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Significant differences in the photochemical and photophysical behavior of

Cholesta-5,7,9(11)-trien-3β-ol (9,11-dehydroprovitamin D3, CTL) is used as a fluorescent probe to track the presence and migration of cholesterol in vivo. We recently described the photochemistry and photophysics of CTL in degassed and air-saturated tetrahydrofuran (THF) solution, an aprotic solvent. The zwitterionic nature of the singlet excited state, 1CTL* is revealed in ethanol, a protic solvent. In ethanol, the products observed in THF are accompanied by ether photoadducts and by photoreduction of the triene moiety to four dienes, including provitamin D3. The major diene retains the conjugated s-trans-diene chromophore and the minor is unconjugated, involving 1,4-addition of H at the 7 and 11 positions. In the presence of air, peroxide formation is a major reaction channel as in THF. X-ray crystallography confirmed the identification of two of the new diene products as well as of a peroxide rearrangement product.

Ionically bonded organic metal halide hybrids have emerged as versatile multicomponent material systems exhibiting unique and useful properties. The unlimited combinations of organic cations and metal halides lead to the tremendous structural diversity of this class of materials, which could unlock many undiscovered properties of both organic cations and metal halides. Here we report the synthesis and characterization of a series benzoquinolinium (BZQ) metal halides with a general formula (BZQ)Pb2X5 (X = Cl, Br), in which metal halides form a unique two-dimensional (2D) structure. These BZQ metal halides are found to exhibit enhanced photoluminescence and stability as compared to the pristine BZQ halides, due to the scaffolding effects of 2D metal halides. Optical characterizations and theoretical calculations reveal that BZQ+ cations are responsible for the emissions in these hybrid materials. Changing the halide from Cl to Br introduces heavy atom effects, resulting in yellow room temperature phosphorescence (RTP) from BZQ+ cations.

Binuclear platinum(II) complexes with strong Pt-Pt interactions are an interesting class of luminescent materials, of which photophysical properties could be controlled via multiple ways through organic ligands and Pt-Pt distance. While a number of binuclear platinum(II) complexes have been developed with tunable emissions, achieving high photoluminescence quantum efficiency (PLQE) remains challenging and of great interest. Here we report the synthesis and characterization of a series of binuclear 2,4-difluorophenylpyridine platinum(II) complexes bridged by thiazol-2-thiolate ligands with different bulkiness. The three complexes were found to have short Pt-Pt distances ranging from 2.916 to 2.945 Å. The strong Pt-Pt interactions lead to pronounced metal-metal-to-ligand charge transfer (MMLCT) absorptions between 450 and 500 nm, and strong

The two metal-deficient series of quaternary Ge-containing sulfides RE3M0.5GeS7 (RE = La–Nd, Sm; M = Co, Ni), as well as the related Si-containing sulfide Y3Pd0.5SiS7, were prepared by reactions of the elements at 1050 °C. Single-crystal X-ray diffraction analysis performed on all compounds confirmed noncentrosymmetric hexagonal structures (space group P63, Z =2) with cell parameters in the ranges of a =10.0–10.3 A and c =5.7–5.8 A for RE3Co0.5GeS7 and RE3Ni0.5GeS7, or a =9.7891(3) A and c =5.6840(4) A for Y3Pd0.5SiS7. They are classified as La3Mn0.5SiS7-type structures, with M atoms centred within octahedra (in contrast to La3CuSiS7-type structures in which M atoms occupy trigonal planar sites) and Ge atoms centred within tetrahedra, both types of polyhedra being arranged in one-dimensional stacks aligned along the c-direction. Charge balance requirements dictate half-occupancy of the M sites. However, bond valence sum arguments indicated that the M atoms are somewhat underbonded within these octahedral sites, so that there is evidence that in some compounds, they can also enter the trigonal planar site at low occupancy (~5%). Magnetic measurements on RE3Co0.5GeS7 (RE = Ce, Pr, Sm) revealed paramagnetic behaviour for the Ce and Pr members and apparent antiferromagnetic ordering (TN =14 K) for the Sm member; fitting to the Curie-Weiss law gave effective magnetic moments consistent with the presence of RE3+ and Co2+ species. Band structure calculations on ordered models of La3M0.5GeS7 (M = Co, Ni) showed that the Fermi level cuts through M 3d states in the DOS curve and supported the presence of strong M–S and Ge–S bonding interactions.

A metal-organic cage (termed FJI-C9) based on six square-shaped Cu 2 (CO 2 ) 4 paddle-wheel building units and eight flexible 1,3,5-trimethyl-2,4,6-tris(3-phenoxymethyl)benzoic acid (TTBA) linkers has been constructed. The porous FJI-C9 containing large cage of 1.5 nm shows high CO 2 adsorption uptake.

The rich chemistry of metal halide perovskites has enabled various methods of band structure control and surface passivation. Here we report a highly facile and efficient post-treatment approach for precise color tuning of cesium lead halide perovskite nanocrystals (NCs) with enhanced stability. By utilizing a special multifunctional organic ligand, triphenyl(9-phenyl-9H-carbazol-3-yl)phosphonium bromide (TPP-Carz), carbon-halide bond cleavage can be achieved to release halide ions from halogenated solvents in a controlled manner for color tuning of perovskite NCs via ion exchange. Besides controlled release of halide ions for anion exchange, TPP-Carz can effectively passivate the surfaces of perovskite NCs simultaneously. As a result, perovskite NCs prepared by this post-treatment method with tunable colors over the entire visible spectrum have shown significantly improved luminescence and stability in comparison to the ones prepared using reactive anion precursors without surface passivation by TPP-Carz.

The selenide Ba4Ga4GeSe12, synthesized by reaction of BaSe, Ga2Se3, and GeSe2 at 1173 K, adopts a noncentrosymmetric tetragonal structure (space group P 4 ¯ 2 1 c , Z=2, a=13.5468(4) A, c=6.4915(2) A) consisting of a three-dimensional network built from two types of corner-sharing MSe4 tetrahedra, with Ba cations occupying the intervening voids. It is isostructural to Pb4Ga4GeS12, Pb4Ga4GeSe12, and Ba4Ga4SnSe12, but differs subtly in site ordering. Structural refinements and bond valence sum analysis suggest partial disorder manifested by mixing of 0.75 Ga and 0.25 Ge within one tetrahedral site, and occupation of exclusively Ga within the other tetrahedral site. The optical band gap of 2.18(2) eV, measured from the UV/VIS/NIR diffuse reflectance spectrum, agrees with a calculated gap of 2.35 eV between valence and conduction bands and is consistent with the orange-yellow color of the crystals. Nonlinear optical measurements on powder samples revealed a weak second harmonic generation signal using 2.09 µm as the fundamental laser wavelength.

The ternary selenide Ba4Ga2Se8 has been synthesized by reaction of BaSe, Ga2Se3, and Se at 1023 K. Single-crystal X-ray diffraction analysis revealed a monoclinic structure (space group P21/c, Z=4, a=13.2393(5) A, b=6.4305(2) A, c=20.6432(8) A, β=104.3148(6)°) featuring one-dimensional chains of corner-sharing Ga-centered tetrahedra and discrete S e 2 2 − anionic units, with charge-compensating Ba2+ cations located between them. The UV/vis/NIR diffuse reflectance spectrum reveals an optical band gap of 1.63(2) eV, which is consistent with the black color of the crystals and agrees with a calculated gap of 1.51 eV obtained from band structure calculations. The presence of the S e 2 2 − units narrows the band gap in Ba4Ga2Se8 relative to other Ba–Ga–Se phases.

The quaternary rare-earth chalcogenides RE 3 CuGaS 7 and RE 3 CuGaSe 7 ( RE =La–Nd) have been prepared by reactions of the elements at 1050 °C and 900 °C, respectively. They crystallize in the noncentrosymmetric La 3 CuSiS 7 -type structure (hexagonal, space group P 6 3 , Z =2) in which the a -parameter is largely controlled by the RE component ( a =10.0–10.3 A for the sulfides and 10.3–10.6 A for the selenides) whereas the c -parameter is essentially fixed by the choice of Ga and chalcogen atoms within tetrahedral units ( c =6.1 A for the sulfides and 6.4 A for the selenides). They extend the series RE 3 M Ga Ch 7 , previously known for divalent metal atoms ( M =Mn–Ni), differing in that the Cu atoms in RE 3 CuGa Ch 7 occupy trigonal planar sites instead of octahedral sites. Among quaternary chalcogenides RE 3 MM ′ Ch 7 , the combination of monovalent ( M =Cu) and trivalent ( M ′=Ga) metals is unusual because it appears to violate the condition of charge balance satisfied by most La 3 CuSiS 7 -type compounds. The possibility of divalent Cu atoms was ruled out by bond valence sum analysis, magnetic measurements, and X-ray photoelectron spectroscopy. The electron deficiency in RE 3 CuGa Ch 7 is accommodated through S-based holes at the top of the valence band, as shown by band structure calculations on La 3 CuGaS 7 . An optical band gap of about 2.0 eV was found for La 3 CuGaSe 7 .

The nonlinear optical (NLO) BaGa 4 S 7 polycrystalline materials with stoichiometric composition were synthesized from BaS, Ga, and S via solid-state reactions in the dual temperature zone rocking furnace with excess sulfur, and crystal BaGa 4 S 7 for the mid-infrared (IR) was grown with Bridgman–Stockbarger technique. The ultraviolet (UV) and IR optical absorption edges of crystal BaGa 4 S 7 were found to be at 350 nm and 13.7 μm, respectively. Its thermal conductivities at 50 °C were 1.45 W/(m K), 1.58 W/(m K) and 1.68 W/(m K) along a -, b - and c -directions, respectively. The laser damage threshold of a single crystal was about 7.1 J/cm 2 at 2.1 μm, and 26.2 J/cm 2 at 9.58 μm. The idler non-critical phase-matching OPO wavelength was between 6 and 10 μm when the pumped wavelength was varied around 2.2 μm.

Two series of Mn-substituted rare-earth zinc arsenides RE(1-y)Mn(x)Zn(2-x)As2 (RE = Eu-Lu) and RE(2-y)Mn(x)Zn(4-x)As4 (RE = La-Nd, Sm, Gd) were prepared by reaction of the elements at 750 °C. Both series are derived from ideal empirical formula REM2As2 (M = Mn, Zn) and adopt crystal structures related to the trigonal CaAl2Si2-type (space group P3m1) in which hexagonal nets of RE atoms and [M2As2] slabs built up of edge-sharing M-centered tetrahedra are alternately stacked along the c-direction. For compounds with divalent RE components (Eu, Yb), the fully stoichiometric and charge-balanced formula REM2As2 is obtained, with Mn and Zn atoms statistically disordered within the same tetrahedral site. For compounds with trivalent RE components, the RE sites become deficient, and the Mn atoms are segregated from the Zn atoms in separate tetrahedral sites. Within the series RE(1-y)Mn(x)Zn(2-x)As2 (Gd-Tm, Lu), the parent CaAl2Si2-type structure is retained, and the Mn atoms are disordered within partially occupied interstitial sites above and below [Zn(2-x)As2] slabs. Within the series RE(2-y)Mn(x)Zn(4-x)As4 (RE = La-Nd, Sm, Gd), the c-axis becomes doubled as a result of partial ordering of Mn atoms between every other pair of [Zn(2-x)As2] slabs. Attempts to synthesize Gd-containing solid solutions with the charge-balanced formula Gd0.67Mn(x)Zn(2-x)As2 suggested that these phases could be formed with up to 50% Mn substitution. Band structure calculations reveal that a hypothetical superstructure model with the formula La1.33MnZn3As4 would have no gap at the Fermi level and that slightly lowering the electron count alleviates antibonding Mn-As interactions; a spin-polarized calculation predicts nearly ferromagnetic half-metallic behavior. X-ray photoelectron spectroscopy confirms the presence of divalent Mn in these compounds.

Four series of ternary rare-earth zinc arsenides have been prepared by reaction of the elements at 750 °C: RE4Zn(2-x)As5 forming for RE = La-Nd, Sm; and RE5Zn(2-x)As6, RE6Zn(2-x)As7, RE7Zn(2-x)As8 forming for RE = Ce, Pr, Nd, Sm. They crystallize in trigonal structure types in space group P3m1 with Z = 1 for RE4Zn(2-x)As5 and RE7Zn(2-x)As8, or space group R3m1 with Z = 3 for RE5Zn(2-x)As6 and RE6Zn(2-x)As7. Through the structural principle of intergrowing rocksalt-type [REAs] slabs of variable thickness within a parent CaAl2Si2-type structure containing Zn-deficient [Zn(2-x)As2] slabs built from edge-sharing Zn-centered tetrahedra, these ternary arsenides belong to a homologous series with the formulation REZn(2-x)As2·n(REAs) (n = 3, 4, 5, 6). Quaternary derivatives Ce4(Mn,Zn)(2-x)As5 and Ce6(Mn,Zn)(2-x)As7 were also obtained in which Mn partially substitutes for Zn. Band structure calculations predict that the electronic properties can be gradually modified from semiconducting to semimetallic behavior as more [REAs] slabs are introduced.

The ternary rare-earth zinc arsenides RE Zn 2 As 3 ( RE =La–Pr) have been prepared by reactions of the elements at 800 °C. They adopt new tetragonal structure types, with the La member (space group I 4/ mmm , Z =4, a =4.1133(2) A, c =32.1246(14) A) differing from the Ce and Pr members (space group P 4/ nmm , Z =2, a =4.0804(6)–4.0534(12) A, c =16.089(5)–16.059(10) A, respectively) in the disposition of RE -centred square antiprisms on opposite sides of square As nets. The structures contain thick anionic slabs, built from edge-sharing ZnAs 4 tetrahedra, that can be considered either as stackings of three PbO-type layers or as fragments of the fluorite-type structure. These slabs are deficient in Zn and are reminiscent of the same features in binary arsenide Zn 3 As 2 . LaZn 2 As 3 exhibits temperature-independent paramagnetism whereas CeZn 2 As 3 follows modified Curie–Weiss behavior consistent with Ce 3+ species but with no occurrence of long-range ordering.

New middle infrared nonlinear optical crystals of BaGa{sub 2}GeX{sub 6}(X=S, Se) have been synthesized. The structures of both BaGa{sub 2}GeS{sub 6} and BaGa{sub 2}GeSe{sub 6} were found to be isomorphous exhibiting a three-dimensional framework constructed by the parallel alignment of Ga or Ge tetrahedron groups along the c-aix. The ultraviolet transmittance spectrum indicates the short-wavelength absorption edges of BaGa{sub 2}GeS{sub 6} and BaGa{sub 2}GeSe{sub 6} are 380 nm and 440 nm, respectively. The IR transmittance spectrum shows that the absorption edge of the BaGa{sub 2}GeS{sub 6} crystal is 13.7 {mu}m. Second-harmonic generation of the powder samples was measured with a 2.05 {mu}m laser using the Kurtz and Perry technique, which showed that BaGa{sub 2}GeS{sub 6} and BaGa{sub 2}GeSe{sub 6} are phase-matched materials, and their measured SHG coefficient is {approx}2.1 and {approx}3.5 times as large as the coefficient of AgGaS{sub 2}, or 26.3 pm/V and 43.7 pm/V. - Graphical abstract: The structure of BGGS viewed along the a and c axis and an as-grown crystal. Highlights: Black-Right-Pointing-Pointer Mid-IR NLO crystals of BaGa{sub 2}GeX{sub 6}(X=S, Se) with wide band-gap have been discovered. Black-Right-Pointing-Pointer The structures were constructed by the parallel alignment of Ga or Ge tetrahedra. Black-Right-Pointing-Pointer They are phase-matchable material withmore » their SHG coefficient of 26.3 and 43.7 pm/V.« less

Two new pillared-layer frameworks have been obtained through self-assembly of 4,4′-azobenzene dicarboxylatic acid (4,4′-H2ABDC), oxalate, hydroxyl and LnCl3(Ln = Sm, Eu) under hydrothermal environment and characterized by TGA, IR spectroscopy, element analyses, and X-ray single crystal diffraction. The X-ray structure analyses reveal that the oxalates link the Ln(III) to form metal layers, and 4,4′-ABDC ligands work as pillars to connect adjacent layers to further extend into 3D frameworks. Their magnetic studies show that the two compounds have typical anti-ferromagnetic behaviors.

A study was made on effect of niobium on the GdVO4 crystal structure. Yb:GdV0.995Nb0.005O4 crystals were grown by the Czochralski method, and their transmission spectra, absorption spectra, and fluorescence spectra were measured. The GdV0.995Nb0.005O4 crystals acting as new laser host crystals do not affect the absorption of Yb3+. Some spectrum parameters calculated by the Fuchbauer—Ladenburger method indicate that doping of Nb5+ in the GdVO4 crystal improves the spectroscopic properties of Yb3+.