Twisted intramolecular motion arrested in aggregated state emission and the nonlinear optical properties of pyrene pyrazoline derivatives.

Heterocyclic pyrene pyrazoline moieties containing similar structures but with differences in thiophene (PPT), furan (PPF) and pyridine (PPP) substitutions at the terminal molecules were synthesized. Their aggregation behaviour in THF-water mixtures was investigated and results demonstrated that PPT and PPP exhibited aggregation-induced emission (AIE), whereas PPF exhibited aggregation-induced blue-shifted emission (AIBSE). PPT and PPP provided red-shifted emission, while PPF had observed blue-shifted emission at high water fractions of 70-90%, confirming that aggregation effects played a major role in the molecular structure. Two emission peaks from locally excited and twisted intramolecular charge transfer confirmed the twisted nature from the dihedral angle values of the free reorganized molecules that were completely restricted in high water fractions due to molecular aggregation. This was further confirmed from colour Commission Internationale de l'Eclairage values as well as dynamic light scattering analysis. Third-order nonlinear optical properties were studied using a Nd:Yag laser beam Z-scan technique at 532 nm. The open aperture Z-scan revealed that PPT and PPF towards the peak point endured strong saturable absorption, whereas PPP indicated a strong reverse saturable absorption process. The AIE and AIBSE mechanisms from undergoing restricted twisting intramolecular motion in the aggregated luminogens provide great insight into new developments in AIEgen materials for these optoelectronic materials.

Two new polymorphs of cis-perinone: crystal structures, physical and electric properties.

The crystal structures of two polymorphs of cis-perinone (bisbenzimidazo[2,1-b:1',2'-j]benzo[lmn][3,8]phenanthroline-6,9-dione, Pigment Red 194) were solved from single crystals obtained solvothermally from 1,2-dichlorobenzene or n-butanol at 220°C. Both crystal structures (space group P21/c) derive from stacking of flat molecules arranged due to π-π interaction. The melting points of these two polymorphs are 471°C and 468°C and their respective optical bandgaps are 1.94 eV and 1.71 eV. One of the polymorphs demonstrates drift and hopping mechanisms of electric conductivity, whereas the other one is dominated by the drift conductivity. The direct current (DC) electric conductivity of the samples are 4.77 × 10-13 S m-1 and 6.84 × 10-10 S m-1 at room temperature. The significant difference in DC conductivities can be explained by the dependence of the mobility and concentration of charge carriers on the structure of the samples.

Irreversible magnetic properties of nanocarbon.

Magnetization M(T, B) of powder and glassy samples containing carbon nanoparticles, not intentionally doped and doped with Ag, Au and Co, is investigated at temperatures T between - 3-300 K in magnetic fields B up to 5T. According to atomic force microscopy data, a system of carbon particles has a broad size distribution, given by the average and the maximum radii of -60 nm and - 110 nm, respectively. In low fields of B << B(K), where B(K) - 1T is the mean anisotropy field, M(T) exhibits large irreversibility or deviation of zero-field cooled and field-cooled magnetizations, which is suppressed completely at B > B(K). The dependence of M(B) saturates above B - 2T at T - 150-300 K and contains a large paramagnetic-like response below - 50-150 K. Hysteresis is observed already at 300 K and is characterized by a power-law temperature decay of the coercive field, B(c)(T). This is described by the exponent n approximately 0.8 and by the low-temperature values of B(c) (0) increasing from -36-53 mT in the undoped sample and those doped with Ag and Au, up to 80 mT in the Co-doped material, yielding the blocking temperatures T(b) approximately 400-580 K. Analysis of the experimental magnetization data above suggests distribution of the magnetization close to the surface of the particles, yielding a thickness of the near-surface layer, h, filled with localized magnetic moments, micro1 - microB, to be close to the average distance, a, between the moments, h approximately a - 1 nm. This is consistent with the origin of magnetism in nanocarbon being presumably due to intrinsic near-surface defects.

Metal-metal bonding in ScTaN2. A new compound in the system ScN-TaN.

Gray microcrystalline powders of ScTaN(2) were prepared from solid-state reactions of delta-ScN with Ta(3)N(5) powders at T = 1770 K. According to thermal analyses the compound is stable against oxidation by O(2) up to temperatures of T = 800 K. In an Ar atmosphere ScTaN(2) decomposes above T = 1250 K and in a N(2) atmosphere above T = 2000 K under release of N(2) to form delta-ScN and beta-Ta(2)N. The crystal structure (space group P6(3)/mmc, No. 194, a = 305.34(3) pm, c = 1056.85(9) pm, Z = 2) was refined on the basis of X-ray and neutron powder diffraction data. It comprises alternating layers of ScN(6/3) octahedra and trigonal TaN(6/3) prisms, which are also observed in the binary nitrides delta-ScN and theta-TaN, respectively. A small degree of anti-site defects (about 5%) was detected. Only a small solubility of ScN in epsilon-TaN was observed, while the solubility of TaN in delta-ScN is >/=10 mol % at T = 1820 K. ScTaN(2) is a diamagnetic small gap semiconductor or a semimetal, as inferred from magnetization and electrical resistivity measurements, consistent with band structure calculations. Chemical bonding analyses with the COHP method yield significant covalent Ta-Ta interactions. Topological analyses of the electron localization function reveal unexpected Ta-Ta three-center bonding basins within seemingly empty trigonal prisms of the TaN(6/3) layers.

Polymorphism of heptalithium nitridovanadate(V) Li7[VN4].

The system Li-V-N was studied by means of X-ray and neutron powder diffraction, thermal and chemical analyses, and XAS spectroscopy at the vanadium K-edge. Three polymorphs of Li(7)[VN(4)] have been established from X-ray and neutron powder diffraction (gamma-Li(7)[VN(4)], space group Pfourmacr;3n, No. 218, a = 960.90(4) pm, V = 887.23(6) x 10(6) pm(3), Z = 8; beta-Li(7)[VN(4)], space group Pathremacr;, No. 205, a = 959.48(3) pm, V = 883.31(5) x 10(6) pm(3), Z = 8; alpha-Li(7)[VN(4)], P4(2)/nmc, No. 137, a = 675.90(2) pm, c = 488.34(2) pm, V = 223.09(1) x 10(6) pm(3), Z = 2). Crystallographic and phase relations are discussed. All three modifications are diamagnetic, indicating vanadium in the oxidation state +5. The V-K XAS spectra support the oxidation state assignment, the non-centrosymmetric coordination (tetrahedral), and the nearly identical second coordination sphere of vanadium, made up from Li in all three phases. The 3d-related features of the spectra display strongly localized properties. The phase transitions appear to be reconstructive; no direct group-subgroup symmetry relations of the crystal structures exist. The formation of solid solutions between Li(2)O and beta-Li(7)[VN(4)] with the general formula Li(1.75)((V(0.25(1)(-)(x))Li(0.25)(x))(N(1)(-)(x)O(x)())) with 0