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Zürich, Switzerland

Kim J.,Korea Advanced Institute of Science and Technology | Kwon O.-P.,Ajou University | Jazbinsek M.,Rainbow Photonics AG | Park Y.C.,Korea Advanced Institute of Science and Technology | And 2 more authors.
Journal of Physical Chemistry C | Year: 2011

The direction and the magnitude of the first hyperpolarizability are investigated by the finite field (FF) method for organic nonlinear optical ionic chromophores and crystals with an isotropic counteranion, either a point charge or hexafluorophosphate. Simple model compound 4-aminopyridinium and DAPSH (N,N-dimethylamino-N′-phenyl-4-stilbazolium hexafluorophosphate) crystal with the highest quadratic optical nonlinearities measured to date in organic crystals, as well as stilbazolium derivatives having heteroaromatic and/or bulky aromatic rings, are investigated. Calculations indicate that the extrinsic isotropic point-charges or anions almost have no effect on the direction of the intrinsic first hyperpolarizability of the cation chromophores, and induce a limited increase of the magnitude smaller than ∼15% due to their asymmetric distribution with respect to the pyridinium nitrogen atom. This finding enables one to simply approximate the first hyperpolarizability of ionic crystalline systems having 1D intramolecular charge transfer character by considering only the cation. In addition, the heteroaromatic or bulky aromatic substituents at the end of the pyridinium acceptor intrinsically do not affect the direction and only moderately affect the magnitude of the first hyperpolarizability of stilbazolium salts. These results are potentially useful for molecular design and crystal engineering of ionic organic materials, where the magnitude and the direction of first hyperpolarizability as well as the shape of the ionic chromophore are of great importance. © 2011 American Chemical Society. Source

Kim P.-J.,Ajou University | Jazbinsek M.,Rainbow Photonics AG | Kwon O.-P.,Ajou University
Crystal Growth and Design | Year: 2011

We report on selective growth of highly efficient nonlinear optical stilbazolium crystals by using sequential crystal growth in different solvent systems. Stilbazolium-salt crystals DSTMS (N,N-dimethylamino-N′- methylstilbazolium 2,4,6-trimethylbenzenesulfonate) with state-of-the-art nonlinear optical properties exhibit a thin plate-like morphology when grown in methanol and a thick trapezoidal-like morphology when grown in acetonitrile. We demonstrate morphology and thickness control of bulk DSTMS crystals by using sequential crystal growth by choosing a different solvent for growing bulk crystals as for growing seed crystals. For crystals growing in methanol solution from trapezoidal-like seed crystals grown in acetonitrile solution, the average growth rate is similar as in methanol alone, but the specific growth rate is considerably different: the aspect ratio of such crystals may be 1 order of magnitude larger than for crystals growing in methanol alone. For crystals growing in acetonitrile solution from thin plate-like seed crystals grown in methanol solution, the thickness slowly increases, while the lateral size remains similar. Such morphology and thickness control of DSTMS by sequential crystal growth in different solvents is a promising technique for practical applications, where crystals of a certain thickness are desired, for example, for THz-wave generation, frequency conversion, electro-optics, and field detection. © 2011 American Chemical Society. Source

Kim J.-S.,Ajou University | Jeong J.-H.,Ajou University | Yun H.,Ajou University | Jazbinsek M.,Rainbow Photonics AG | And 3 more authors.
Crystal Growth and Design | Year: 2013

We report on new acentric styryl quinolinium crystals with phenolic sulfonate counteranions and investigate their supramolecular interactions that affect their quadratic nonlinear optical properties. The phenolic group acting as an electron-donor as well as hydrogen-bond donor site is located at one end of the anion, while the sulfonate group acting as an electron-acceptor as well as hydrogen-bond acceptor site is located at the opposite end of the anion. New styryl quinolinium crystals with 4-hydroxybenzenesulfonate and 6-hydroxynaphthalene-2-sulfonate counteranions exhibit a large macroscopic optical nonlinearity with very efficient second harmonic generation (SHG) efficiency. In styryl quinolinium 4-hydroxybenzenesulfonate crystals, the styryl quinolinium cation chromophores exhibit an acentric ordering with a high order parameter close to 1.0, which is optimal for electro-optic applications or THz-wave generation. The 4-hydroxybenzenesulfonate counteranions form strong head-to-tail hydrogen bonds, and they are also packed in acentric layers. The direction of the polar axes in cation and anion layers is practically identical. Therefore, the introducing phenolic group acting as an electron-donor as well as hydrogen-bond donor to the sulfonate counteranion is a potential technique for crystal engineering to tailor molecular ordering as well as the physical properties of salt-type quinolinium derivatives. © 2013 American Chemical Society. Source

Vicario C.,Paul Scherrer Institute | Jazbinsek M.,Rainbow Photonics AG | Ovchinnikov A.V.,RAS Joint Institute for High Temperatures | Chefonov O.V.,RAS Joint Institute for High Temperatures | And 4 more authors.
Optics Express | Year: 2015

We investigated Terahertz generation in organic crystals DSTMS, DAST and OH1 directly pumped by a Cr:forsterite laser at central wavelength of 1.25 μm. This pump laser technology provides a laser-to-THz energy conversion efficiency higher than 3 percent. Phase-matching is demonstrated over a broad 0.1-8 THz frequency range. In our simple setup we achieved hundred μJ pulses in tight focus resulting in electric and magnetic field larger than 10 MV/cm and 3 Tesla. ©2015 Optical Society of America. Source

Choi E.-Y.,Ajou University | Choi E.-Y.,Korea Advanced Institute of Science and Technology | Jazbinsek M.,Rainbow Photonics AG | Jeong J.-H.,Ajou University | Kwon O.-P.,Ajou University
CrystEngComm | Year: 2012

We demonstrate a simultaneous crystal growth and purification method by using ionic additives for organic π-conjugated single crystals grown from impure materials, synthesized by the favorable Knoevenagel condensation reactions. The phenolic polyene OH1 (2-(3-(4-hydroxystyryl)-5,5- dimethylcyclohex-2-enylidene)malononitrile) single crystals grown in the presence of ionic organic additives, stilbazolium and pyridinium derivatives, exhibit a higher purity and better optical quality compared to crystals grown in the absence of the additives. © 2012 The Royal Society of Chemistry. Source

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