the change in the shape of the RBM band compared with that of the undoped sample. The A g (2) mode of the intratubular fullerene was not resolved after contact of the lithium-doped sample with water. Lithium insertion into the interior of a peapod and its strong interaction with the intratubular fullerene is suggested to be responsible for the air-insensitive residual doping. This residual doping was confirmed by in situ spectroelectrochemical measurements. The TG band of the lithium-doped peapods did not undergo an upshift during the anodic doping, which points to the formation of a stable exohedral metallofullerene peapod.

The redox behavior of Sc 3N@C 68 is studied systematically by means of electrochemistry, in situ ESR/Vis-NIR spectroelectrochemistry, and detailed theoretical treatment. Formation of the negatively and positively charged paramagnetic species for the same trimetallic nitride endohedral fullerene is demonstrated for the first time. The electrochemical study of Sc 3N@C 68 exhibits two electrochemically irreversible but chemically reversible reduction steps and two reversible oxidation steps. A double-square reaction scheme is proposed to explain the observed redox reaction at cathodic potentials involving the reversible dimerisation of the Sc 3N@C 68 monoanion. The spin state of the radical cation and the radical anion is probed by ESR spectroscopy, indicating that in both states, the large part of the unpaired spin is delocalized on the fullerene cage. The charged states of the non-isolated pentagon rule fullerene are characterized furthermore by in situ absorption spectroscopy. The interpretation of experimental data is supported by the density functional theory (DFT) calculations of the spin distribution in the anion and cation radicals of Sc 3N@C 68 and time-dependent DFT calculations of the absorption spectra of the charged species.

It is demonstrated for the C84 fullerene molecule that the in situ ESR spectroelectrochemistry gives a clear insight into the isomeric purity of higher fullerenes and allows the detection of minor impurities whose presence is not found by other spectroscopic techniques. The monoanion of purified D2d C84:23 fullerene isomer was studied by ESR-spectroelectrochemistry in detail, resulting in a relatively broad ESR line because of the high symmetry of the fullerene cage. The minor impurity in the C84 monoanion ESR spectrum, with a sharp line (ΔBpp = 0.15 G) and g = 2.0009 which compose the 2% of the signal was identified as monoanion of the C2 C82:3 isomer. The second impurity in the D2d C84:23 is attributed to the Cs C84:16 isomer which was neither found by NMR spectroscopy nor by cyclic voltammetry. Keywords: In situ ESR spectroelectrochemistry, Cyclic voltammetry, Fullerene isomers, Fulleride anions, C84

The application of in situ ESR–UV/VIS/NIR spectroelectrochemistry to the highly purified C82:3 fullerene isomer with C2 symmetry made the detailed characterization of the radical structures formed by electrochemical generation possible. This first comprehensive spectroelectrochemical study of the stable radical anion and cation of an empty cage higher fullerene in acid-free organic electrolyte is a contribution to the general understanding of charged states at endohedral fullerenes. Keywords: Fullerenes, Fullerene ions, Ion radicals, ESR–UV/VIS/NIR spectroelectrochemistry

The first non-IPR C(76) cage based on a mixed metal nitride cluster, DySc(2)N@C(76), was successfully synthesized and isolated. DySc(2)N@C(76) is a stable fullerene with a small band gap of 0.96 eV. According to the FTIR spectroscopic study in combination with extensive DFT calculations, the cage structure of DySc(2)N@C(76) has been assigned to the non-IPR C(s): 17490-I isomer having two pairs of the adjacent pentagons. DySc(2)N@C(76)provides the first example of stabilization of the non-IPR C(76) cage by encapsulation of an asymmetric DySc(2)N mixed cluster, revealing the role of the cluster structure on the stability of the fullerene cage. As the asymmetric DySc(2)N cluster has a more suitable geometry for the inner space of the C(76) cage compared to that of the homogeneous clusters like Sc(3)N or Dy(3)N, the highest yield for C(76)-based cluster fullerenes with the Dy(x)Sc(3)-(x)N mixed nitride cluster is achieved for the DySc(2)N@C(76)

It is shown for the first time that the most important intermediate formed during aniline polymerization, the p-aminodiphenylamine, forms a pi-dimer under oxidation at room temperature in acidified organic solvents that are used in electropolymerization. N-Phenylquinonediimine, which is generally assumed to be formed under oxidation, is only formed in basic solutions and in ionic liquids. Most of the mechanistic studies reported so far take the formation of N-phenylquinonediimine under consideration, although it is not consistent with the UV-vis spectra measured during oxidation of p-aminodiphenylamine. The formation of a pi-dimer is very well consistent with the electronic spectra of the oxidation product. In this way the pi-dimer is very important for the interpretation of the UV-vis spectra of higher oligomers and polyaniline as well. Furthermore, it offers a new interpretation of the redox behavior of p-aminodiphenylamine as found by cyclic voltammetry and has to be considered in the mechanism of the electrochemical polyaniline formation.

Since the last general reviews in the field of endohedral fullerenes by Shinohara in 2000 and by Akasaka and Nagase in 2002, the variety of endohedral structures has been extended tremendously. With the turn of the millennium the world of endohedral fullerenes has changed in all respects.

Unconventional fullerenes are those smaller than C(60) or those intermediate between C(60) and C(70), which are not stable in structure as none of the unconventional fullerene isomers satisfying the "isolated-pentagon-rule" (IPR). Below we report the synthesis of a stable unconventional fullerene derivative C(64)H(4) by introducing methane in the fullerene productions with the normal Krätschmer-Huffman method. We also applied various spectroscopic measurements such as mass spectrometry, (13)C NMR, IR, UV-vis absorption spectrometry, etc. to characterize the structural and electronic properties of this molecule, revealing an unprecedented fullerene cage with a triplet of directly fused pentagons in the framework of C(64)H(4). Four hydrogen atoms are added to the carbons at vertexes of fused pentagons to allow the bond angles at these sites close to the sp(3) tetrahedral angle, which essentially release the sp(2) bond strains on the abutting-pentagon sites of C(64). Ab initio calculations were performed to explore the electronic property and simulate the (13)C NMR and IR spectra of this fulleride, which reproduced well the experimental results and confirmed the structural assignment of the C(64)H(4).

A new homologous series of alpha,alpha'-bis(diphenylamino)-capped oligothiophenes, prepared by a palladium-catalyzed coupling reaction of stannylated 2-diphenylaminothiophenes with 2-mono- or 2,5-dibromothiophenes and their homologues, was studied by in situ ESR/UV-vis/NIR spectroelectrochemistry. In general, the oxidation potentials of these oligothiophenes were found to be proportional to the inverse number of thiophene units. However, the potential slope of the first oxidation is completely different from that of higher oxidation steps. Trication radicals were identified by electron spin resonance (ESR) for higher thiophene homologues in addition to monocation radicals (polarons). According to the ESR hyperfine structures, the unpaired electron is delocalized in the conjugated system. In contrast to the parent alpha,alpha'-bis(diphenylamino)-capped oligothiophenes, the UV-vis/NIR absorption maxima of the oxidized species strongly depend on the number of thiophene units. Spin-restricted and spin-unrestricted Kohn-Sham density functional calculations were used to explain and to understand these properties. Absorption wavelength and intensities were calculated by the time-dependent density functional response theory. Unrestricted density functional calculations of oligothiophene dications (bipolarons) with five or more thiophene rings result in spin-broken structures which may be considered as two-polaron biradicals (polaron pairs).

Poly(3,4-ethylenedithiathiophene) (PEDTT) is a polythiophene-like conjugated polymer in which each thiophene ring is functionalized with an ethylenedithia bridge. As such, PEDTT is the sulfur analogue of the well-known poly(3,4-ethylenedioxythiophene) (PEDOT). Substituent effects, namely the presence of sulfur atoms in PEDTT replacing the oxygen atoms of PEDOT, do not provide a simple explanation for the different electronic properties of the two polymers in the neutral state. This paper reports the spectroscopic properties of PEDTT, studied by in situ techniques such as IR-, Vis-, and electron spin resonance (ESR) spectroelectrochemistry. The differences observed upon electrochemical oxidation of PEDTT and PEDOT (e.g., the different infrared active vibrational band patterns in IR spectroelectrochemistry as well as the different nature of the charged states) are even more marked than those observed in the neutral state. These results, with AM1 calculations, indicate conformational effects as a possible explanation for the different electronic and spectroscopic properties of PEDTT and PEDOT.

The electronic and vibrational structure of the nitride clusterfullerene Tm3N@C80 (I) was investigated by cyclic voltammetry, FTIR, Raman, and X-ray photoemission spectroscopy. The electrochemical energy gap of Tm3N@C80 (I) is 1.99 V, which is 0.13 V larger than that of Sc3N@C80 (I). FTIR spectroscopy showed that the C80:7 (I(h)) cages in Tm3N@C80 (I), Er3N@C80 (I), Ho3N@C80 (I), Tb3N@C80 (I), Gd3N@C80 (I), and Y3N@C80 (I) have the same bond order. The analysis of low-energy Raman spectra points to two uniform force constants which can be used to describe the interaction between the encaged nitride cluster and the C80:7 (I(h)) cage in M3N@C80 (I) (M = Tm, Er, Ho, Tb, Gd, and Y). Because the M3N-C80 bond strength is strongly dependent on the charge of the metal ions, this is a direct hint for a 3+ formal valence state of the metal ions in these nitride clusterfullerene series, including Tm3N@C80 (I). Photoemission spectra of the Tm 4d core level and the Tm 4f valence electrons provided a direct proof for a (4f)12 electronic configuration of the encapsulated thulium. In conclusion, thulium in Tm3N@C80 (I) has a formal electronic ground state of +3, in contrast to the +2 state found in Tm@C82. It is demonstrated that the valence state of metal atoms encaged in fullerenes can be controlled by the chemical composition of the endohedral fullerene.

The doping level of spin-coated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDT:PSS) films was adjusted quantitatively by an electrochemical doping/dedoping process using p-toluenesulfonic acid in acetonitrile as supporting electrolyte. Higher oxidation states relative to as-prepared layers remain stable under dry condition, and the electrochemical treatment does not affect the surface morphology and homogeneity of the polymer film. The work function of PEDT:PSS increases with the doping level after adjusting the layer at electrode potentials higher than the value of the electrochemical equilibrium potential (E e q ) of as-prepared films. The ohmic behavior for hole-injection is nearly achieved at anode/NPB interfaces for a PEDT:PSS anode with very high doping level (E e q of up to 0.59 V vs Ag/AgCl). This indicates a further reduction of the hole-injection barrier at the contact of polymeric anode/hole transport layers.

[reaction: see text] A series of new 2-amino-5-thienyl-substituted multicharged methinium compounds have been prepared and characterized spectroscopically and electrochemically by reaction of lithiated species of N,N-disubstituted 2-aminothiophenes with alkyl derivatives of di- and tricarbonic acids and subsequent addition of perchloric acid.

Poly(dithienothiophene)s (PDTTs), low band-gap conjugated polymers with polythiophene-like chain where an aromatic thienothiophene moiety is fused to each thiophene ring, were studied using Raman spectroscopy, photoinduced infrared absorption, as well as attenuated total reflection Fourier transform infrared (ATR-FTIR) and electron spin resonance (ESR) spectroelectrochemistry. The spectroelectrochemical studies were performed in situ during p- and n-doping (electrochemical oxidation and reduction, respectively). Raman lines of the pristine polymers are compared to infrared active vibration (IRAV) bands due to the charge carriers injected by the electrochemical doping processes or by illumination. The different π-electron distribution along the polythiophene-like chain, which determines the different band-gap sizes, also account for the different lattice relaxations and vibrational behaviors shown by these polymers. By means of in situ ESR spectroscopy, the formation of paramagnetic positive and negative c...

The low-temperature magnetic properties of the endohedral metallofullerene HoSc2N@C-80 have been studied by superconducting quantum interference device (SQUID) magnetometry. Alternating current (ac) susceptibility measurements reveal that this molecule exhibits slow relaxation of magnetization in a small applied field with timescales in the order of milliseconds. The equilibrium magnetic properties of HoSc2N@C-80 indicate strong magnetic anisotropy. The large differences in magnetization relaxation times between the present compound and the previously investigated DySc2N@C-80 are discussed.

The population of valence-band electronic states of single-walled carbon nanotubes (SWCNTs) was tuned electrochemically in acetonitrile electrolyte solution. In dry and oxygen-free solution, the electrochemistry of SWCNTs is controlled by capacitive charging. Reversible changes of intensity and frequency of the Raman spectra can be monitored during cyclic voltammetry at low scan rates. Electrochemical charging of SWCNTs can be also traced via reversible bleaching of the electronic transitions in the vis-NIR region. An aprotic medium offers a broader electrochemical window for tuning of electronic properties of SWCNTs. Electrochemical charging of SWCNTs in an aprotic electrolyte solution allows easy and precise control of the electronic structure of SWCNTs. In addition to commercial SWCNTs, a material made from gas-phase catalytic decomposition of CO by the HiPco process was also studied. Selective quenching of vis-NIR and Raman spectra is a useful tool to the analysis of tubes of varying diameter and helicity.

The Raman spectra of metallic tubes in SWCNTs (Single wall carbon nanotubes) bundles during electrochemical doping have been investigated using three different electrolyte solutions: LiClO 4 /CH 3 CN, LiClO 4 /propylenecarbonate/poly(methyl methacrylate) and LiClO 4 /polyethyleneimine. Precise control of the electrochemical charging enabled us to follow the detailed development of the tangential displacement (TG) mode of SWCNT bundles in dependence on the electrode potential. The response of the TG mode to electrode potential was dependent on electrolyte used as a consequence of different doping efficiency. We demonstrate that the liquid electrolyte solution (LiClO 4 /CH 3 CN) has superior doping efficiency to those of both the tested polymer electrolytes.

The electrochemical oxidation of polyaniline (PAni) films on gold electrodes is studied by simultaneous electron spin resonance (ESR) and UV−vis spectroelectrochemistry. The technique permits the separation of the superimposed UV−vis spectra of three redox states: the protonated reduced polyaniline chains, the deprotonated polaronic state, and the bipolaronic state. The separated UV−vis spectra as well as the potential dependence of each redox state concentration enables a more precise determination of the energy levels and the stability of paramagnetic species.

82 in agreement with the observation of a signal in electron spin resonance experiments [4 ‐ 6]. This view is also consistent with theoretical predictions [9] and with the analysis of the electron density distribution of a Y@C82 microcrystal as measured by x-ray diffraction [10]. Very few direct studies of the valency of the various endohedral metal ions have been reported. Xray photoemission spectroscopy (XPS) has been shown to be a suitable probe of the valency of the La in La@C82 [5,11]. In this case, the comparison of the La 3d core level spectrum with those of various La trihalides showed that the La is trivalent, with the sC82d 32 providing an environment slightly less electronegative than that in LaBr 3 [11]. In the case of the lanthanide monometallofullerene Tm@C82, a series of physical and chemical studies in solution of the three different isomers has been found to be consistent with a Tm 21 @C 22

Cyclic voltammograms are reported for C 6 0 (CF 3 ) n derivatives for the first time. The compounds studied were 1,9-C 6 0 (CF 3 ) 2 and 3 isomers of C 6 0 (CF 3 ) 1 0 , including the structurally characterized derivative 1,3,7,10,14,-17,23,28,31,40-C6o(CF3) 1 0 (C 6 0 (CF 3 ) 1 0 -3). The compound 1,9-C 6 0 (CF 3 ) 2 exhibited 3 reversible reductions; C 6 0 -(CF3) 1 0 -3 exhibited 2 reversible reductions; the other 2 isomers of C 6 0 (CF 3 ) 1 0 each exhibited 1 reversible reduction. ESR and near-IR spectroelectrochemical experiments were performed to characterize some of the C 6 0 (CF 3 ) n - and C 6 0 (CF 3 ) n 2 - species generated by cyclic voltammetry. The ESR spectrum of the C 6 0 (CF 3 ) 1 0 -3- radical anion consisted of an envelope of 25 lines centered at g = 2.0032 (the apparent a value is ca. 0.5 G), evidence of coupling between the unpaired electron and a significant number of the CF 3 fluorine atoms. The most significant finding is that this radical anion has a half-life in solution at 25 °C of about 7 min.

In all metallofullerenes known before this work, metal atoms form single highly polar bonds with non-metal atoms in endohedral cluster. This is rather surprising for titanium taking into account the diversity of organotitanium compounds. Here we show that the arc-discharge synthesis of mixed titanium-lutetium metallofullerenes in the presence of ammonia, melamine or methane unexpectedly results in the formation of TiLu2C@Ih-C80 with an icosahedral Ih(7) carbon cage. Single-crystal X-ray diffraction and spectroscopic studies of the compound reveal an unprecedented endohedral cluster with a μ3-carbido ligand and Ti-C double bond. The Ti(IV) in TiLu2C@Ih-C80 can be reversibly reduced to the Ti(III) state. The Ti=C bonding and Ti-localized lowest unoccupied molecular orbital in TiLu2C@Ih-C80 bear a certain resemblance to titanium alkylidenes. TiLu2C@Ih-C80 is the first metallofullerene with a multiple bond between a metal and the central, non-metal atom of the endohedral cluster. Metallofullerenes typically have polar single bonds between metals and non-metals. Here, through arc-discharge experiments, the authors observe the formation of an endohedral fullerene with an encapsulated tri-coordinate μ3-carbon centre and a stable titanium-carbon double bond.

The stabilization of carbon nanotubes via the filling with inner tubes is demonstrated by probing the optical transitions in double-walled carbon nanotube bundles under hydrostatic pressure with optical spectroscopy. Double-walled carbon nanotube films were prepared from fullerene peapods and characterized by HRTEM and optical spectroscopy. In comparison to single-walled carbon nanotubes, the pressure-induced redshifts of the optical transitions in the outer tubes are significantly smaller below $\sim$10 GPa, demonstrating the enhanced mechanical stability due to the inner tube already at low pressures. Anomalies at the critical pressure P$_d$$\approx$12 GPa signal the onset of the pressure-induced deformation of the tubular cross-sections. The value of P$_d$ is in very good agreement with theoretical predictions of the pressure-induced structural transitions in double-walled carbon nanotube bundles with similar average diameters., 6 pages, 4 figures; to appear in Phys. Rev. B

Lanthanides (Ln) find broad applications as contrast agents in medical imaging techniques such as magnetic resonance imaging (MRI).[1] MRI is one of the most powerful, noninvasive imaging procedures, which is able to create images of tissues, organs and diseases in vivo.[2, 3] Every year, about six million patients undergo MRI studies of which 30 % are performed using Gd-based contrast agents (CAs), which significantly reduce the spin-lattice relaxation time T1 of water protons leading to an increase of the signal intensity and improved contrast.[4] Although medical applications of lanthanides in imaging are dominated by Gd3+, other lanthanides can be also used as MRI[1, 5] CAs (e.g., Dy3+ is considered as an efficient contrast agent for high-field MRI[6]) and X-ray CAs.[7, 8] Radioisotopes of lanthanides (especially 177Lu) are employed as therapeutic radiopharmaceuticals.[9]

The density functional theory calculations of molecular structure and spectroscopic and electronic properties of charged states in four triazine-heteroaryl star-shaped compounds are presented. The molecules end-capped with different heteroaryl groups, i.e., thiophene (TTT1), furan (TFT2), 3,4-ethylenedioxythienyl (TET3), and thiazole (TSNT4), were studied by electrochemical and in situ ESR/UV-vis-NIR spectroelectrochemical techniques in tetrahydrofuran/(TBA)BF(4). The charged states of monomers were created by cathodic reduction and the stability of generated anion radicals was characterized in detail both experimentally and theoretically. The TET3 molecule resulted in a star-shaped hyperbranched polymer formed anodically which in turn can be reversibly oxidized up to the tetracation. The nature and charge distribution of charge carriers at each redox state in the as-prepared polymer was clarified by calculations for the model (TET3)(3) trimer structure.

The influence of the molecular structure on the stabilization of charged states was studied in detail by in situ ESR UV-vis NIR spectroelectrochemistry at a novel α,ω-dicyano substituted β,β'-dibutylquaterthiophene (DCNDBQT) and the electrochemically generated cation and anion radicals have been proved for the first time. The voltammetry of DCNDBQT results in two separate oxidation steps with the reversible first one. The experimental absorption maxima at 646 and 1052 nm together with the calculated ones (by DFT method) as well as an ESR signal at the first anodic step prove the presence of a radical cation. Three additional optical bands (554, 906, and 1294 nm for CT-transition) can be attributed to the formation of cation radical dimer. The dicationic structure formed in the second oxidation step is not stable. The stabilization proceeds via a dimer formation in two chemical follow-up reactions. The existence of the dimeric structures was proved by ex situ MALDI TOF mass spectrometry. As the substitution by cyano groups opens the route to cathodic reductions, DCNDBQT shows a single quasi-reversible reduction step. Here, the in situ ESR UV-vis NIR spectroelectrochemical measurements and theoretical calculations let us confirm the electrochemical generation of an anion radical. As we found a low number of anion radicals by quantitative ESR spectroelectrochemistry and an appearance of additional bands in the UV-vis NIR absorption spectra, the formation of dimeric structures must be considered and was corroborated by mass spectrometry. The role of dimerization in the reaction mechanism of the DCNDBQT oxidation and reduction are discussed in general. The experimental results were interpreted using the quantum chemical calculations based on density functional theory.

To achieve higher efficiencies in organic solar cells, ideally the open circuit voltage (VOC), fill factor (FF) as well as the short current density (JSC) have to be further improved. However, only a few suitable acceptor molecules, e.g. C60, are currently available for the photoactive layer. Despite a good electron mobility on the order of 1×10−3 cm2/Vs the absorption of C60 in the visible sun spectrum is low. From polymer based solar cells it is known that the fullerene derivative [70]PCBM used in the photoactive layer shows a significant enhancement in J compared to [60]PCBM. This work investigates the application of fullerene C70 as acceptor in comparison to the well known C60 in vacuum processed small molecule solar cells. C70 shows a broadened and red shifted absorption (abs. maximum around 500 nm) compared to C60. By fabricating p-i-i solar cells we show that the stronger absorption of C70 leads to enhanced photon harvesting and increased external quantum efficiency. The bulk heterojunction p-i-i solar cell containing C70 as acceptor and ZnPc as donor, co-evaporated with an optimized ratio of 2:1, and a layer thickness of 30 nm shows improved solar cell parameters: a 30% larger photocurrent of 10.1 mA/cm2 is obtained. The VOC of 0.56 V and FF of 55% remain comparable to C60-containing p-i-i solar cells. Therefore, the solar cell performance is mainly improved by JSC and leads to a mismatch corrected power conversion efficiency of 3.12%. Thus, we show that C70 is an alternative fullerene to C60 for solar cell applications. © 2010 Copyright SPIE - The International Society for Optical Engineering.

The redox behavior of N,N,N',N'-tetrakis(4-aminophenyl)benzidine (A) and its N,N,N',N'-tetrakis(4-methoxyphenyl)-substituted analogue (B) was studied in detail by a new designed in situ thin layer electron spin resonance (ESR)/UV-vis-NIR spectroelectrohemical cell. The spectroelectrochemical studies of cation radicals, dications, and tetracations indicate a strong difference in stability of higher ions of two model compounds with different phenyl substitution. In cyclovoltammetry the small peak separation of the first two oxidation peaks for both compounds points to a small energetic difference in the first two electron transfers, while the peak separation of the second and third peak is quite large. A well resolved ESR spectrum of the B(*+) cation radical with dominating splittings from two nitrogen atoms is observed and an ESR silent product was determined at the third oxidation peak for both compounds, confirming the formation of a tetracation by a two electron transfer at the third voltammetric peak. In contrast to structure A a more complex redox behavior was found for B under voltammetric cycling. The reaction mechanism indicates the transformation of B in a new product P with a carbazole moiety. This compound can form a highly stabilized cation radical P(*+). A theoretical study based on density functional theory calculations has clarified the role of charging in changes to the structures of both triarylamine derivatives A and B.

The role of the phenazine structure in the stabilization of charged states in polyaniline was studied by in situ electron spin resonance (ESR)-UV/vis-near-infrared (NIR) spectroelectrochemistry of polyaniline and the copolymers of aniline and a phenazine derivative (3,7-diamino-5-phenylphenazinium chloride, phenosafranine). It is shown that the copolymer can be prepared by electropolymerization, and its structure was confirmed by mass spectrometry and IR spectroscopy. The electrochemistry of polyaniline and its copolymer pointed to preferred stabilization of a polaron pair in the charged states at the initial charge transfer reaction instead of polarons that are formed by equilibrium reaction at higher electrode potentials. A second polaron pair is detected for higher doped states of the polymer films. A mechanism of the formation of charged states in polyaniline and their equilibrium is given. It is shown that in situ ESR-UV/vis-NIR spectroelectrochemistry is the method of choice to differentiate between polarons and polaron pairs in their potential-dependent formation. Thus, by this in situ spectroelectrochemical method the influence of phenazine structure on the formation of polarons in aniline polymers and copolymers can be followed.

The inter- and intramolecular ordering of the trimetallic nitride endohedral fullerene ${\text{Dy}}_{3}\text{N}@{\text{C}}_{80}$ with icosahedral cage symmetry ${I}_{h}$ on Cu(111) has been studied by scanning tunneling microscopy and synchrotron-based x-ray photoelectron diffraction (XPD). ${\text{Dy}}_{3}\text{N}@{\text{C}}_{80}$ $({I}_{h})$ is found to form ordered islands consisting of domains of equally oriented molecules. As for ${\text{C}}_{60}$ on the same substrate, the cage is facing with a hexagon toward the surface, which is however slightly tilted for ${\text{C}}_{80}$. The endohedral nitrogen atom remains at a position close to the geometrical center of the cage. Resonant XPD on the ${\text{M}}_{\text{V}}$ edge shows that the encaged ${\text{Dy}}_{3}\text{N}$ unit takes well-defined orientations with respect to the ${\text{C}}_{80}$ cage and the Cu(111) substrate.

The first spectroscopic characterization of the dimeric dicationic fullerene complex [(C(70))(2)](2+)(Ti(3)Cl(13))(-)(2) is reported and supported by DFT calculations. The IR spectrum of the dimer is interpreted in terms of the normal modes of the pristine C(70), and the effects of charging C(70) and the intercage bond formation between C(70) units on the IR spectrum are discussed. Analysis of the vibrational spectrum of the anion, Ti(3)Cl(13)(-), is also provided. NIR absorption and fluorescence spectra of the complex are studied, and the dimer is shown to have a small HOMO-LUMO gap of 0.8 eV. The electronic structure of [(C(70))(2)](2+) is studied with the use of DFT and compared to that of the other single-bonded fullerene dimers, including [(C(70))(2)](2-), (C(69)N)(2), and [(C(60))(2)](2-). Characteristic features in the vibrational spectra and electronic structure of all single-bonded fullerene dimers are revealed.

In situ spectroelectrochemistry is of high importance for the characterization of doping reactions in pi-conjugated polymers. In this paper we present the results of simultaneous ESR and UV-vis-NIR measurements performed in situ during electrochemical p- and n-doping of polyazulene (PAz). In previous studies on p-doping of PAz the assignment of the optical absorption bands to specific charge carriers have been somewhat controversial, therefore the aim of this study is to clarify the nature of the doping-induced charge carriers and their corresponding optical absorption bands by in situ ESR-UV-vis-NIR spectroelectrochemistry. PAz was polymerized in two different potential ranges in order to obtain films with different structures and morphologies. On the basis of our spectroelectrochemical results we propose that polarons and polaron pairs are formed during p-doping in the two different types of PAz films electrodeposited on ITO. For studying n-doping of PAz, a Pt electrode was used. The ESR signal first decreased in intensity at low doping levels and then increased in intensity at higher doping levels pointing to the formation of new paramagnetic species. At high negative potentials there occurred an additional line broadening of the ESR signal indicating the existence of rather localized negative charge carriers.

Molecular structure of Dy3N@C78 and Tm3N@C78 clusterfullerenes are addressed by the IR and Raman vibrational spectroscopic studies and DFT computations. Firstly, extensive semiempirical calculations of 2927 isomers of C78 hexaanions followed by DFT optimization were applied to establish their relative stability. Then, DFT calculations of a series of M3N@C78 (M=Sc, Y, Lu, La) isomers were performed which have shown that the stability order of the isomers depends on the cluster size. While the Sc3N cluster is planar in the earlier reported Sc3N@C78 (D3h: 24109) clusterfullerene, relatively large Y3N and Lu3N clusters would be forced to be pyramidal inside this cage, which would result in their destabilization. Instead, these clusters remain planar in the non-IPR C2: 22010 isomer making Y3N@C78 and Lu3N@C78 clusterfullerenes with this cage structure the most stable ones. Finally, on the basis of a detailed analysis of their IR and Raman spectra supplemented with DFT vibrational calculations, the recently isolated Tm3N@C78 and the major isomer of Dy3N@C78 are assigned to the non-IPR C2: 22010 cage structure. A detailed assignment of their experimental and computed IR and Raman spectra is provided to support this conclusion and to exclude other cage isomers.

Dysprosium-based trimetallic nitride endohedral fullerenes (clusterfullerenes)-the Dy(3)N@C(2)(n) (38

In this letter, we show for the first time the use of metal oxides as catalysts in the synthesis of single-walled carbon nanotubes (SWCNTs) using laser ablation. Further, SWCNTs have been synthesized at low temperature (down to room temperature), where their nucleation cannot be explained via fullerene nucleation. The data point to a nucleation mechanism previously not identified, that places a stable oxidized ring as the root cause for the growth of SWCNTs.

[reaction: see text] A series of alpha,alpha'-bisdiarylamino-capped oligothiophenes C(n) were prepared by the palladium-catalyzed reaction of the dibromo compounds A(i) with diarylamines, N,N-diarylamino-substituted thiophenes or 2,2'-bithiophenes BX(j). These easily oxidizable compounds exhibit a high tendency to form amorphous glasses and characteristic electrochemical and spectroscopic properties that depend significantly on the number of their thiophene moieties.