β-Na(Y1.5Na0.5)F6:Tm—A blue upconversion phosphor

A luminescent material β-Na(Y_1.5Na_0.5)F₆ doped with Tm³⁺ was synthesized by a solid-state reaction method for a steady phosphor of blue upconversion. Under the 671 nm laser excitation, the green emission band of 511 nm due to the ¹D₂→³H₅ transition is obtained for the first time, while the ultraviolet emission band is also observed at 368 nm, associated with the ¹D₂→³H₆ transition. Especially, a wide band of blue emissions is obtained at the wavelength region of 440-490 nm, originated mainly from the ¹D₂→³F₄ (450 nm) and ¹G₄→³H₆ (471-487 nm) transitions, which have potential application in tunable solid-state blue laser of Tm³⁺. The upconversion mechanism is explored in terms of the energy-level structures of Tm³⁺ ion and the power dependence of upconverted emission intensity, which is believed to be performed by excited-state absorption.     

On the stability of the polaron in one dimensional disordered systems

A one-dimensional disordered system of electrons described by a tight binding model interacting with vibrational degrees of freedom (in harmonic approximation) is considered. A stable configuration is determined by a numerical minimization of the total energy which is based on the adiabatic approximation. The behaviour of the electron density (charge density wave) and the density of states is analysed. The localization properties are investigated as well. In contrast to the corresponding disordered system with vanishing electron-phonon coupling the present model has an energy gap. The formation of the gap and the polaron band is shown to be quite different for both onsite and intersite types of coupling terms. For large disorder, the lattice distortion and the gap disappear if only the vibrational contribution to the intersite coupling is important. They increase, however, if only the vibrational contribution to the site energies is taken into account. In both cases the localization length decreases upon increasing the electron-phonon coupling energy. The results are discussed with respect to low dimensional organic materials and amorphous semiconductors.     

Theoretical studies on the properties of uracil and its dimer upon thioketo substitution

The influences of thioketo substitution on the properties of uracil monomer and dimer and their interactions with Zn²⁺ have been systematically investigated at the B3LYP/6-311+G^*level of theory. Those properties include the structural characteristics, acidities, ionization potentials, and singlet–triplet energy gaps of SU monomers and their dimers, where SU=2-thiouracil, 4-thiouracil, and 2,4-dithiouracil, respectively. Computational results suggest that thioketo substitution leads to an increase in the acidities of the N-H groups for both uracil and its dimer, where the N₁–H group is still the most acidic site relative to that of N₃–H group. However, the opposite behaviors are true for the ionization potentials and the singlet–triplet energy gaps of uracil monomer and its dimer, suggesting that thiouracils are more susceptible to radiation damage relative to the unsubstituted uracil. For uracil and 2-thiouracil, the corresponding triplet excited-state geometries are predicted to be highly nonplanar compared with the planar geometries of the ground state as well as 4-thiouracil and 2,4-dithiouracil upon triplet excitation. As a rule, the intermolecular H-bonds involving the sulfur atom directly have been influenced more significant than those the oxygen atom directly involved for U::U and SU::SU base pairs upon ionization and excitation. Additionally, Zn²⁺ binding is expected to lead to an increase in the stability of U::U and SU::SU base pairs.     

Silver(I) complexes in coordination supramolecular system with bulky acridine-based ligands: syntheses, crystal structures, and theoretical investigations on C-H...Ag close interaction

In our efforts to investigate the coordination architectures of transition metals and organic ligands with tailored structures, we have prepared two structurally related rigid bulky acridine-based ligands, 9-[3-(2-pyridyl)pyrazol-1-yl]- acridine (L(1)) and 9-(1-imidazolyl)acridine (L2), and synthesized and characterized four of their Ag(I) complexes, {[AgL1](ClO4)}2 (1), {[AgL1](NO3)}2 (2), [AgL2(2)](ClO4) (3), and {[(Ag3L2(3))(NO3)](NO3)2(H2O)}(infinity) (4). The single-crystal X-ray diffraction analysis shows that the structures of 1 and 2 are similar to each other, with the two intramolecular Ag(I) centers of each complex being encircled by two L1 ligands; this forms a unique boxlike cyclic dimer, which is further linked to form one-dimensional (1D) chains of 1 and a two-dimensional (2D) network of 2 by intermolecular face-to-face pi...pi stacking and/or weak C-H...O hydrogen-bonding interactions, respectively. 3 has a mononuclear structure, which is further assembled into a 2D network via intermolecular Ag...O and pi...pi stacking weak interactions. 4 possesses two different 1D motifs that are further interlinked through interlayer face-to-face pi...pi stacking and Ag...O weak interactions, resulting in a 2D network. It is worth noting that one of the interesting structural features of 1, 2, and 4 is the presence of obvious C-H...M hydrogen-bonding interactions between the Ag centers and some acridine ring H atoms identified by X-ray diffraction on the basis of the van der Waals radii. Furthermore, as a representative example, full geometry optimization on the basis of the experimental structure, the natural bond orbital (NBO), and topological analysis of 1 were carried out by DFT and AIM (Atoms in Molecules) calculations. The total C-H...Ag interaction energy in 1 is estimated to be about 14 kJ/mol. Therefore, this work offers three new rare examples (1, 2, and 4) that exhibit C-H...Ag weak interactions, in which the N donors of the acridine rings coordinate to Ag(I) ions. Also, these results strongly support the existence of C-H...Ag close interactions and allow us to have a better understanding of the nature of such interactions in the coordination supramolecular systems.     

Ultrasound‐Assisted Construction of Halogen‐Bonded Nanosized Cocrystals That Exhibit Thermosensitive Luminescence

Multi‐component organic nanocrystals that are comprised of two or more supramolecular building blocks can be used to extend the design and assembly scope of solid molecular materials. Herein, we report the use of ultrasonication to prepare halogen‐bonded stilbene‐based nano‐cocrystals that exhibit different photoemission properties, including one‐ and two‐phonon emission and fluorescence lifetimes, relative to those of macrodimensional crystals. The structural transformation from nano‐cocrystals into nanocrystals upon heating results in a luminescence red‐shift from greenish blue to yellow. The temperature‐dependent ratiometric luminescence may allow such nano‐cocrystals to be used as fluorescent sensors and thermosensitive materials.     

Efficient One-Step Synthesis of N,N′-Bis(2-Hydroxy-5-Bromobenzylidene) Arylmethamediamines

The tittle compounds have directly been synthesized by one-step reaction of two different aldehydes in the presence of ammonia in good to excellent yields.     

Gold(I)-catalyzed intramolecular cyclopropanation of dienynes

Gold(I) complexes are the most active catalysts for the biscyclopropanation of dienynes to form tetracyclic compounds. PtII and ZnII are also able to promote the biscyclopropanation, although less efficiently. The configurations obtained in all cases with the use of gold(I) catalysts can be explained by the pathway proceeding through anti cyclopropyl gold carbenes. Similar intermediates are most probably involved in reactions catalyzed by RuII and PtII. Two different cyclopropanation pathways have been found; they depend on the structures of the cyclopropyl gold carbenes (anti or syn) and the relative arrangements of the metal carbenes and the alkenes.     

新的不对称双Schiff碱镍配合物

乙二胺中2个氨基具有相同的反应活性,易同时反应形成对称的双Schiff碱,随着不对称配合物的设计和金属酶模型化合物的不断开发,业已发现严格控制反应条件和改变反应物摩尔比,可以有效地实现单个氨基的选择性反应,例如,在低温、稀的反应液中,乙酰丙     

微量稀土对超导稳定化基体铜材的性能和组织的影响

研究了微量稀土元素对铜的机械性能、导电性和组织的影响，在铜中加入微量钇、钕、镝、铒和富铈混合稀土后，使铜的抗拉强度有所提高，并保持良好的塑性和导电性。