Engineering Nanoarchitectures for Photonic Crystals

The detailed shape of the dense material network of inverse opals has a significant influence on the appearance of band gaps in these photonic crystals. One example of these topologically very similar networks is the skeleton structure, which can show two complete band gaps. Like all inverse opals, these structures are self‐standing and can be fabricated via self‐assembly strategies. The first step for obtaining these novel kind of photonic crystals has been achieved by synthesizing a titania skeleton structure.     

Strong Antiferromagnetic Coupling of Spins in the (MDABCO+)(C60.−) Salt with 3D Close Packing of the C60.− Radical Anions (MDABCO+: N‐Methyldiazabicyclooctanium Cation)

A new salt, (MDABCO⁺)(C₆₀^.?) ( 1 ; MDABCO⁺=N‐methyldiazabicyclooctanium cation), was obtained as single crystals. The crystal structure of 1 determined at 250 and 100 K showed 3D close packing of fullerenes with eight fullerene neighbors for each C₆₀^.?. These neighbors are located at 10.01–10.11 Å center‐to‐center distances (250 K) and van der Waals interfullerene C???C contacts are formed with four fullerene neighbors arranged in the bc plane. Fullerene ordering observed below 160 K is accompanied by the appearance of one and a half independent C₆₀^.? and trebling of the unit cell along the b axis. Fullerenes are packed closer to each other at 100 K. As a result, fullerenes are located in the three‐dimensional packing at 9.91–10.12 Å center‐to‐center distances and 18 short interfullerene C???C contacts are formed for each C₆₀^.?. Although they are closed packed, fullerenes are not dimerized down to 1.9 K. Magnetic data indicate strong antiferromagnetic coupling of spins in the 70–300 K range with a Weiss temperature of Θ=?118 K. Magnetic susceptibility shows a round maximum at 46 K. Such behavior can be described well by the Heisenberg model for square two‐dimensional antiferromagnetic coupling of spins with an exchange interaction of J/k_B=?25.3 K. This magnetic coupling is one of the strongest observed for C₆₀^.? salts.     

A Robust Microfluidic Device for the Synthesis and Crystal Growth of Organometallic Polymers with Highly Organized Structures

A simple and robust microfluidic device was developed to synthesize organometallic polymers with highly organized structures. The device is compatible with organic solvents. Reactants are loaded into pairs of reservoirs connected by a 15 cm long microchannel prefilled with solvents, thus allowing long‐term counter diffusion for self‐assembly of organometallic polymers. The process can be monitored, and the resulting crystalline polymers are harvested without damage. The device was used to synthesize three insoluble silver acetylides as single crystals of X‐ray diffraction quality. Importantly, for the first time, the single‐crystal structure of silver phenylacetylide was determined. The reported approach may have wide applications, such as crystallization of membrane proteins, synthesis and crystal growth of organic, inorganic, and polymeric coordination compounds, whose single crystals cannot be obtained using traditional methods.     

Spiral‐Type Heteropolyhedral Coordination Network Based on Single‐Crystal LiSrPO4: Implications for Luminescent Materials

Novel structures of luminescent materials, which are used as light sources for next‐generation illumination, are continuously being improved for use in white‐light‐emitting diodes. Activator‐doped known structures are reported as habitual down‐conversion phosphors in solid‐state lightings and displays. Consequently, the intrinsic qualities of the existent compounds produce deficiencies that limit their applications. Herein we report a spiral‐network single‐crystal orthophosphate (LiSrPO₄) prepared in a platinum crucible with LiCl flux through crystal‐growth reactions of SrCl₂ and Li₃PO₄ in air. It crystallizes in a hexagonal system with a=5.0040(2) and c=24.6320(16) Å, V=534.15(5) ų, and Z=6 in the space group P6₅. The unit cell is comprised of LiO₄ and PO₄ tetrahedrons that form a three‐dimensional LiPO₄^2? anionic framework with a helical channel structure along the c axis in which the Sr²⁺ cation is accommodated. The optical band gap of this composition is about 3.65 eV, as determined by using UV/Vis absorption and diffuse reflection spectra. We used the crystal‐growth method to synthesize blue‐ and red‐emitting crystals that exhibited pure color, low reabsorption, a large Stokes shift, and efficient conversion of ultraviolet excitation light into visible light. Emphasis was placed on the development of gratifying structure‐related properties of rare‐earth luminescent materials and their applications.     

Similar Structural Dynamics for the Degradation of CH3NH3PbI3 in Air and in Vacuum

We investigate the degradation path of MAPbI₃ (MA=methylammonium) films over flat TiO₂ substrates at room temperature by means of X‐ray diffraction, spectroscopic ellipsometry, X‐ray photoelectron spectroscopy, and high‐resolution transmission electron microscopy. The degradation dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodynamic mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic atomic arrangement. This early stage is followed by a phase change towards PbI₂. We describe how this degradation product is structurally coupled with the original MAPbI₃ lattice through the orientation of its constituent PbI₆ octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH₃NH₂ or MAI, with a relatively low energy cost. Our experiments also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material.     

Crystal-plane-dependent photoluminescence of pentacene 1D wire and 2D disk crystals

Down to the wire: Pentacene exhibits crystal-plane-dependent photoluminescence (PL) activity, as demonstrated in highly crystalline 1D?wires and 2D?disks, which were selectively synthesized using the vaporization-condensation-recrystallization (VCR) process. Although pentacene 1D?wires and 2D?disks have identical triclinic crystal structures, PL?activity is observed only from pentacene 1D?wires owing to the presence of "PL-active" (010) planes.     

Crystal Structures and Emitting Properties of Trifluoromethylaminoquinoline Derivatives: Thermal Single‐Crystal‐to‐Single‐Crystal Transformation of Polymorphic Crystals That Emit Different Colors

2,4‐Trifluoromethylquinoline (TFMAQ) derivatives that have amine ( 1 ), methylamine ( 2 ), phenylamine ( 3 ), and dimethylamine ( 4 ) substituents at the 7‐position of the quinoline ring were prepared and crystallized. Six crystals including the crystal polymorphs of 2 (crystal GB and YG) and 3 (crystal B and G) were obtained and characterized by X‐ray crystallography. In solution, TFMAQ derivatives emitted relatively strong fluorescence (${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =418–469 nm and Φ_f(s)=0.23–0.60) depending on the solvent polarity. From Lippert–Mataga plots, Δμ values in the range of 7.8–14 D were obtained. In the crystalline state, TFMAQ derivatives emitted at longer wavelengths (${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =464–530 nm) with lower intensity (Φ_f(c)=0.01–0.28) than those in n‐hexane solution. The polymorphous crystals of 2 and 3 emitted different colors: 2 , ${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =470 and 530 nm with Φ_f(c)=0.04 and approximately 0.01 for crystal GB and YG, respectively; and 3 , ${\lambda {{{\rm f}\hfill \atop {\rm max}\hfill}}}$ =464 and 506 nm with Φ_f(c)=0.28 and approximately 0.28 for crystal B and G, respectively. In both crystal polymorphs of 2 and 3 , crystals GB and G showed emission color changes by heating/melting/cooling cycles that were representative. By following the color changes in heating at the temperature below the melting point with X‐ray diffraction measurements and X‐ray crystallography, the single‐crystal‐to‐single‐crystal transformations from crystal GB to YG for 2 and from crystal B to G for 3 were revealed.     

Systematic Investigation of Molecular Arrangements and Solid‐State Fluorescence Properties on Salts of Anthracene‐2,6‐disulfonic Acid with Aliphatic Primary Amines

Organic salts of anthracene‐2,6‐disulfonic acid (ADS) with a wide variety of primary amines have been fabricated, and their arrangements of anthracene molecules and solid‐state fluorescence properties investigated. Single‐crystal X‐ray studies reveal that the salts show seven types of crystal forms and corresponding molecular arrangements of anthracene moieties depending on the amine, while anthracene shows only one form and arrangement in the solid state. Depending on the molecular arrangements, the ADS salts exhibit various solid‐state fluorescence properties: spectral shift (30 nm) and suppression and enhancement of the fluorescence intensity. Especially the ADS salt with n‐heptylamine (nHepA), which shows discrete anthracene moieties in the crystal, exhibits the highest quantum yield (Φ_F=46.1±0.2 %) in the series of ADS salts, which exceeds that of anthracene crystal (Φ_F=42.9±0.2 %). From these systematic investigations on the arrangements and the solid‐state properties, the following factors are essential for high fluorescence quantum yield in the solid state: prevention of contact between π planes of anthracene moieties and immobilization of anthracene rings. In addition, such organic salts have potential as a system for modulating the molecular arrangements of fluorophores and the concomitant solid‐state properties. Thus, systematic investigation of this system constructs a library of arrangements and properties, and the library leads to remarkable strategies for the development of organic solid materials.     

Iron Fluoride Hollow Porous Microspheres: Facile Solution‐Phase Synthesis and Their Application for Li‐Ion Battery Cathodes

Iron fluoride cathodes have been attracting considerable interest due to their high electromotive force value of 2.7 V and their high theoretical capacity of 237 mA h g^?1 (1 e^? transfer). In this study, uniform iron fluoride hollow porous microspheres have been synthesized for the first time by using a facile and scalable solution‐phase route. These uniform porous and hollow microspheres show a high specific capacity of 210 mA h g^?1 at 0.1 C, and excellent rate capability (100 mA h g^?1 at 1 C) between 1.7 and 4.5 V versus Li/Li⁺. When in the range of 1.3 to 4.5 V, stable capacity was achieved at 350 mA h g^?1 at a current of 50 mA g^?1.     

Structure,Optical, and Magnetic Properties of (PPN+)2(C702−)⋅2 C6H4Cl2, which Contains Dianionic Polymeric (C702−)n Chains

A new salt, (PPN⁺)₂(C₇₀^2?) ? 2 C₆H₄Cl₂ ( 1 ), which contains C₇₀^2? dianions, has been obtained as single crystals (PPN⁺=bis(triphenylphosphine)iminium cation). The C₇₀^2? dianions form polymeric zigzag (C₇₀^2?)_n chains, in which the fullerene units are bonded through single C? C bonds of length 1.581(5)–1.586(6) Å. The distance between the centers of neighboring C₇₀^2? units is 10.441 Å. The optical and magnetic properties of (C₇₀^2?)_n have also been studied. Decreasing the symmetry of C₇₀ in the polymer activate about 20 new IR bands in addition to the 10 IR‐active bands of the starting C₇₀. The polymeric structure shows absorptions in the visible and NIR regions, with three main bands at 890, 1200, and 1550 nm, instead of one band of isolated C₇₀^2? dianions at 1165–1184 nm. We concluded that the (C₇₀^2?)_n polymer was diamagnetic, with a negative molar magnetic susceptibility of ?3.82×10^?4 emu mol^?1 per C₇₀^2? dianion. The polymer is EPR silent and a weak narrow EPR signal in salt 1 is due to impurities, which only constitute 0.84 % of spin S=1/2 of the total amount of fullerene C₇₀.