Negative differential resistance and memory effect in diodes based on 1,4-dibenzyl C60 and zinc phthalocyanine doped polystyrene hybrid material

Negative differential resistance (NDR) and memory effect were observed in diodes based on 1,4-dibenzyl C60 (DBC) and zinc phthalocyanine doped polystyrene hybrid material. Certain negative starting sweeping voltages led to a reproducible NDR, making the hybrid material a promising candidate in memory devices. It was found that the introduction of DBC enhanced the ON/OFF current ratio and significantly improved the memory stability. The ON/OFF current ratio was up to 2 orders of magnitude. The write-read-erase-reread cycles were more than 106, and the retention time reached 10,000 s without current degradation.     

A new terpyridine tethered polythiophene: Electrosynthesis and characterization

A novel polythiophene bearing a pendant terpyridine moiety has been synthesized by electrochemical polymerization of a new thiophene monomer, namely 4′‐(2,2′:5′,2″‐terthien‐3′‐ethynyl)‐2,2′:6′,2″‐terpyridine (TAT). The insertion of a conjugated ethynyl spacer between the terthiophene and the terpyridine fragments provides for an effective extension of the delocalization of electrons within the structural unit and the polymer as a whole. The synthesis and characterization of the relevant monomer, the electrosynthesis of the corresponding polymer and its electrochemical, UV–visible spectroelectrochemical and IR characterization are described. Finally, a comparison between the electrochemical, spectroscopic, and spectroelectrochemical properties of PTAT and the analogue, saturated‐spacer PTTT (TTT = 4′‐[(2,2′:5′,2″‐terthien‐3′‐yl)methoxy]‐2,2′:6′,2″‐terpyridine) polymer is discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of star polyfluorenes with a C60 core

C60‐cored star polyfluorenes were synthesized and fully characterized. A high yield (81%) hexakisaddition of C60 was developed by using Prato reaction and bulky fluorene addends. Suzuki polycondensation of the hexakisadducts of C60 carrying six 2‐bromofluorene addends and AB‐type monomer (2‐bromo‐9,9‐dioctylfluorenyl‐4,4,5,5‐tetramethyl‐ [1,3,2]‐dioxaborane) with Pd(PPh₃)₄ as the catalyst precursor afforded the desired C60‐cored star polyfluorenes. Their three‐dimensional structure can effectively reduce the aggregation of the polyfluorene chains. Annealing studies indicated that the C60‐cored star polyfluorenes are of good color stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4696–4706, 2007     

Synthesis and characterization of tetrakis-silylated C60 isomers

A photochemical reaction of C(60) with disilane in a 2:3 ratio affords the isomer mixture of the tetrakis-adduct of C(60)((t)BuPh(2)Si)(4) as the major product. The use of a three-stage HPLC separation system isolated three of their isomers. Their structural assignments were based on FAB mass, UV-vis, NMR, and cyclic voltammetry (CV) measurements. The CV analysis showed that the terakis-adduct has lower oxidation and higher reduction potentials than the bis-adduct C(60)((t)BuPh(2)Si)(2) and the parent C(60).     

Preparation and crystallographic characterization of C60Cl24

C60Cl24 has been synthesized by the chlorination of C60 with VCl4 or C60Br24 with SbCl5; the X-ray single crystal structure of C60Cl24.2Br2 confirmed the molecular T(h) symmetry in good agreement with the IR data and theoretical calculations.     

Electrosynthesis and thermal characterization of basic copper carbonate nanoparticles

The present study concerns the electrochemical synthesis of basic copper carbonate nanoparticles by oxidation of metallic copper on the anode in an aqueous bicarbonate solution. This simple and one-step preparation can be considered as green synthesis. The scanning electron microscopy (SEM) analysis indicates that average particle size of the product is in the range of about 70 nm. On the other hand, basic copper carbonate micro-powder has been prepared, by mixing solutions of copper(II) sulphate and sodiu bicarbonate. The SEM analysis showed that the size of particles prepared in the same way is in the range of about 1 μm. In another part of this study, the thermal decomposition of micro and nanoparticles of copper carbonate produced by various methods was studied in air using TG-DTA techniques. The results of thermal study show that the decomposition of both samples occurs in single step. Also, the TG-DTA analysis of the nanoparticles indicates that the main thermal degradation occurs in the temperature range of 245–315°C. However, microparticles of Cu(OH)₂ · CuCO₃ decomposed endothermally in the temperature range of 230–330°C.      

Rotational dynamics and polymerization of C60 in C60-cubane crystals: a molecular dynamics study

We report classical and tight-binding molecular dynamics simulations of the C(60) fullerene and cubane molecular crystal in order to investigate the intermolecular dynamics and polymerization processes. Our results show that, for 200 and 400 K, cubane molecules remain basically fixed, presenting only thermal vibrations, while C(60) fullerenes show rotational motions. Fullerenes perform "free" rotational motions at short times (approximately < 1 ps), small amplitude hindered rotational motions (librations) at intermediate times, and rotational diffusive dynamics at long times (approximately > 10 ps). The mechanisms underlying these dynamics are presented. Random copolymerizations among cubanes and fullerenes were observed when temperature is increased, leading to the formation of a disordered structure. Changes in the radial distribution function and electronic density of states indicate the coexistence of amorphous and crystalline phases. The different conformational phases that cubanes and fullerenes undergo during the copolymerization process are discussed.     

Solvent-dependence of KI Mediated Electrosynthesis of Imidazo[1,2-a]pyridines

Iodized salts are widely used as mediators to promote C—H functionalization. Solvents and additives have been described as significant roles in these reactions. However, the further electrochemical investigations have rarely been reported. Herein, a KI mediated electrochemical annulation between acetophenones and 2-amniopyridines was developed. We revealed the effect of acids and solvents by cyclic voltammetry(CV), differential pulse voltammetry(DPV), and square wave voltammetry(SWV). The oxidation of 2-aminopyridine is inhibited at the potential window with the addition of strong acids, and the lowest oxidation potential difference of KI was obtained by utilizing EtOH as solvent. The experimental studies also show that the mixture solvent of EtOH/DMSO(9/1, volume ratio) facilitates the electrochemical cyclization due to the solubility improvement of KI. CF₃SO₃H has been screened as the optimal acid. A range of Imidazo[1,2-a]- pyridines have been synthesized in yields of 42% to 96%. Electrochemical investigations present that the KI mediated electro- chemical reaction is probably solvent-dependence.     

Tube and cage C(60)H(60): a comparison with C(60)F(60)

Tube C(60)H(60) (5) with fused five-membered rings is more stable than the cage isomer (1) with isolated five-membered rings. Introduction of endo C-H bonds into structure 5 results in further stabilization, but the most stable tube structure with four endo C-H bonds (7) is higher in energy than the most stable cage structure with ten endo C-H bonds (3) by 74.2 kcal/mol. A comprehensive comparison of C(60)H(60) with C(60)F(60) has been made.     

Electrosynthesis and characterization of aminomethyl functionalized PEDOT with electrochromic property

We herein report the electrosynthesis of an aminomethyl functionalized poly(3,4-ethylenedioxythiophene)(PEDOT) derivative, poly(2'-aminomethyl-3,4-ethylenedioxythiophene)(PEDOT-Me NH2), in CH2Cl2-Bu4NPF6(0.1 mol·L-1) system containing 2% boron trifluoride diethyl etherate(BFEE). The electrochemical behavior, structure characterization, thermal properties and surface morphology of this novel polymer were systematically investigated by cyclic voltammetry(CV), Fourier-transform infrared spectroscopy(FTIR), thermogravimetry(TG) and scanning electron microscopy(SEM), respectively. Electrochemistry results demonstrated that PEDOT-Me NH2 film displayed good redox properties and high electrochemical stability. Besides, PEDOT-Me NH2 films exhibited the electrochromic nature with obvious color changing from purple in the reduced form to blue upon oxidation. By further investigation, kinetic studies revealed that PEDOT-Me NH2 film had decent contrast ratio(41.8%), favorable coloration efficiency(152.1 cm2·C-1), low switching voltages and moderate response time(2.4 s). Satisfactory results implied that the obtained PEDOT-Me NH2 film is a promising optoelectronic material and holds promise for electrochromic devices and display applications.     

Formation of singly bonded PhCH2C60-C60CH2Ph dimers from 1,2-(PhCH2)HC60 via electroreductive C60-H activation

Singly bonded PhCH(2)C(60)-C(60)CH(2)Ph dimers are generated via controlled-potential bulk electroreduction and electrooxidation of 1,2-(PhCH(2))HC(60). The reaction mixture was purified by HPLC, and the isolated fraction was characterized with single-crystal X-ray diffractions, (1)H and (13)NMR, MS, elemental analysis, and cyclic voltammetry. It was shown that the fraction consists of two HPLC-inseparable PhCH(2)C(60)-C(60)CH(2)Ph regioisomers, which are assigned as the meso and racemic regioisomers. The bulk electrolysis processes for the formation of the dimers were followed by in situ cyclic voltammetry and were further corroborated with an in situ voltammetric titration of 1,2-(PhCH(2))HC(60) with tetra-n-butylammonium hydroxide (TBAOH), on the basis of which a reaction mechanism is proposed.     

Synthesis and characterization of difluoromethylene-homo[60]fullerene, C60(CF2)

Refluxing of the o-DCB solution of C60 with CF2ClCOONa and 18-crown-6 leads to formation of C60(CF2)n (n = 1-3); the monoadduct C60(CF2) has been found to consist of the main [6,6]- and minor [5,6]-isomers, both having an open structure.     

Raman characterization of C60 salts electroformed in aqueous media

Electrochemical intercalation of C₆₀ films from aqueous LiOH, KOH, NaOH, RbOH and CsOH solutions was studied by electrochemical methods and Raman spectroscopy. The intercalation of these alkali metals cations gives rise to reduction peaks at different applied potentials depending on the chemical nature of the cation used. Reduction of the C₆₀ films was observed to rather different extents depending on the composition of the working solution. Electrochemical and Raman experiments show that K⁺ and Cs⁺ ions form the most stables and active salts, while Li⁺, Na⁺ and Rb⁺ are not significantly intercalated. Furthermore, Raman characterization of the K⁺ and Cs⁺ doped films leads to the identification of the its main components, namely the K₂C₆₀ and CsC₆₀ species.     

Theoretical studies of C60/C70 fullerene derivatives: C60O and C70O

A semiempirical (AM1) calculation on the structures and stabilities of isomers of the fullerene derivatives C₆₀O and C₇₀O is carried out. The ozonolysis reaction mechanism and the thermodynamics of the compounds are studied. The two isomers of C₆₀O (56 bond and 66 bond) formed by an oxygen atom bridging across a C-C bond have an epoxide-like or an annulene-like structure. According to the ozonolysis reaction mechanism and kinetic factor analysis, the possible products of this ozonolysis reaction are C₆₀O with oxygen bridging over the 66 bond (C_2v) as an epoxide-like isomer and that with oxygen bridging over the 56 bond (C_s) as an annulene-like isomer. Further, the sixteen isomers of C₇₀O (both epoxide-like and annulene-like structures) have been studied with respect to the same reaction mechanism. The most possible product in this ozonolysis reaction contains oxygen bridging across in the upper part (66 bond in C₇₀O-2 or C₇₀O-4) as an epoxide-like structure. The other possible product is C₇₀O-8 (annulene-like structure), in which oxygen bridges across an broken equatorial CC bond in C₇₀ (D_5h). The vibrational frequency analysis and the electronic structure of the selected C₆₀O and C₇₀O isomers are generated for experimental characterisation. The experimental results indicate that C₆₀O and C₇₀O may decompose into the odd number fullerenes C₅₉ and C₆₉. We therefore studied the structures of C₅₉ and C₆₉ also.     

The former "C60F16" is actually a double-caged adduct: (C60F16)(C60)

X-ray diffraction study of the substance originally believed to be C(60)F(16) reveals a double-caged structure, (C(60)F(16))(C(60)); MALDI mass spectra, 19F NMR spectral data and reasons for stability are discussed.     

Synthesis and characterization of C60/polyaniline composites from interfacial polymerization

C₆₀/polyaniline (PANI) nanocomposites have been synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in the presence of C₆₀ by using an interfacial reaction. When compared with the pure PANI nanofibers from the similar process, the diameter of the obtained C₆₀/PANI nanofibers was increased because of the encapsulation of C₆₀ into PANI during aniline polymerization, which resulted from the charge‐transfer interactions between C₆₀ and aniline fragment in PANI. In addition, the resulting C₆₀/PANI nanocomposites synthesized from the low initial C₆₀/aniline molar ratio (less than 1:25) showed the homogenous morphology composed of fiber network structures, which has an electrical conductivity as high as 1.1 × 10^?4 S/cm. However, the C₆₀/PANI nanocomposites from the higher initial C₆₀/aniline molar ratio (more than 1:15) showed the nonuniformly distributed morphology, and the electrical conductivity was decreased to 3.5 × 10^?5 S/cm. Moreover, the C₆₀/PANI nanocomposites from the interfacial reaction showed a higher value of electrical conductivity than the mechanically mixed C₆₀/PANI blends with the same C₆₀ content, because of the more evenly distributed microstructures. FTIR, UV–vis, and CV data confirmed the presence of C₆₀ and the significant charge‐transfer interactions in the resultant nanocomposites, which was responsible for the morphology development of the C₆₀/PANI and the variation of the electrical conductivity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

A (13)C INADEQUATE and HF-GIAO study of C(60)H(2) and C(60)H(6) identification of ring currents in a 1,2-dihydrofullerene

The hydrofullerenes C(60)H(2) (1) and C(60)H(6) (2) have been prepared in (13)C-enriched form and 2D INADEQUATE NMR spectra were measured. These spectra have provided unambiguous (13)C assignments for 2, and nearly unambiguous assignments for 1. In both cases, the most downfield resonances are immediately adjacent to the sp(3) carbons, despite the fact that these carbons are the least pyramidalized carbons in the molecule. Typically, (13)C chemical shifts move downfield with increasing pyramidalization (THETA(p)), but in these systems there is no strong correlation between THETA(p) and delta. HF-GIAO calculations are able to predict the chemical shifts, but provide little chemical insight into the origin of these chemical shifts. London theory reveals a significant paramagnetic ring current in 1, a feature that helps explain the (1)H shifts in these compounds and may contribute to the (13)C chemical shifts as well.     

Ferric Perchlorate-Mediated Synthesis of 1,2-Fullerenols C(60)(OCOR)(OH)

1,2-Fullerenols C(60)(OCOR)(OH) have been facilely synthesized via the one-step reaction of [60]fullerene with acid chlorides promoted by ferric perchlorate. A possible reaction mechanism for the product formation is proposed.