Growth and spectral properties of Yb:Ca0.28Ba0.72Nb2O6 disordered crystal

The growth, XRD patterns, spectral properties, and fluorescence decays of Yb:Ca_0.28Ba_0.72Nb₂O₆ (Yb:CBN) with doping concentration of 1 at.% and 5 at.% were studied. The peak absorption cross-section and the emission cross-section were calculated. Larger Stark splitting of Yb:CBN offers the prospect of the quasi-four level laser operation.     

Application of the transmission line matrix method for outdoor sound propagation modelling – Part 1: Model presentation and evaluation

The present paper deals with an original time-domain approach applied to outdoor sound propagation under meteorological effects. The transmission line matrix method, based on the Huygens’ principle, had already been validated over impedant grounds and complex topography. The presented formulation proposes to take into account meteorological effects (wind speed and temperature) through the relative sound speed. The necessary wavefront direction is determined through the calculation of the averaged intensity vector direction. A good agreement is found between simulations of both the transmission line matrix and parabolic equation methods. A relevant use of the method is shown in the framework of environmental acoustics and initial applications are proposed in Part 2.     

(C5H6N)4[Be6(HPO3)8]·H2O: A low-density open-framework beryllium phosphite with multidirectional 12-ring channels

Employing the common pyridine (=py) solvent as the source of structure-directing agents (SDAs), a novel three-dimensional open-framework beryllium phosphite (Hpy)₄[Be₆(HPO₃)₈]·H₂O (1), has been solvothermally synthesized and structurally characterized by IR, elemental analysis, thermogravimetric analysis, powder and single-crystal X-ray diffractions. It crystallizes in the orthorhombic system, space group Pbca (No. 61), a = 20.0034(4) Å, b = 20.2188(4) Å, c = 20.9731(3) Å, V = 8482.5(3) Å³, and Z = 8. The alternating connection of BeO₄ tetrahedra and HPO₃ pseudopyramids give rise to a (3, 4)-connected network with multidirectional intersecting 12-ring channels. The compound possesses a low density and a new {4.8.10}{4².6.8.10.12}{4².6}₃{4².8.10².12}{4³.6².8} topology.     

Syntheses,characterization and nonlinear optical properties of sodium–scandium carbonate Na5Sc(CO3)4·2H2O

A novel nonlinear optical (NLO) material Na₅Sc(CO₃)₄·2H₂O has been synthesized under a subcritical hydrothermal condition. The structure is determined by single-crystal X-ray diffraction and further characterized by TG analyses and UV–vis–NIR diffuse reflectance spectrum. It crystallizes in the tetragonal space group P-421c, with a = b = 7.4622(6) Å, C = 11.5928(15) Å. The Second-harmonic generation (SHG) on polycrystalline samples was measured using the Kurtz and Perry technique, which indicated that Na₅Sc(CO₃)₄·2H₂O was a phase-matchable material, and its measured SHG coefficient was about 1.8 times as large as that of d₃₆ (KDP). The results from the UV–vis diffuse reflectance spectroscopy study of the powder samples indicated that the short-wavelength absorption edges of Na₅Sc(CO₃)₄·2H₂O is about 220 nm, suggesting that this crystal is a promising UV nonlinear optical (NLO) materials.     

Photophysical Properties and Efficient,Stable, Electrogenerated Chemiluminescence of Donor–Acceptor Molecules Exhibiting Thermal Spin Upconversion

The photophysical properties and electrogenerated chemiluminescence (ECL) of three donor–acceptor molecules composed of dicyanobenzene and methyl‐, tert‐butyl‐, and phenyl‐substituted carbazolyl groups, 1,2,3,5‐tetrakis(3,6‐disubstituted‐carbazol‐9‐yl)‐4,6‐dicyanobenzene (4CzIPN‐Me, 4CzIPN‐tBu, and 4CzIPN‐Ph, respectively) are described. These molecules show delayed fluorescence as a result of thermal spin upconversion from the lowest triplet state to the lowest singlet state at room temperature. The three molecules showed yellow to yellowish–red ECL. Remarkably, the ECL efficiencies of 4CzIPN‐tBu in dichloromethane reached almost 40 %. Moreover, stable ECL was emitted from 4CzIPN‐tBu and 4CzIPN‐Ph. In case of 4CzIPN‐Me, the ECL intensity decreased during voltage cycles because of polymerization. Quantum chemical calculations revealed that polymerization was inhibited by the steric hindrance of the bulky tert‐butyl and phenyl groups on the carbazolyl moieties and lowered the spin density on the carbazolyl groups through electron conjugation for 4CzIPN‐Ph.     

Simultaneous Aromatic–Beryllium Bonds and Aromatic–Anion Interactions: Naphthalene and Pyrene as Models of Fullerenes,Carbon Single‐Walled Nanotubes,and Graphene

The possibility of forming stable BeR₂:ArH:Y^? (R=H, F, Cl; ArH=naphthalene, pyrene; Y=Cl, Br) ternary complexes in which the beryllium compounds and anions are located on the opposite sides of an extended aromatic system is explored by means of MP2/aug‐cc‐pVDZ ab initio calculations. Comparison of the electron‐density distribution of these ternary complexes with the corresponding BeR₂:ArH and ArH:Y^? binary complexes reveals the existence of significant cooperativity between the two noncovalent interactions in the triads. The energetic effects of this cooperativity are quantified by evaluation of the three‐body interaction energy Δ³E in the framework of the many‐body interaction‐energy (MBIE) approach. Although an essential component of the interaction energies is electrostatic and is well reflected in the changes in the molecular electrostatic potential of the aromatic system on complexation, strong polarization effects, in particular for the BeR₂:ArH interactions, also play a significant role. The charge transfers associated with these polarization effects are responsible for significant distortion of both the BeR₂ and the aromatic moieties. The former are systematically bent in all the complexes, and the latter are curved to a degree that depends on the nature of the R substituents of the BeR₂ subunit.     

Computational Study of Proton Transfer in Tautomers of 3‐ and 5‐Hydroxypyrazole Assisted by Water

The tautomerism of 3‐ and 5‐hydroxypyrazole is studied at the B3LYP, CCSD and G3B3 computational levels, including the gas phase, PCM–water effects, and proton transfer assisted by water molecules. To understand the propensity of tautomerization, hydrogen‐bond acidity and basicity of neutral species is approached by means of correlations between donor/acceptor ability and H‐bond interaction energies. Tautomerism processes are highly dependent on the solvent environment, and a significant reduction of the transition barriers upon solvation is seen. In addition, the inclusion of a single water molecule to assist proton transfer decreases the barriers between tautomers. Although the second water molecule further reduces those barriers, its effect is less appreciable than the first one. Neutral species present more stable minima than anionic and cationic species, but relatively similar transition barriers to anionic tautomers.     

Regulating Molecular Recognition with C‐Shaped Strips Attained by Chirality‐Assisted Synthesis

Chirality‐assisted synthesis (CAS) is a general approach to control the shapes of large molecular strips. CAS is based on enantiomerically pure building blocks that are designed to strictly couple in a single geometric orientation. Fully shape‐persistent structures can thus be created, even in the form of linear chains. With CAS, selective recognition between large host and guest molecules can reliably be designed de novo. To demonstrate this concept, three C‐shaped strips that can embrace a pillar[5]arene macrocycle were synthesized. The pillar[5]arene bound to the strips was a better host for electron‐deficient guests than the free macrocycle. Experimental and computational evidence is provided for these unique cooperative interactions to illustrate how CAS could open the door towards the precise positioning of functional groups for regulated supramolecular recognition and catalysis.