Ruifang Cai

The synthesis and characterization of C60 chemically modified poly(N-vinylcarbazole)

Addition of C60 moiety, a powerful electron acceptor to poly(N-vinylcarbazole) (PVK) by chemical reaction modifies considerably the physical and chemical properties of PVK. The characterization techniques employed are UV-visible, IR, DSC, TGA, ESR, 13C-NMR spectroscopy, scanning electron microscopy, XRD, and cyclic voltammetry. The fullerenated PVK, which has a visibly earthy yellow cast when compared with the unreacted polymer, has a new structure in the UV-vis absorption spectrum with the active range extending from about 280 to 870 nm, its apparent temperature sensitivity is intriguing, and an unusual temperature dependence for the ESR spectrum is observed. Considerable difference of electronic structure between pure PVK and C60-PVK copolymer is indicated. The thermal stability and oxidation-reduction activation of pure PVK are enhanced by C60-chemical modification.

Preparation and structural characterization of a star-shaped C60HxBTPVKx copolymer

Abstract A highly soluble star-shaped C 60 H x BTPVK x copolymer, which has significantly different spectroscopic properties from both free C 60 and n -butyl-terminated poly( N -vinylcarbazole)[BTPVK], was prepared in heterogeneous medium. 13 C NMR results provided a strong convincing evidence for the covalent attachment of BTPVK arms onto the C 60 core, a versatile tecton for dendrimer chemistry [Camps, X., Schonberger, H. and Hirsch, A., Chem. Eur. J ., 1997, 3 , 561]. The characterization techniques employed are UV-VIS, FTIR, TGA, ESR, XRD and 13 C NMR spectroscopy.

Insertion of carbodiimide into the LnN σ-bond of organolanthanide complexes. Synthesis and characterization of organolanthanide guanidinates (C5H5)2Ln[iPrNC(NiPr2)∴NiPr] (Ln=Yb, Dy, Gd)

Abstract The synthesis and structures of three new lanthanide complexes incorporating tetra-substituted guanidinate ligand [iPrN∴C(NiPr2)∴NiPr] are described. Treatment of Cp2LnNiPr2(THF) (Ln=Yb, Dy, Gd) with N,N′-di-isopropyl-carbodiimide results in mono-insertion of carbodiimide into the LnN σ-bond to yield Cp2Ln[iPrN∴C(NiPr2)∴NiPr] (Ln=Yb(1), Dy(2), Gd(3)), providing an efficient method for the synthesis of organolanthanide guanidinate complexes. It was found that an excess of N,N′-di-isopropyl-carbodiimide did not affect the nature of the final product. Complexes 1–3 were characterized by elemental analysis, IR and mass spectroscopies. Complexes 1 and 2 were determined by the X-ray single crystal diffraction analysis.

Anionic copolymerization of [60]fullerene with styrene initiated by sodium naphthalene

The novel C 60 -styrene copolymers with different C 60 contents were prepared in sodium naphthalene-initiated anionic polymerization reactions. Like the pure polystyrene, these copolymers exhibited the high solvency in many common organic solvents, even for the copolymer with high C 60 content. In the polymerization process of C 60 with styrene an important side reaction, i.e., reaction of C 60 with sodium naphthalene, would occur simultaneously, whereas crosslinking reaction may be negligible. 13 C-NMR results provided an evidence that C 60 was incorporated covalently into the polystyrene backbone. In contrast to pure polystyrene, the TGA spectrum of copolymer containing ∼ 13% of C 60 shows two plateaus. The polystyrene chain segment in copolymer decomposed first at 300-400°C. Then the fullerene units reptured from the corresponding polystyrene fragments attached directly to the C 60 cores at 500-638°C. XRD evidence indicates that the degree of order of polymers increases with the fullerene content increased in terms of crystallography. Incorporation of C 60 into polystyrene results in the formation of new crystal gratings or crystallization phases. In addition, it was also found that [60]fullerene and its polyanion salts [C 60 n (M + ) n , M = Li, Na] cannot be used to initiate the anionic polymerization of some monomers such as acrylonitrile and styrene, etc.

A novel bonding mode of tetrazolate ligand to a metal: synthesis and structural characterization of 5-phenyltetrazolate organolanthanide complexes: [{(C5H4Me)(C5H5)LnTz}2][{(C5H4Me)2LnTz}2] (Ln=Dy, Gd) and [(C5H4Me)2LnTz)]2 (Ln=Yb, Er)

Reaction of (C 5 H 4 Me) 3 Ln and TzH (5-phenyl-1H-tetrazole) in THF affords complexes [(C 5 H 4 Me) 2 LnTz] 2 [Ln=Yb ( 1 ), Er ( 2 )]. 1 crystallized in the space group C 2/ c , with unit cell dimensions a =25.596(2), b =8.342(1), c =21.573(2) A, β =129.322(9)°. V =3563.5(8) A 3 and Z =8 for D c =1.776 g cm −3 . Least-squares refinement of the model based on 2700 reflections converged to a final R =0.031. The molecule is centrosymmetric dimer in which each ytterbium atom is coordinated by two methylcyclopentadienyl groups and three nitrogen atoms of the bridging Tz ligands to form a distorted trigonal-bipyramidal geometry. When there is a small amount of (C 5 H 4 Me) 2 Ln(C 5 H 5 ) in (C 5 H 4 Me) 3 Ln, the 1:1 complexes [{(C 5 H 4 Me)(C 5 H 5 )LnTz} 2 ][{(C 5 H 4 Me) 2 LnTz} 2 ] (Ln=Dy ( 3 ), Gd ( 4 )) were obtained in crystalline form. 3 and 4 crystallize as isomorphous crystals of space group P 1 with the following unit cell parameters ( 3 / 4 ): a =9.374(2)/9.420(4), b =13.048(2)/13.215(4), c =16.542(4)/16.677(5) A, a =86.95(2)/87.24(2), β =74.61(1)/74.50(3), γ =77.31(1)/77.08(3)°, Y =1903(1)/1950(1) A 3 , Z =2, D c =1.602/1.545 g cm −3 , R =0.046/0.051. Crystallographic data for 3 and 4 show that there are two disconnected structural units [(C 5 H 4 Me)(C 5 H 5 )Ln( μ - η 1 : η 2 -Tz)] 2 and [(C 5 H 4 Me) 2 Ln( μ - η 1 : η 2 -Tz)] 2 , crystallizing in one asymmetrical unit, each of which is tetrazolate-bridged dimer and has an inversion center. The bridging unit Ln 2 N 6 is planar. All three structures reveal an unusual bonding mode of the tetrazolate ligand, in which the tetrazolate group acts as both a bridging and chelating ligand, with the nitrogen atoms at 1, 2 and 3-position taking part in bonding.

Synthesis and characterization of a soluble and starlike C60(CH3)x(PAN)x copolymer

Abstract A novel starlike C 60 (CH 3 ) x (PAN) x copolymer was prepared by reaction of the living n Butyl-terminated polyacrylonitrile (PAN) with C 60 , followed by a capping reaction with methyl iodine. Multiple PAN arms are attached to the C 60 core. The characterization techniques employed are UV-vis, FT-IR, 13 C NMR, TGA, XRD, ESR and SEM. This starlike polymer has a visibly yellow cast when compared with the unfunctionalized polymer. The chemical and physical properties of this polymer depend largely on the concentrations of the fullerene covalently bound to the polymer matrix and on the chain-length of PAN units attached to a C 60 center. A qualitative comparison of the submicro-morphological structures of the copolymer and the pure n Butyl-terminated poly-acrylonitrile is given.

Synthesis and characterization of soluble C60-chemically modified poly(p-bromostyrene)

Addition of bulky C60 moiety, a powerful electron acceptor (EA = 2.6–2.8 eV), to the poly(p-bromostyrene)(PBS) by a novel organometallic reaction considerably changes the chemical and physical properties of this polymer. The product obtained is a “charm-bracelet” non-crosslinked brownish yellow polymer which is easily soluble in many common organic solvents, and has a single glass transition temperature [134.0°C vs. 83.2°C for poly(p-bromostyrene)], this being congruent with its chemical structure. Covalent attachment of C60 to the brominated polystyrene backbone is confirmed by a variety of techniques such as UV-VIS, FT-IR, TGA, DSC, SEM, ESR, GPC, and 13C-NMR. The results show that both the stereo-electronic effect and the steric hindrance of C60 have an important influence on the structure and physical properties of polymer.

Photoconductivity and paramagnetism of fullerene chemically modified polymers

Addition of the C60 moiety, a powerful electron acceptor, to iodinated poly(N-vinylcarbazole) (PVKI) by chemical reaction modifies considerably the photoconductive property of PVKI. The photoinduced discharge rates for pure PVK, PVKI, C60-chemically modified PVKI (C60-PVKI copolymer), and C60-doped PVKI (a simple mixture of the component) under the same experimental conditions are found in the following order: C60-PVKI copolymer > C60-doped PVKI > PVKI > PVK. The fullerenated PVKI has a visibly brownish yellow cast when compared with the unreacted polymer. The UV-vis absorption spectrum in which the main bands occur at 220, 230, 252, 268, 300, 332, and 346 nm extends the active range from about 300 to 860 nm. Also, its apparent temperature sensitivity is very intriguing, and an unusual temperature dependence for the ESR spectrum is observed. The photoconductive performance of the fullerenated polymer is closely related to its paramagnetism. A considerable difference of electronic structure between pure PVKI and the C60-PVKI copolymer is indicated.

Solid-state magnetic resonance study of KC60(THF)x

Abstract Solid-state ESR and 13 C NMR spectra indicate that two electronic states of C 60 − exist in KC 60 (THF) x (0 x 2 A : (arising from the C 60 − … K + loose ion-pair) and 2 E (arising from the C 60 − K + (THF) tight ion-pair) states, originating from the splitting of the 2 T 1 u state induced by Jahn-Teller distortion.

Synthesis and characterization of photoconductive C60–N-vinylcarbazole copolymers

Soluble C60–N-vinylcarbazole copolymers with different C60 contents were synthesized in lithium naphthalene-initiated anionic polymerization reactions. 13C nuclear magnetic resonance (NMR) results provided strong evidence for the covalent attachment of poly(N-vinylcarbazole; PVK) units to the C60 cores. The chemical shifts located at 142.16, 143.21, 144.70, 145.61, 146.65, 147.09, 149.08 and 170.28 p.p.m. in the 13C NMR spectrum of the copolymer are assigned to the unsaturated carbon signals of the substituted C60 cage. Its ultraviolet–visible absorption spectrum tends to move to the longer wavelength compared with those of the N-vinylcarbazole (NVC) monomer and PVK, and the peak range also extended from about 350 to 640 nm due to “charge-transfer” interaction between C60 and N-ethylcarbazole units. X-ray diffraction evidence suggests that the structure of the resultant copolymer might be a layered structure. Like the C60 chemically modified PVK, this material also exhibits good photoconductivity and temperature sensitivity. An unusual temperature dependence of the ESR spectrum is observed. In addition, it is also found that both [60] fullerene polyanion salts [(Cn-60) M+n, M=Li, Na, K] and fullerene itself are unable to initiate the polymerization of such monomers as N-vinylcarbazole, styrene and acrylonitrile, etc.