Hoseop Yun

GUEST-INDUCED REORGANIZATION OF A SELF-ASSEMBLED PD(II) COMPLEX

Abstract A self-assembled two-dimensional Pd(II) complex derived from a bidentate ligand trans -1,2-bis(4-pyridyl)ethylene and (en)Pd(NO 3 ) 2 in D 2 O showed concentration dependent and guest-induced reorganization behavior. While the trimeric assembly is induced either at very low concentration or in the presence of guest complementary to the trimer cavity, the tetrameric assembly is induced either in less dilute solution or in the presence of guest with better van der Waals contacts with the tetramer cavity surface. Especially, in the case of using 1,3-adamantanedicar☐ylic acid disodium salts as a guest, all the oligomeric forms disappeared and only a single, tetrameric assembly was clearly induced.

High-power Broadband Organic THz Generator

The high-power broadband terahertz (THz) generator is an essential tool for a wide range of THz applications. Here, we present a novel highly efficient electro-optic quinolinium single crystal for THz wave generation. For obtaining intense and broadband THz waves by optical-to-THz frequency conversion, a quinolinium crystal was developed to fulfill all the requirements, which are in general extremely difficult to maintain simultaneously in a single medium, such as a large macroscopic electro-optic response and excellent crystal characteristics including a large crystal size with desired facets, good environmental stability, high optical quality, wide transparency range, and controllable crystal thickness. Compared to the benchmark inorganic and organic crystals, the new quinolinium crystal possesses excellent crystal properties and THz generation characteristics with broader THz spectral coverage and higher THz conversion efficiency at the technologically important pump wavelength of 800 nm. Therefore, the quinolinium crystal offers great potential for efficient and gap-free broadband THz wave generation.

Acentric nonlinear optical N-benzyl stilbazolium crystals with high environmental stability and enhanced molecular nonlinearity in solid state

We have developed a new cation core structure, N-benzyl stilbazolium nonlinear optical chromophore with a non-polar benzyl group to achieve acentric molecular ordering in the crystalline state. New N-benzyl stilbazolium crystal, BP3 (N,N-dimethylamino-N′-2,5-dimethylbenzyl-stilbazolium p-toluenesulfonate), exhibits an acentric crystal structure with the monoclinic P21 phase with a large macroscopic optical nonlinearity of 540 times the powder second harmonic generation efficiency of urea at the non-resonant wavelength of 1.9 µm. Compared to conventional rod-shaped N-alkyl stilbazolium crystals, an enhanced hyperpolarizability of the chromophoresβ0 in the solid state can be utilized in bent-shaped N-benzyl stilbazolium crystals. This is attributed to the decreased inter-chromophore interactions due to the larger chromophore–chromophore separation induced by the bulky and bent-shaped N-benzyl group, so-called site-isolation effect. Moreover, by introducing the non-polar dimethylbenzyl group, BP3 crystals show a high environmental stability: they exhibit almost one order of magnitude smaller solubility in water than conventional stilbazolium crystals and also do not form a hydrated centrosymmetric phase even if crystallized in water-containing solvents. We have grown good optical quality crystals large enough for optical characterization. With as-grown BP3 crystals without additional polishing and cutting procedures we have demonstrated THz generation by optical rectification using 180 fs pulses at the pump wavelength of 836 nm.

New synthesis and ring opening of cis-3-alkylaziridine-2-carboxylates

Abstract Syntheses of cis-3-alkylaziridine-2-carboxylates including cis-3-benzyl- and cis-3-phenylaziridine-2-carboxylates were achieved from the reaction of α-aminonitrile and alkyldiazoacetate in the presence of a Lewis acid. Asymmetric version of this reaction with the chiral α-methylbenzylamine was also successful for the preparation of chiral aziridines that were used for the synthesis of various amino acids including homophenylalanine, β-amino-α-hydroxy acid, α,β-diamino acid, and α-amino-β-hydroxy acid via regioselective aziridine ring openings.

Influence of phenolic hydroxyl groups on second-order optical nonlinearity at an example of 2,4- and 3,4-dihydroxyl hydrazone isomorphic crystals

We investigate the crystal structure and physical properties of 2,4- and 3,4-dihydroxybenzaldehyde-4-nitrophenylhydrazone (DHNPH) isomer crystals to understand the relation between molecular ordering with noncovalent interactions based on phenolic OH groups. The microscopic and macroscopic optical nonlinearities of 2,4- and 3,4-DHNPH crystals are investigated experimentally and theoretically by using density functional theory calculations. Although the two isomer crystals possess a very similar molecular orientation based on a similar supramolecular synthon, 2,4-DHNPH exhibits a 1.7 times larger powder second harmonic generation efficiency than 3,4-DHNPH, which is attributed to their different intermolecular interactions involving phenolic OH groups. We show that the microscopic nonlinearity of the DHNPH molecules is particularly sensitive to variations in phenolic OH characteristics such as the orientation and intermolecular interactions.

Crystal structure and magnetic properties of dicarboxylate-bridged linear chain Mn(II) complexes

Abstract Two manganese(II) complexes, [Mn(mtm)(CH3OH)2(H2O)]n (1) and [Mn2(mtm)2(2,2′-bipy)2]n (2) (bipy=bipyridine, mtm=[bis(methylthio)methylene]malonate) were synthesized and characterized by X-ray crystallography. Structure of 1 consists of octahedral manganese(II) species which are extended by carboxylate bridges in syn–anti fashion along the c-axis. Chains of 1 are associated by hydrogen bonding among coordinating water and methanol molecules and carboxylate oxygen atoms, forming two-dimensional structures. The crystallographic asymmetric unit of 2 comprises two [Mn(2,2′-bipy)(mtm)] units in which Mn(II) atoms are bridged by μ2-oxygens from carboxylate to form Mn2O2 rhombus. The dimeric units are linked doubly by second carboxylates in syn–anti fashion, resulting in a chain structure. The antiferromagnetic coupling of Mn(II) ions in 1 (−0.2 cm−1) and 2 (−1.57 cm−1) was determined from variable-temperature magnetic susceptibility data in the temperature range of 2–300 K.

Crystal engineering by eliminating weak hydrogen bonding sites in phenolic polyene nonlinear optical crystals

A new acentric polyene crystal OH3 with a large macroscopic second-order optical nonlinearity with optimal chromophore orientation for electro-optics and THz-wave applications has been developed by crystal engineering, eliminating weak CH⋯NC hydrogen-bonding sites, but still retaining strong OH⋯NC hydrogen-bonding sites of the analogue OH1 crystals.

A new quaternary thiophosphate, RbNb2(S2)3(PS4)

The structure of the new quaternary thiophosphate rubidium diniobium tris(disulfide) tetrathiophosphate, RbNb(2)(S2)(3)(PS4), is made up of one-dimensional (infinity)(1)[Nb(2)(S2)(3)(PS4)(-)] chains along the [101] direction, and these chains are separated from one another by Rb(+) ions. The chain is basically built up from [Nb(2)S(12)] units and tetrahedral [PS(4)] groups. The [Nb(2)S(12)] units are linked together to form a linear [Nb(2)S(9)] chain by sharing the S-S prism edge. Short and long Nb-Nb distances [2.888 (2) and 3.760 (2) A, respectively] alternate along the chain, and the anionic species S(2)(2-) and S(2-) are observed.

Rodlike mesogenic molecules consisting of two diacetylenic groups: mesomorphic behavior and photoimaging

A series of mesogenic compounds with two diacetylenic groups were synthesized. The diacetylene groups were connected to a benzene ring via ester linkages, becoming a part of a rigid rod. The thermal behavior of the compounds and their polymerization were investigated. Compounds 7, 8, 9 and 10 having long alkyl tails showed nematic mesophases. They were thermally polymerized in the isotropic state above 200 °C. Partial polymerization occurred by annealing in the liquid crystalline state. When the compounds were exposed to UV light in the liquid crystalline state, the polymerization was completed within 30 min to give amorphous polydiacetylenes. In the UV-Vis spectra, absorption of the polymers occurred up to about 600 nm, attributable to the short conjugated polydiacetylene backbones. Compound 9 with an octyl tail was fabricated into a thin film and the photopolymerization was carried out through a photomask in the liquid crystalline state resulting in a patterned image.

Di­cyano{[(1S)-(1-phenyl­ethyl)­aziridin-2-yl]­methano­lato-κ2N,O}boron

In the title compound, C 13 H 14 BN 3 O, the aziridine ring is an almost equilateral triangle, the C-C distance being slightly shorter than the C-N distances, probably because of the dative B-N bond. The five-membered ring, composed of two C atoms and N, B and O atoms, is fused with the aziridine ring to form a six-membered ring with a chair conformation.