Search

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 electrochemical reduction behaviour of a new promising energetic material 2,2-dinitroethene-1,1-diamine (FOX-7) was investigated in acetonitrile, dimethylformamide and dimethylsulfoxide at mercury, platinum, gold and glassy carbon electrodes. Instead of expected consumption of four to eight electrons necessary for reduction of nitro groups, only two electrons are consumed. In acetonitrile, the starting form of FOX-7 is the olefinic, nearly planar structure polarized by the push-pull effect, the first electron attacks one of the nitro groups. The electrochemical as well as in situ UV-vis-NIR and EPR spectroelectrochemical results are in agreement with autoprotonation reduction mechanism. The radical intermediate was intercepted and identified by EPR spectrometry where an alternation line-width (AL) effect was observed.

The first intermediates of electrochemical reduction of nitro compounds in nonaqueous DMF are stable radical anions. In the series of mono-, di-, tri- and tetranitro calix[4]arenes each nitro group represents a reduction center, therefore the question about the spin state of intermediary anions arises. In this communication, the voltammetric and coulometric investigation of these compounds is performed together with the spectral measurements (ESR and UV-vis). The in-situ spectroelectrochemical approach proved that during reduction, in all polynitro radicalic intermediates the electrons remain unpaired and thus relatively stable mono-, di-, tri- and tetraradical mono-, di-, tri- and tetraanions, respectively, can be electrochemically generated in aprotic DMF from polynitrocalix[4]arenes. This finding confirms that the nitrophenyl units in polynitrocalix[4]arenes are completely independent and no mutual electronic communication takes place among them.

A detailed spectroelectrochemical and theoretical study of thienyl derivatives based on pyrene, namely 1-(2-thienyl)-pyrene (1), 1,6-bis(2-thienyl)-pyrene (2), 1,4-bis(2-thienyl)-pyrene (3), 1,3,6-tris(2-thienyl)-pyrene (4) and 1,3,6,8-tetra(2-thienyl)-pyrene (5), and their oxidation products with focus on the formation of their corresponding cationic states are presented. Regioregular polymeric systems were prepared by means of electrochemical polymerization from monomers 2–4. The redox behavior of the corresponding polymers was studied by cyclic voltammetry and in situ EPR/UV–vis–NIR spectroelectrochemistry with the aim of obtaining details on the type of charge carriers within the polymer film. Quantum chemical calculations of the optimal geometries and optical transitions for the neutral and charged forms were performed in order to reveal the influence of electrochemical oxidation on the molecular structure of the monomers and corresponding dimers and/or polymers.

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.

Poly(2-methoxynaphthalene) (P2MN) belongs to the category of fused ring organic semiconductors that due to their planar structure have very interesting optical and electrical properties like a reduced band gap and easiness of undergoing both oxidation and reduction. Here, we present a spectroelectrochemical study by means of simultaneous recording of electron spin resonance–UV–vis–near infrared spectra (ESR–UV–vis–NIR) to probe the nature of the charge carriers in both p- and n-doped P2MN. As shown earlier P2MN is both p- and n-dopable, however, further information of the nature of both types of charge carriers is needed. In this work we demonstrate that the dominant charge carrier in p- and n-doped P2MN is positive and negative polarons, respectively. The material under study constitutes an example of an ambipolar organic conjugated polymer capable to conduct both holes and electrons. This is a unique property worthy to be further studied since only a few organic conducting polymers can reversibly be both p- and n-doped.

Infrared spectra of La2@C80 and a series of Ce-based endohedral metallofullerenes (EMFs), including Ce@C82, Ce2@C72, Ce2@C78, and Ce2@C80 are reported. DFT calculations are used for their thorough analysis and assignment. The vibrations of the fullerene cages in all studied EMFs differ from those of their empty, charged cage analogues. Furthermore, EMFs with the same carbon cage but different type of encapsulated species also show significant differences in their cage vibrational patterns. These phenomena are explained by a different coupling of the vibrational modes as well as by the different charge distributions in EMFs and empty, isostructural fullerene anions.

The three diphenylamino-endcapped thiophene compounds 1,4-bis-(2-diphenylamino-thiophen-5-yl)-benzene ( A ), 1,4-bis-[2-(phenothiazin-10-yl)-thiophen-5-yl]-benzene ( B ), and 1,4-bis-(5-diphenylamino-[2,2′]bithiophen-5′-yl)-benzene ( C ) with a central phenylene core were investigated by in situ ESR/UV–vis–NIR and in situ NMR spectroelectrochemistry and quantum chemical studies. The computed vertical ionization potentials are 4.85 eV for A , 5.39 eV for B and 4.80 eV for C while the adiabatic ionization potentials are slightly lower 4.45 eV (for A ), 4.96 eV (for B ) and 4.47 eV (for C ). The minimal difference between computed ionization potentials of A and C and the lower oxidation ability of B are in good agreement with the experimental electrochemical findings with the first half-wave anodic potentials 0.69 V (for A ), 0.81 V (for B ) and 0.67 V (for C ), all vs. decamethylferrocene (DmFc + /DmFc). For the radical monocations A + and C + the spin delocalisation on the central phenylene moiety was confirmed both experimentally and by theoretical calculations. For the radical cation B + , the presence of a phenothiazinyl moiety is responsible for the delocalization of unpaired electron in the lateral part of this molecule. The stability of the charged states was increased substantially by the incorporation of two further 2,5-thienylene moieties between the central moiety and the side groups in C . Detailed spectroelectrochemical studies of the cation radical, dication, trication and tetracation of C are in good agreement with the calculated electronic transitions and experimental values for all redox states. In situ NMR spectroelectrochemical studies at different temperatures indicate dimerisation reactions of charged 1,4-bis-(5-diphenylamino-[2,2′]bithiophen-5′-yl)-benzenes.

A series of various thienyl derivatives of pyrene were synthesized by Stille cross-coupling procedure. Their structures were characterized by (1)H NMR, (13)C NMR and elemental analysis. The spectroscopic characteristics were investigated by UV-vis absorption and fluorescence spectra. Based on quantum chemical calculations, the energy levels of investigated molecules with respect to the pyrene molecule were also discussed.

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.

Electrochemical and NMR spectroscopic studies prove the endohedral oxidation of CeIII in nitride clusterfullerenes CeM2N@C80 (M = Sc, Y, Lu). The redox potential of the endohedral CeIV/CeIII couple...

A radical-anion of [5,6]-pyrrolidine-Sc3N@C80 is generated both chemically and electrochemically and studied by ESR spectroscopy. The rotation of the Sc3N cluster is shown to be frozen on the ESR time scale resulting in nonequivalent Sc atoms with hyperfine coupling constants noticeably smaller than in the radical anion of the pristine Sc3N@C80 but larger than in any other derivatives of Sc3N@C80. Experimental ESR studies are supported by extended DFT calculations of the cluster rotational pathways, spin density distribution, and hyperfine coupling constants.

We demonstrate a single-molecule switch based on tunneling electron-driven rotation of a triangular Sc3N cluster within an icosahedral C80 fullerene cage among three pairs of enantiomorphic configurations. Scanning tunneling microscopy imaging of switching within single molecules and electronic structure theory identify the conformational isomers and their isomerization pathways. Bias-dependent action spectra and modeling identify the antisymmetric stretch vibration of Sc3N cluster to be the gateway for energy transfer from the tunneling electrons to the cluster rotation. Hierarchical switching of conductivity through the internal cluster motion among multiple stationary states while maintaining a constant shape, is advantageous for the integration of endohedral fullerene-based single-molecule memory and logic devices into parallel molecular computing architectures.

The clusterfullerene Sc(4)O(2)@C(80) with a mixed redox state of scandium was found to be an exciting molecule for endohedral electrochemistry as demonstrated by means of an in situ electron spin resonance (ESR) spectroelectrochemical study of the spin density distribution in its electrochemically generated cation and anion radicals. The compound exhibits two reversible reduction and oxidation steps with a relatively small electrochemical gap of 1.10 V. The ESR spectra of the ion radicals have a rich hyperfine structure caused by two pairs of equivalent Sc atoms. The Sc-based hyperfine structure with large hyperfine coupling constants shows that both oxidation and reduction of Sc(4)O(2)@C(80) are in cavea redox processes, which is the subject of endohedral electrochemistry. The assignment of the experimentally determined a((45)Sc) values to the two types of Sc atoms in the Sc(4)O(2) cluster was accomplished by extended density functional theory and molecular dynamics simulations. Sc atoms adopting a divalent state in the neutral Sc(4)O(2)@C(80) exhibited an especially large coupling constant of 150.4 G in the cation radical, which is the record high a((45)Sc) value for Sc-based endohedral metallofullerenes. Such a high value is explained by the nature of the highest occupied molecular orbital (HOMO) localized on the six-atom Sc(4)O(2) cluster. This HOMO is a Sc-Sc bonding MO and hence has large contributions from the 4s atomic orbitals of Sc(II). We claim that ESR spectroelectrochemistry is an invaluable experimental tool in the studies of metal-metal bonding in endohedral metallofullerenes and in endohedral electrochemistry.

In situ electron spin resonance (ESR) spectroelectrochemical and thermoelectrochemical studies of the non-substituted α - and the alkyl substituted (in α , ω -positions) sexithiophenes as single molecules in solution are presented. Thus any influence of interactions of the molecules in the solid state is avoided. In nitrobenzene solution the life time of the cation radicals is sufficiently high to detect and characterize them by in situ ESR spectroscopy. Furthermore, the α -sexithiophene ( α -6T) was found to form insoluble films at the electrode surface by dimerization and polymerization while no film deposition at the electrode was detected for the end-capped α , ω -dihexylsexithiophene (DH-6T). In thermoelectrochemical experiments with continuous heating during anodic polarization, the polymer formation appears to be completely stopped. Obviously, the thermal stirring prevents the deposition of the generated polymer at the heated surface. The voltammetric waves corresponding to the radical cation or even the dication formation keep maintained in CV with permanent heating as well as with temperature-pulse voltammetry (TPV). With heating pulses being too short to initialize convection, the behavior was found different from that with permanent heating. Here, the polymerization at room temperature even with a somewhat increased rate causes a film formation at the electrode.

The synthesis, isolation and spectroscopic characterization of holmium-based mixed metal nitride clusterfullerenes Ho(x) Sc(3-x) N@C(80) (x=1, 2) are reported. Two isomers of Ho(x) Sc(3-x) N@C(80) (x=1, 2) were synthesized by the reactive gas atmosphere method and isolated by multistep recycling HPLC. The isomeric structures of Ho(x) Sc(3-x) N@C(80) (x=1, 2) were characterized by laser-desorption time-of-flight (LD-TOF) mass spectrometry and UV/Vis/NIR, FTIR and Raman spectroscopy. A comparative study of M(x) Sc(3-x) N@C(80) (M=Gd, Dy, Lu, Ho) demonstrates the dependence of their electronic and vibrational properties on the encaged metal. Despite the distinct perturbation induced by 4f(10) electrons, we report the first paramagnetic (13) C NMR study on Ho(x) Sc(3-x) N@C(80) (I; x=1, 2) and confirm I(h) -symmetric cage structure. A (45) Sc NMR study on HoSc(2) N@C(80) (I, II) revealed a temperature-dependent chemical shift in the temperature range of 268-308 K.

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.

Titanium/yttrium mixed metal nitride clusterfullerene (MMNCF) TiY(2)N@C(80) has been successfully synthesized, representing the first Ti-containing non-scandium MMNCF. TiY(2)N@C(80) has been isolated by multistep HPLC and characterized by various spectroscopies in combination with DFT computations. The electronic absorption property of TiY(2)N@C(80) was characterized by UV-vis-NIR spectroscopy, indicating the resemblance to that of TiSc(2)N@C(80) with broad shoulder absorptions. The optical band gap of TiY(2)N@C(80) (1.39 eV) is very close to that of TiSc(2)N@C(80) (1.43 eV) but much smaller than that of Y(3)N@C(80)(I(h), 1.58 eV). Such a resemblance of the overall absorption feature of TiY(2)N@C(80) to TiSc(2)N@C(80) suggests that TiY(2)N@C(80) has a similar electronic configuration to that of TiSc(2)N@C(80), that is, (TiY(2)N)(6+)@C(80)(6-). FTIR spectroscopic study and DFT calculations accomplish the assignment of the C(80):I(h) isomer to the cage structure of TiY(2)N@C(80), with the C(1) conformer being the lowest energy structure, which is different from the C(s) conformer assigned to TiSc(2)N@C(80). The electrochemical properties of TiY(2)N@C(80) were investigated by cyclic voltammetry, revealing the reversible first oxidation and first reduction step with E(1/2) at 0.00 and -1.13 V, respectively, both of which are more negative than those of TiSc(2)N@C(80), while the electrochemical energy gap of TiY(2)N@C(80) (1.11 V) is almost the same as that of TiSc(2)N@C(80) (1.10 V). Contrary to the reversible first reduction step, the second and third reduction steps of TiY(2)N@C(80) are irreversible, and this redox behavior is dramatically different from that of TiSc(2)N@C(80), which shows three reversible reduction steps, indicating the strong influence of the encaged group-III metal (Y or Sc) on the electronic properties of TiM(2)N@C(80) (M = Y, Sc).

Graphene|metal|ligand systems open a new realm in surface magnetochemistry. We show that by trapping metal atoms in the two-dimensional potential lattice of a graphene-ligand interface it is possible to build a chemical analogue of an optical lattice, a key setup in quantum information and strongly correlated systems. Employing sophisticated first-principles calculations, we studied electronic and dynamic properties of graphene|metal|ligand assemblies and showed that there is a general principle--spin-charge separation in π-d systems--that underlies the possibility of synthesizing and controlling such systems. We find that ligands can work as a local gate to control the properties of trapped metal atoms and can impose bosonic or fermionic character on such atomic nets, depending on the ligand's nature. Remarkably, the magnetization energy in such systems reaches record-high values of ca. 400 meV, which makes the respective magnetic phenomena utilizable at room temperature. Accompanied by spin polarization of the graphene π-conjugated system it leads to spin-valve materials and brings the realization of quantum computing one step closer.

A combined in situ NMR and in situ ESR spectroelectrochemical study of a reaction mechanism is presented detecting and describing the whole number of paramagnetic and diamagnetic intermediates and final products in an electrode reaction. While in situ NMR spectroelectrochemistry provides a powerful method for the study of structural or electronic changes of diamagnetic molecules in any electrochemical reaction mechanism, in situ ESR spectroelectrochemistry is the method of choice to detect paramagnetic structures and to characterise their electronic state via the g-value and hyperfine splitting in redox reactions. To demonstrate the power of this combination of magnetic spectroscopies in electrochemistry, the reduction of p-benzoquinone to hydroquinone is followed by both these spectroelectrochemical methods at selected pH values, thus considering the influence of the proton on the reaction mechanism. The results of both in situ spectroelectrochemical methods at the same redox system are used to get the complete reaction mechanism of p-benzoquinone at electrodes in aqueous solutions.

We observed the lowest HOMO–LUMO energy transition estimated to be only 1.06 eV for the full-cage-shaped emerald-green fullerene EF-6MC4t. This energy value was derived from the intercept of characteristic double-absorption bands at 1014 (1.23 eV) and 1084 nm (1.14 eV) in the NIR spectrum and the first fluorescence emission band centered at 1278 nm (0.97 eV).

While the role of asymmetric nitride clusters on the cage size and symmetry in fullerene-based structures is known, the role of the asymmetric arrangement of metals in nitride clusters on the nitrogen is not studied now. It is discovered that asymmetric mixed-metal nitride clusters give sufficiently narrow 14 N NMR signals to make NMR the method of choice to characterize the endohedral cluster from the inside. In the series of mixed-metal nitride clusterfullerenes Lu x Sc 3-x N@C 80 and Lu x Y 3-x N@C 80 (x = 0-3) the δ( 14 N) values are found to be linear functions of x showing that 14 N chemical shifts are additive values with specific increment for each kind of metal atoms. DFT calculations are performed to interpret the experimentally measured spectra. To reveal the main factors affecting 14 N chemical shifts in nitride clusterfullerenes, shielding tensor components are analyzed in terms of Ramsey theory both in localized and canonical molecular orbitals. 14 N chemical shifts in M 3 N@C 80 and related systems are shown to be determined solely by nitrogen-localized orbitals, and in particular by the p x,y,z atomic orbitals of nitrogen. As a result, the peculiarities of the nitrogen shielding in nitride clusterfullerenes can be interpreted by the simple analysis of the nitrogen-projected density of states and its variation in different chemical environments.

The determination of the actual electrode surface temperature is important for all electrochemical methods using in situ heating of electrodes. Existing methods of temperature measurement of a heated thin-wire electrode are of restricted use and critically discussed in the introduction. The use of the electrode wire itself as a resistive thermometer is improved in the present method. With the new thermoelectrochemical method temperature pulse voltammetry, the reliability of different thermometric methods can be compared. In this way, it is ensured to have correct temperature measurements at wire microelectrodes in all common solvents available.

To consider the past, present and future of in situ spectroelectrochemistry, a review on the recent state of modern spectroelectrochemistry and trends in the development of spectroelectrochemcial techniques is presented for the combined application of different in situ spectroelectrochemcial methods like ESR spectroelectrochemistry, NMR spectroelectrochemistry, Raman spectroelectrochemistry or IR spectroelectrochemistry to electrode systems. Starting with a discussion of the first steps in spectroelectrochemistry in the past, the main part of this review is focused on the advantages of the combined application of spectroelectrochemical techniques in the analysis of electrode reactions. The spectroelectrochemical methods are demonstrated to be successful in electrode reactions both for solid structures like polymers or carbon nanotubes and for molecular structures like fullerenes and oligothiophenes. The final outlook is attributed to future developments in spectroelectrochemistry.

In contrast with empty fullerenes, nitride clusterfullerenes usually exhibit irreversible reduction steps at moderate electrochemical scan rates. However, these reduction steps are chemically reversible, indicating that reversible follow-up reaction takes place. To explain this phenomenon, we analyze in this work if anion-radicals of nitride clusterfullerenes are more prone to dimerization than anion-radicals of empty fullerenes. Extensive DFT computations are performed to find the most stable dianionic dimeric structures of Sc3N@C68, Sc3N@C80, Sc3N@C80(CF3)2, [5,6] and [6,6] pyrrolidine adducts of Sc3N@C80 and Y3N@C80, a series of Y3N@C2n (2n = 78, 80, 84, 86, 88), as well as those of empty fullerenes C60, C70, and C84. Dimerization energies of the most stable isomers are computed in the gas phase, with the use of van der Waals corrections, and in solution. It is found that dianionic dimers of nonderivatized nitride clusterfullerenes are substantially more stable than those of empty fullerenes, which can...

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.

Electron transfer to/from endohedral metallofullerenes usually leads to population/depopulation of the fullerene-based molecular orbitals. However, for certain EMFs, endohedral redox activity was discovered, and the number of such fullerenes is continuously increasing with the developments in EMF synthesis and fulfillment of more dedicated studies of their properties. In this Perspective, the state of the art in the emerging field of endohedral (in cavea) electrochemistry is reviewed. We describe representative examples of EMFs that exhibit endohedral electrochemical activity and discuss the special phenomena (spin−charge separation, spin flow dynamics) accompanying endohedral redox reactions.

A novel pyrene-functionalized poly(3-hexylthiophene) (P3HT) derivative (Pyrene-P3HT) has been successfully synthesized via a postpolymerization approach, and its noncovalent interactions with SWNTs are studied in detail based on its composite of SWNT (SWNT/Pyrene-P3HT). The molecular structure of Pyrene-P3HT is confirmed by 1H NMR spectroscopy, revealing a ca. 15% substitution ratio of pyrene within Pyrene-P3HT. The noncovalent interactions between SWNT and Pyrene-P3HT are studied by UV−vis/NIR and Raman spectroscopy as well as ESR spectroelectrochemical experiments and compared to those between SWNT and P3HT. The UV−vis/NIR spectra of SWNT/Pyrene-P3HT are found to be independent of the blending ratio of SWNTs and Pyrene-P3HT, indicating that the electronic structures of SWNTs are basically intact after blending Pyrene-P3HT. Raman spectra of SWNT/Pyrene-P3HT and SWNT/P3HT are quite different, pointing to their difference on the interactions between SWNTs and P3HT. The in situ ESR spectroelectrochemical st...

The role of dendrimer structure on the spin density distribution in radical cations was studied for five 1,4-phenylenediamine dendrimers, representing PAMAM-like dendrimer generations ranging from ...

A family of highly stable (poly)perfluoroalkylated metallic nitride cluster fullerenes was prepared in high-temperature reactions and characterized by spectroscopic (MS, (19)F NMR, UV-vis/NIR, ESR), structural and electrochemical methods. For two new compounds, Sc(3)N@C(80)(CF(3))(10) and Sc(3)N@C(80)(CF(3))(12,) single crystal X-ray structures are determined. Addition pattern guidelines for endohedral fullerene derivatives with bulky functional groups are formulated as a result of experimental ((19)F NMR spectroscopy and single crystal X-ray diffraction) studies and exhaustive quantum chemical calculations of the structures of Sc(3)N@C(80)(CF(3))(n) (n = 2-16). Electrochemical studies revealed that Sc(3)N@C(80)(CF(3))(n) derivatives are easier to reduce than Sc(3)N@C(80), the shift of E(1/2) potentials ranging from +0.11 V (n = 2) to +0.42 V (n = 10). Stable radical anions of Sc(3)N@C(80)(CF(3))(n) were generated in solution and characterized by ESR spectroscopy, revealing their (45)Sc hyperfine structure. Facile further functionalizations via cycloadditions or radical additions were achieved for trifluoromethylated Sc(3)N@C(80) making them attractive versatile platforms for the design of molecular and supramolecular materials of fundamental and practical importance.

The synthesis of a novel alkali metal aluminium borohydride NaAl(BH4)xCl4 x from NaBH4 and AlCl3 using a solid state metathesis reaction is described. Structure determination was carried out using synchrotron powder diffraction data and vibrational spectroscopy. An orthorhombic structure (space group Pmn21) is formed which contains Na+ cations and complex [Al(BH4{}Cl)4] anions. Due to the high chlorine content (1 [less than or equal] x [less than or equal] 1.43) the hydrogen density of the borohydride is only between 2.3 and 3.5 wt. H2 in contrast to the expected 14.6 wt. for chlorine free NaAl(BH4)4. The decomposition of NaAl(BH4)xCl4 x is observed in the target range for desorption at about 90 [degree]C by differential scanning calorimetry (DSC){} in situ Raman spectroscopy and synchrotron powder X ray diffraction. Thermogravimetric analysis (TG) shows extensive mass loss indicating the loss of H2 and B2H6 at about 90 [degree]C followed by extensive weight loss in the form of chloride evaporation.

A series of various substituted 1,3,5-triarylbenzenes, 2,4,6-triaryl-1-phenoles, 1,3,5-triaryl-1-methoxybenzenes and 2,4,6-triaryl-1,3,5-trimethoxybenzenes were synthesized by a Stille cross-coupling procedure. Their structures were confirmed by 1H NMR, 13C NMR, and elemental analysis. Containing thienyl, furyl and EDOT groups polymers obtained in the process of electropolymerization could be carefully considered as a building material in a wide range of organic-electronic devices. We compare properties of monomers and related polymers depending on aryls moieties and their influence of hydroxyl and methoxyl groups attached to the central benzene core.

New experimental results on perfluoroalkylation of C{sub 60} and C{sub 70} with the use of R{sub f}I (R{sub f} = CF{sub 3}, C{sub 2}F{sub 5}, n-C{sub 3}F{sub 7}, n-C{sub 4}F{sub 9}, and n-C{sub 6}F{sub 13}), along with a critical overview of the existing synthetic methods, are presented. For the selected new fullerene (R{sub f}){sub n} compounds we report spectroscopic, electrochemical and structural data, including improved crystallographic data for the isomers of C{sub 70}(C{sub 2}F{sub 5}){sub 10} and C{sub 60}(C{sub 2}F{sub 5}){sub 10}, and the first X-ray structural data for the dodecasubstituted perfluoethylated C{sub 70} fullerene, C{sub 70}(C{sub 2}F{sub 5}){sub 12}, which possesses unprecedented addition pattern.

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 charged states of C(60)(CF(3))(2n) (2n = 2-10) derivatives have been studied by electron spin resonance (ESR) and vis-near-infrared (NIR) spectroelectrochemistry. The anion radicals and diamagnetic dianions were furthermore described by theoretical calculations. The ESR spectra of anion radicals exhibit complex patterns due to multiple CF(3) groups. Their interpretation is accomplished by DFT calculations with B3LYP functional. It is shown that calculations provide reliable results when the extended aug-cc-pCVTZ basis set is used for fluorine atoms; however, specially tailored basis sets such as EPR-III also give very similar results with only a fraction of the computational cost. Absorption spectra of the anions exhibit NIR absorption bands, whose assignment is provided by time-dependent DFT calculations.

A series of novel oligoarylenes based on donor–acceptor system, containing triazine moiety as an electron-transporting central core, have been prepared by electrochemical polymerization. The redox behaviour of poly(2,4,6-tri[p-(2-(3,4-ethylenedioxythienyl))-phenyl]-1,3,5-triazine) was studied by cyclic voltammetry and triple in situ ESR/UV–vis–NIR spectroelectrochemistry to get more details on the type of charge carriers within the film. To obtain desired oligoarylenes, triazine-core monomers possessing various electrochromic side groups have been synthesized by the Stille cross-coupling methodology. The structures have been confirmed by 1H NMR, 13C NMR, and elemental analysis. Monomers show good chemical stability in common organic solvents such as chloroform, dichloromethane or toluene and also exhibit excellent thermal stability over wide range of temperatures. Furthermore, their photophysical properties have been established with the use of fluorescence spectroscopy. Electrochemical results accompanied with fluorescence spectroscopy suggest that these derivatives of triazine can be successfully used in the fabrication of organic light-emitting diodes (OLEDs).

A detailed study on the relaxation mechanisms of higher cage fullerene sizes is done as a prerequisite for studies of the influence of the endohedral structures on fullerene cage carbon relaxation. Recent studies of the dynamic behavior of C(60) and C(70) in aromatic solvents and CS(2) solution show the influence of the shape and the symmetry of the cage to be highly important as well as the influence of the solvent to be negligible. As higher fullerene cages have more than one stable isomer, the isolation of isomeric pure structures is of high importance for a detailed study of the dynamic behavior of such fullerenes. Here we investigated the three higher fullerene cage isomers D(2)-C(76), C(2v)(3)-C(78), and D(2)-C(80) with respect to the relaxation rate of the carbons measured in their temperature dependence. Thus, we study the influence on the relaxation of the carbons and the dynamic behavior of these fullerenes in solution. Besides the diffusion dependence on the shape of the carbon cage, the relaxation behavior at lower temperatures is found to be dependent on the difference in chemical shift anisotropy within the carbon cage. This difference is originated from the changes of symmetry and results in polarization of electron density. Furthermore, the mobility of the carbons is influenced by their pyramidalization.

The endohedral cluster fullerenes Ih-Sc3N@C80, Ih-Y3N@C80, and Ih-Lu3N@C80 were investigated with respect to the strategy of an internal relaxation reagent by following the cluster size effects and the influence of f-electrons on the carbon relaxation. For endohedral nitride cluster fullerenes of Ih-C80 cage symmetry increased relaxation rates are observed. In general, the enlarged cage size increases the relaxation of the carbons. The encapsulated metal atoms give an additional dipole−dipole interaction to the relaxation rate of the carbon atoms depending on their magnetic character. For different metals the increased nitride cluster size is one reason for the observed stronger dipole−dipole interaction. In contrast, a higher shielding of a metal nucleus by its electron shell leads to a reduced magnetic effect. The negative charge on the cage increases the electron density, thus decreasing T1. In temperature-dependent studies, the diffusion is fast compared to the rotation of the molecule at higher tempe...

The superoxide anion radical, O2•−, induced C60 electropolymerization mechanism was refined by simultaneous cyclic voltammetric (CV) and vis-NIR spectroelectrochemical as well as mass spectrometric (MALDI-TOF) characterization of the one- and two-electron reduction products of C60 in the presence of O2 in a mixed organic solvent solution. The C60 polymer (C60-O) film was also investigated by Raman spectroscopy and imaged by atomic force microscopy (AFM) both at the early and advanced polymerization stage. While the spectroelectrochemical behavior of the C60/C60•− couple in the presence of O2 was similar to that in its absence, at more negative potentials corresponding to C602− and O2•− formation C602− participated in a chemical follow-up reaction resulting in a product lacking any diagnostic absorption band in the vis-NIR range. Although the main peak in the MS spectrum of the one-electron reduction product was that of C60 at m/z of 720, several additional peaks in the m/z range of 739−760 appeared, indic...

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 row of endohedral fullerenes is extended by a new type of sulfur-containing clusterfullerenes: the metal sulfide (M(2)S) has been stabilized within a fullerene cage for the first time. The new sulfur-containing clusterfullerenes M(2)S@C(82)-C(3v)(8) have been isolated for a variety of metals (M = Sc, Y, Dy, and Lu). The UV-vis-NIR, electrochemical, and FTIR spectroscopic characterization and extended DFT calculations point to a close similarity of the M(2)S@C(82) cage isomeric and electronic structure to that of the carbide clusterfullerenes M(2)C(2)@C(2n). The bonding in M(2)S@C(82) is studied in detail by molecular orbital analysis as well as with the use of quantum theory of atom-in-molecules (QTAIM) and electron localization function (ELF) approaches. The metal sulfide cluster formally transfers four electrons to the carbon cage, and metal-sulfur and metal-carbon cage bonds with a high degree of covalency are formed. Molecular dynamics simulations show that Sc(2)S cluster exhibits an almost free rotation around the C(3) axis of the carbon cage, resulting thus in a single line (45)Sc NMR spectrum.

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.

By direct arc synthesis of C60H2(C3H5N) using a modified Kratschmer−Huffman method, it is demonstrated for the first time that exohedral fullerenes with large side groups can be formed under the arc and reactive gas atmosphere conditions. The thus formed novel pyrrolino fullerene hydride was comprehensively characterized by UV−vis, infrared (IR), Raman and nuclear magnetic resonance (NMR) and studied by means of electrochemistry and in situ electron spin resonance/visible-near infrared (ESR/Vis-NIR) spectroelectrochemistry. The detailed NMR and absorption spectroscopic studies show C60H2(C3H5N) as the fullerene hydride with a pyrrolino ring attached on the vicinal position of two hydrogen atoms. This first cycloaddition adduct of C60H2 gives rise to an unusual reversible dimerization of its anion radicals and a loss of cage hydrogen atoms at the third electron transfer. The spectroelectrochemical study confirms the formation of a [C60H2(C3H5N)]− radical and the diamagnetic state of [C60H2(C3H5N)] 2−. This...