Syntheses and electronic properties of the nickel and palladium complexes of the octaethylporphyrin(M1)-(dihexylbithiophene)n-octaethylporphyrin(M2) system [OEP(M1)-(DHBTh)n-OEP(M2)] connected with the diacetylene linkage. A methodology for molecular design of the particular electronic structure

The palladium complexes of highly extended π-electronic conjugation system, octaethylporphyrin(Pd)-(dihexylbithiophene)_n-octaethylporphyrin(Pd) [OEP(Pd)-(DHBTh)_n-OEP(Pd), n=1-6], were synthesized, in which all the chromophores are connected with diacetylene linkage. The unsymmetrical derivatives of OEP(Ni)-DHBTh-OEP(Pd) were also successfully synthesized. Electronic properties of these symmetrical and unsymmetrical complexes were conclusively described, as compared with those of OEP(Ni)-(DHBTh)_n-OEP(Ni). Based on the structure elements, a methodical guiding principle for molecular design of the particular electronic structure will be proposed.     

Synthesis and structural and electronic properties of the diacetylene- and ethylene-groups connected octaethylporphyrin(Ni) tetramer

The tetramer of octaethylporphyrin nickel complex [OEP(Ni)], connected with diacetylene and ethylene linkages, was synthesized. Its structural and electronic properties were studied, proving that two constituents of the diacetylene-group connected OEP(Ni) dimer face to each other in s-cis conformation about the ethylene linkage but not so closely as to induce a transannular π-electronic interaction between them.     

Synthesis and properties of the octaethylporphyrin-dihexylbithiophene-pyridine system (OEP-DHBTh-Py) connected with diacetylene linkage. Proton-mediated and heat-driven spectral changes

Orientational isomers of the octaethylporphyrin-dihexylbithiophene-pyridine system (OEP-DHBTh-Py) connected with the diacetylene linkage were synthesized. The spectral measurements were performed under neutral and acidic conditions, clearly proving that the orientation of DHBTh affects not only the electronic structures of OEP-DHBTh-Py but also their proton-mediated spectral changes.     

Synthesis and electronic properties of hexylthiophene-octaethylporphyrin derivatives (HTh-OEP) connected with diacetylene linkage: substituent effect on the electronic structure of the extended HTh-OEP conjugation system

Octaethylporphyrin (OEP) was combined with 2-substituted 3-hexylthiophenes (HTh) by diacetylene linkage to afford the highly extended conjugation system (HTh-OEP). Their absorption spectral properties were examined, proving that the electronic structure of OEP is affected by the more electron-withdrawing substituents through the diacetylene linkage more dramatically. The substituent effect on the HTh-OEP conjugation system is much outstanding, as compared with that on the corresponding benzene system (Bzn-OEP).     

Synthesis and electronic properties of (oligo)phenothiazine-ethynyl-hydro-C60 dyads

Ethynyl bridged (oligo)phenothiazine-C₆₀ dyads 2 can be readily synthesized by addition of the corresponding (oligo)phenothiazinyl lithium acetylides 1 to C₆₀ followed by protonation with acetic acid. Cyclovoltammetric data of 1 and 2 reveal that the (oligo)phenothiazinyl moieties (donor) and the fullerene fragment (acceptor) are electronically decoupled in ground state, yet, each additional phenothiazine lowers the HOMO-LUMO gap by 100 mV. Upon UV excitation the phenothiazinyl fluorescence is considerably quenched, presumably as a consequence of a charge separation by an intramolecular photo-induced electron transfer from phenothiazine to fullerene.     

Synthesis, characterization and DFT calculations of new ethynyl-bridged C60 derivatives

A new series of soluble C₆₀ derivatives for organic electronic application has been synthesized by ethynylation reaction using different electron-donating and electron-withdrawing groups of varying length.     

Synthesis of new ferrocenyl derivatives and their use in the first cyclopropanation of fullerene C60 with ferrocenes

New ferrocenyl derivatives (a β-ketoester and a β-diester) were synthesised and linked to fullerene C₆₀, with the aim to elucidate factors involved in intramolecular electronic communication. These are the first examples of fullerene functionalised with ferrocenes via the cyclopropanation reaction. The resulting dyads were characterised.     

Synthesis and photophysical characterization of a titanium(IV) phthalocyanine-C60 supramolecular dyad

An axially substituted titanium(IV) phthalocyanine-fullerene donor-acceptor supramolecular dyad has been prepared by two different approaches, one of them representing a convenient convergent strategy. The dyad system exhibits photoinduced electron transfer upon irradiation with visible light to produce a microsecond lived charge separated state.     

Synthesis and properties of unsymmetrically extended π-electronic conjugation system of octaethylporphyrin(Ni)-dihexybithiophene-octaethylporphyrin(Pd) connected with diacetylene linkage

Orientational isomers of the diacetylene-group connected dihexybithiophene (DHBTh) derivatives have been synthesized, in which the different octaethylporphyrin (OEP(M); M=Ni or Pd) rings are attached at the ends. Reflecting the unsymmetrical structural feature, the peculiar electronic properties of the extended OEP(Ni)-DHBTh-OEP(Pd) system were observed.     

Synthesis and properties of thermally cross-linkable main-chain azobenzene polymers containing diacetylene moieties

A series of main chain azobenzene polymers containing diacetylene moieties with different lengths of the spacer {-[CC-CH₂-O-C₆H₄-OCO-(CH₂)_m-O-C₆H₄-NN-C₆H₄-O-(CH₂)_m-OCO-C₆H₄-O-CH₂-CC]_n-, where m = 3, 6, 11} were synthesized by oxidative coupling polymerization. These polymers had molecular weights of 17,600-68,600 and polydispersity indices of 1.2-1.8 as determined by gel permeation chromatography using polystyrene as a standard. Their structures and properties were characterized and evaluated with NMR, FT-IR, X-ray diffraction (XRD), thermogravimetry (TG), differential scanning calorimetry (DSC) and nonlinear optical (NLO) analyses. All the polymers could be cross-linked at the elevated temperatures due to the polymerization reactions of the diacetylene groups in the polymer backbone, and the cross-linked polymers showed dramatically modified properties, such as thermal stability and solvent resistance. The third-order nonlinear susceptibilities of the cross-linked polymers were evaluated by means of the Z-scan technique and calculated to be 3.60 × 10⁻⁹, 2.73 × 10⁻⁹, 2.28 × 10⁻⁹ esu, respectively, whereas the un-cross-linked polymers showed no obvious NLO property.     

Local density functional study of the structural and electronic properties of C60 and XC60 (X=K, Rb, Cs)

Results of first principles local density total energy and atomic force calculations carried out for free C₆₀ and XC₆₀ (X=K, Rb, Cs) molecular clusters are reported. The optimization of the geometry results in the bond lengths between adjacent carbon atoms being 1.387 and 1.445 Å, which are in very good agreement with the latest X-ray diffraction values. Energy levels, charge distributions, and wavefunction characteristics are obtained and discussed. The results for C₆₀ are in very good agreement with recently measured photoemission energy distribution curves (EDC) for the valence band states. The highest occupied molecular orbitals (HOMO) are found to be fully occupied H_u states and are 1.7 eV below the lowest unoccupied molecular orbitals (LUMO) which are of T_1u symmetry. Similar results obtained for the XC₆₀ clusters show that rigid-band-like behavior is found in the electronic structures after putting an alkali atom at the center of a C₆₀ ball. In each case, the alkali atom is almost fully ionized with the transferred electron distributed over the surface shell of C₆₀; the center region of the ball has very low charge density.     

First syntheses and electronic properties of (oligo)phenothiazine-C60 dyads

(Oligo)phenothiazine-C₆₀ dyads 3 can be readily synthesized by a three-component condensation-cycloaddition of the corresponding (oligo)phenothiazinyl carbaldehydes 1, N-hexyl glycine (2), and C₆₀. Cyclic voltammetry of 3 and reference compounds 4 shows that the phenothiazinyl moiety (donor) and the fullerene fragment (acceptor) are electronically decoupled in ground state. However, upon UV excitation the phenothiazinyl fluorescence is considerably quenched, presumably as a consequence of a charge separation by an intramolecular photo-induced electron transfer from phenothiazine to fullerene.     

Semiempirical molecular dynamics studies of C60/C70 fullerene oxides: C60O, C60O2 and C70O

The spectral analysis indicates that all isomers of C₆₀O, C₇₀O and C₆₀O₂ have an epoxide-like structure (an oxygen atom bridging across a C–C bond). According to the geometrical structure analysis, there are two isomers of fullerene monoxide C₆₀O (the 5,6 bond and the 6,6 bond), eight isomers of fullerene monoxide C₇₀O and eight isomers of fullerene dioxide C₆₀O₂. In order to simulate the real reaction conditions at 300 K, the calculation of the different isomers of C₆₀O, C₆₀O₂ and C₇₀O fullerene oxides was carried out using the semiempirical molecular dynamics method with two different approaches: (a) consideration of the geometries and thermodynamic stabilities, and (b) consideration of the ozonolysis mechanism. According to the semiempirical molecular dynamic calculation analysis, the probable product of this ozonolysis reaction is C₆₀O with oxygen bridging over the 6–6 bond (C_2v). The most probable product in this reaction contains oxygen bridging across in the upper part of C₇₀ (6–6 bond in C₇₀O-2 or C₇₀O-4) an epoxide-like structure. C₆₀O₂-1, C₆₀O₂-3 and C₆₀O₂-5 are the most probable products for the fullerene dioxides. All of these reaction products are consistent with the experimental results. It is confirmed that the calculation results with the semiempirical molecular dynamics method are close to the experimental work. The semiempirical molecular dynamics method can offer both the reaction temperature effect by molecular dynamics and electronic structure, dipole moment by quantum chemistry calculation.     

Structure and electronic properties of quinone dimers connected with acetylene and diacetylene linkages

Quinone dimers connected with acetylene (QAQ) and diacetylene linkages (QAAQ) have been synthesized and their structure and electronic properties studied. X-ray analysis, DFT calculations, and UV-vis measurements showed that, unlike directly connected quinone dimers (QQ), they had planar and thus efficiently extended π conjugation systems. The respective reduction potentials of QAQ and QAAQ were considerably raised, and QAQ thereby behaved as a mild oxidizing agent.     

Synthesis and characterization of a new ethynyl-bridged C60 derivative bearing a diketopyrrolopyrrole moiety

A new soluble C₆₀ derivative bearing a diketopyrrolopyrrole (DPP) moiety has been synthesized by ethynylation reaction. Characterization by UV-visible spectrophotometry and cyclic voltammetry has been performed in order to study the influence of the DPP moiety on electronic and optical properties of the fullerene. Moreover, DFT calculations have been conducted on the derivative and its precursor in order to correlate the orbital geometry with experimental data.     

Stability of neutral and charged Si50 cage and stacked structure and in comparison with Si60 structures

We have performed calculations on the fullerene cage and stacked structures of neutral and ionic Si₅₀ cluster by full-potential linear-muffin-tin-orbital molecular-dynamics (FP-LMTO-MD) method. It is found that the neutral and charged fullerene cages relax into distorted structures resembling puckered balls. Their electronic structures are remarkably similar besides their geometrical structures. However, the relaxed cages are still not so stable as the stacked structure built from tricapped trigonal prism. By comparison, for the fullerene cages and stacked structures of neutral and ionic Si₆₀ cluster, similar characteristics are found.     

High-temperature and photochemical syntheses of C60 and C70 fullerene derivatives with linear perfluoroalkyl chains

New experimental results on perfluoroalkylation of C₆₀ and C₇₀ with the use of R_fI (R_f = CF₃, C₂F₅, n-C₃F₇, n-C₄F₉, and n-C₆F₁₃), along with a critical overview of the existing synthetic methods, are presented. For the selected new fullerene (R_f)_n compounds we report spectroscopic, electrochemical and structural data, including improved crystallographic data for the isomers of C₇₀(C₂F₅)₁₀ and C₆₀(C₂F₅)₁₀, and the first X-ray structural data for the dodecasubstituted perfluoethylated C₇₀ fullerene, C₇₀(C₂F₅)₁₂, which possesses unprecedented addition pattern.     

Radical scavenging efficiency of different fullerenes C60-C70 and fullerene soot

This investigation was undertaken to determine the antioxidant activity of a range of fullerenes C₆₀ and C₇₀ in order to rank them according to their comparative efficiency. The model reaction of initiated (2,2′- azobisisobutyronitrile, AIBN) cumene oxidation was used to determine rate constants for addition of radicals to fullerenes. Measurements of oxidation rates in the presence of different fullerenes showed that the antioxidant activity as well as the mechanism and mode of inhibition were different for fullerenes C₆₀ and C₇₀ and fullerene soot. All fullerenes - C₆₀ of gold grade, C₆₀/C₇₀ (93/7, mix 1), C₆₀/C₇₀ (80 ± 5/20 ± 5, mix 2) and C₇₀ operated as alkyl radical acceptora, whereas fullerene soot surprisingly retarded the model reaction by a dual mode similar to that for the fullerenes and with an induction period like many of the sterically hindered phenolic and amine antioxidants. For the C₆₀ and C₇₀ the oxidation rates were found to depend linearly on the reciprocal square root of the concentration over a sufficiently wide range thereby fitting the mechanism for the addition of cumylalkyl radicals to the fullerene core. This is consistent with literature data on the more ready and rapid addition of alkyl and alkoxy radicals to the fullerenes compared with peroxy radicals. Rate constants for the addition of cumyl radicals to the fullerenes were determined to be k_(333K) = (1.9 ± 0.2) × 10⁸ (C₆₀); (2.3 ± 0.2) × 10⁸ (C₆₀/C₇₀, mix 1); (2.7 ± 0.2) × 10⁸ (C₆₀/C₇₀, mix 2); (3.0 ± 0.3) × 10⁸ (C₇₀), M⁻¹ s⁻¹. The increasing C₇₀ constituent in the fullerenes leads to a corresponding increase in the rate constant.The fullerene soot inhibits the model reaction according to the mechanism of trapping of peroxy radicals; the oxidation proceeds with a pronounced induction period and kinetic curves are linear in semi-logarithmic coordinates.For the first time the effective concentration of inhibiting centres and inhibition rate constants for the fullerene soot have been determined to be fn[C₆₀−soot] = (2.0 ± 0.1) × 10⁻⁴ mol g⁻¹ and k_inh = (6.5 ± 1.5) × 10³ M⁻¹ s⁻¹ respectively.The kinetic data obtained specify the level of antioxidant activity for the commercial fullerenes and scope for their rational use in different composites. The results may be helpful for designing an optimal profile of composites containing fullerenes.     

Synthesis and properties of 1,1′-bis(diacetylene-group) connected ferrocene-thiophene derivative: a cooperatively functional behavior of diacetylene-group connected constituents

An extended π-electronic conjugation system of 1,1′-bis(diacetylene-group) connected ferrocene-thiophene derivative has been synthesized, with our integrated reaction between the corresponding TMS-protected acetylenes in one-pot. Its electronic properties have been examined, suggesting a cooperatively functional behavior of the diacetylene-group connected constituents.     

Synthesis of C60 derivatives for photoaffinity labeling

In order to study the interaction of fullerenes with biological molecules, a novel photoaffinity labeling agent derived from C₆₀ was designed and synthesized. As photosensitive functional groups, azide group, and aziridine group are utilized. A convenient synthetic route via fulleropyrrolidine 2 was employed to obtain compounds labeling agents 5 and 9.