SHG Response Research Articles

A chirally helical coordination polymer self-assembled with the ligand 2-(2-carboxyphenyl)imidazo(4,5-f)(1,10)phenanthroline: crystal structure, SHG response and tunable photoluminescence

A chirally helical coordination polymer [Zn(H2O)(ONCP)Cl]n self-assembled with ligand 2-(2-carboxyphenyl)imidazo(4,5-f)(1,10)phenanthroline displays second harmonic generation efficiency, which is approximately two times as much as that of potassium dihydrogen phosphate (KDP), and tunable photoluminescence images form yellow-green to white based on the variation of excitation light.

Pb2B5O9I: An Iodide Borate with Strong Second Harmonic Generation

The combination of lone-pair effects on Pb(2+) cations and the smaller electronegativity of I(-) anions into the pentaborate framework generates a phase-matchable material, Pb(2)B(5)O(9)I, with the largest powder SHG response among borates, about 13.5 times that of KDP (KH(2)PO(4)), and transparency over the near-UV to middle-IR region. DFT calculations on electronic structure and cutoff-energy-dependent SHG coefficients confirm these origins.

Mapping of the organization of p-nitroaniline in SAPO-5 by second-harmonic generation microscopy

Second-harmonic generation microscopy (SHGM) has been employed to study crystals of zeolite-like material SAPO-5 filled with p-nitroaniline (PNA). The SHG and 2-photon fluorescence response of PNA in the one-dimensional channels readily reveals the pore accessibility; intergrown crystallites containing hexagonal pyramidal components and internal diffusion barriers are found next to seemingly perfect crystals. The sensitivity of second-harmonic generation to molecular orientation allowed for mapping of the domains of differently organized PNA. Dense domains of highly aligned PNA alternate with dilute zones with loosely aligned PNA.

Syntheses, crystal structures, and properties of three new lanthanum(iii) vanadium iodates

Systematic explorations of new compounds in the La(3+)-V(4+)/V(5+)-iodate system led to three new lanthanum(III) vanadium iodates, namely, LaVO(IO(3))(5), LaV(2)O(6)(IO(3)), and LaVO(2)(IO(3))(4).H(2)O. LaVO(IO(3))(5) is isostructural with LaTiO(IO(3))(5) and its structure contains a 0D [VO(IO(3))(5)](3-) anionic unit composed of one VO(6) octahedron linked to five IO(3)(-) groups. Such 0D anionic units are separated by La(3+) ions. LaV(2)O(6)(IO(3)) exhibits a unique 3D framework composed of 1D [V(2)O(6)](2-) ladder like chains and 2D [La(IO(3))](2+) layers. LaVO(2)(IO(3))(4).H(2)O is isostructural with LnMoO(2)(IO(3))(4)(OH) (Ln = La, Nd, Sm, Eu) with a polar space group P2(1), its structure contains a novel 0D [VO(2)(IO(3))(4)](3-) anionic unit composed of one VO(6) octahedron linked with four IO(3)(-) groups and two terminal O(2-) anions. Such 0D anionic units are separated by La(3+) ions. The structure of LaVO(2)(IO(3))(4).H(2)O can also be described as the 8-MR channels of the 3D [La(IO(3))(4)](-) anion being filled by the VO(6) octahedra and lattice water molecules. LaVO(2)(IO(3))(4).H(2)O displays a weak SHG response of about 0.2 times that of KDP. Optical, thermal stability and magnetic susceptibility measurements as well as theoretical calculations have also been performed.

Crystal structure, crystal growth and characterization of novel organic NLO material: 2,4,4′-Trimethoxybenzophenone

Single crystals of 2,4,4′-Trimethoxybenzophenone (TMB) were grown by slow evaporation solution growth technique using acetone as a solvent. TMB crystallizes in monoclinic system with noncentrosymmetric space group, P2 1, and the cell parameters are a = 8.485(5) Å, b = 8.173(5) Å, c = 10.254(5) Å, β = 102.085(5)° and V = 695.3(7) Å 3. Gaussian 98W has been used to calculate the first-order hyperpolarizability of TMB. Fourier transform infrared (FTIR) spectroscopic studies were performed for the identification of different modes present in the compound. TMB crystals are transparent in the entire visible region and have a lower optical cutoff at 400 nm. The powder second harmonic generation efficiency of TMB was determined to be 6 times that of urea. The observed SHG response for TMB is due to effective charge transfer arising from the donor–π–acceptor–π–donor (D–π–A–π–D) structure of the molecule. From the thermogravimetric/differential thermal analysis, the TMB was found to be thermally stable up to 79 °C. The dielectric and mechanical properties of the TMB were also studied.

BaNbO(IO3)5: A New Polar Material with a Very Large SHG Response

By combination of Nb(5+) (having a d(0) electronic configuration) and the lone-pair-containing iodate anion, a new SHG material, BaNbO(IO(3))(5), has been prepared. It exhibits a very large SHG response (approximately 14 times that of KH(2)PO(4) and approximately 660 times that of alpha-SiO(2)) and is phase-matchable. The material has high thermal stability and a wide transparent region.

Observation of steric hindrance effect controlling crystal packing structures and physical properties in three new isomeric nitronyl nitroxide radicals

Three isomeric nitronyl nitroxide radical compounds, 2-[ n-( N-benzyl)pyridinium]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide bromide ( n = 2, 3 and 4 for 1, 2 and 3, respectively), have been synthesized and structurally characterized. The influence of steric hindrance on the molecular packing structures and physical properties has been observed. In the radical 1, such steric hindrance leads to a folding conformation of the imidazoline and benzene rings and the intramolecular C–H…π interaction between the methyl group and the benzene ring. There is no such effect in 2 and 3. In crystal of 2, there are the intermolecular C–H…π between methyl groups and benzene ring and intermolecular π…π stacking interaction between pyridine and benzene rings. Crystal of 2 with a chiral space group P2 12 12 1 shows the SHG response about 0.4 times as that of urea. In crystal of 3, there are three symmetry-independent radical molecules, which form an unusually six-membered supramolecular ring via intermolecular O…π interactions. For the solid sample of 3, the X-band EPR exhibits an axially symmetric signal and magnetic susceptibility data suggest intermolecular antiferromagnetic (AFM) coupling interactions and very weak intermolecular ferromagnetic (FM) coupling interactions which is more likely caused by magnetic anisotropy, while measurements of both 1 and 2 show isotropic X-band EPR signals and simple Currie–Weiss magnetic behavior.

Two d10 coordination polymers based on 4,4′-(hexafluoroisopropylidene)diphthalic acid: Syntheses, structures and physical properties

Two novel coordination polymers, [Zn 2 (FA)(4,4′-bipy) 2 ]·8H 2 O ( 1 ) and Cd 2 (FA)(2,2′-bipy) ( 2 ), have been synthesized under hydrothermal conditions, and their structures were determined by single-crystal X-ray diffraction. Polymer 1 features an unusual three-dimensional (3D) network with (4.6 2 .8 3 )(4 2 .6 2 .8 2 ) topology. Polymer 2 has a complicated 3D framework which displays a strong SHG response and ferroelectric properties. Two novel coordination polymers, [Zn 2 (FA)(4,4′-bipy) 2 ]·2H 2 O ( 1 ) and Cd 2 (FA)(2,2′-bipy) ( 2 ), (H 4 FA = 4,4′-(hexafluoroisopropylidene)diphthalic acid, 4,4′-bipy = 4,4′-bipyridine, 2,2′-bipy = 2,2′-bipyridine), have been synthesized under hydrothermal conditions, and their structures were determined by single-crystal X-ray diffraction. Polymer 1 features an unusual three-dimensional (3D) network with (4 · 6 2 · 8 3 )(4 2 · 6 2 · 8 2 ) topology. Polymer 2 has a complicated 3D framework and crystallizes in non-centrosymmetric space group ( Fdd 2) belonging to polar point group ( C 2 v ), which displays a strong SHG response and ferroelectric properties. Moreover, the luminescent properties of 1 and 2 have also been investigated.

Synthesis, crystal growth, characterization and structure–NLO property relationship in 1,3-bis(4-methoxyphenyl)prop-2-en-1-one single crystal

High-quality single crystals of 1,3-bis(4-methoxyphenyl)prop-2-en-1-one (BMP) of size 20 mm×16 mm×5 mm have been grown by the slow evaporation of an acetone solution at 28 °C and characterized by elemental analysis, thermo-gravimetric analysis/differential thermal analysis (TGA/DTA), Fourier transform infrared (FTIR) spectroscopy and single-crystal X-ray diffraction. BMP crystallizes in the orthorhombic system with the noncentrosymmetric space group P2 12 12 1. The crystal melts at 107 °C and the average Vickers hardness number is 17 kg mm −2. BMP crystals are transparent in the entire visible region and have a lower optical cutoff at 435 nm. A Kurtz powder second harmonic generation (PSHG) measurement indicated that BMP and urea have similar responses. The observed SHG response for BMP is due to effective charge transfer arising from the donor– π-acceptor– π-donor ( D– π– A– π– D) structure of the molecule and the weak C–H… π interaction observed in the crystal structure, which helps to stack the molecules in a noncentrosymmetric arrangement.

Isotope Effect on SHG Response and Ferroelectric Properties of a Homochiral Zinc Coordination Compound Containing Tetrazole Ligand

Hydrothermal treatment of a solution of water or deuterium oxide containing N-4-cyanobenzylcinchonidine bromide (CBCBr), NaN3, and Zn(NO3)2·6H2O at 105 °C gave the respective in situ [2 + 3] cycloaddition products (TBC-N4)2Zn(N3)4(X2O) (1, X = H; 2, X = D; CBC-N4 = N-4-tetrazoylbenzylcinchonidine). A study of the SHG, ferroelectric, and permittivity properties of these novel metal-coordination compounds (MCCs) revealed huge deuterated effects (DEF) on SHG (5-fold increase), ferroelectric activity (31% increase), and dielectric behavior (up to 830% increase) upon deuterium substitution from 1 to 2. As expected, the dielectric constants in both dehydrated 1 and dedeuterated 2 are comparable and the DEF is observed to disappear with increasing temperature.

Application of the anisotropic bond model to second-harmonic generation from amorphous media

As a step toward analyzing second-harmonic generation (SHG) from crystalline Si nanospheres in glass, we develop an anisotropic bond model (ABM) that expresses SHG in terms of physically meaningful parameters and provide a detailed understanding of the basic physics of SHG on the atomic scale. Nonlinear-optical (NLO) responses are calculated classically via the four fundamental steps of optics: evaluate the local field at a given bond site, solve the force equation for the acceleration of the charge, calculate the resulting radiation, then superpose the radiation from all charges. Because the emerging NLO signals are orders of magnitude weaker and occur at wavelengths different from that of the pump beam, these steps are independent. Paradoxically, the treatment of NLO is therefore simpler than that of linear optics (LO), where these calculations must be done self-consistently. The ABM goes beyond previous bond models by including the complete set of underlying contributions: retardation (RD), spatial-dispersion (SD), and magnetic (MG) effects, in addition to the anharmonic restoring force acting on the bond charge. Transverse as well as longitudinal motion is also considered. We apply the ABM to obtain analytic expressions for SHG from amorphous materials under Gaussian-beam excitation. These materials represent an interesting test case not only because they are ubiquitous but also because the anharmonic-force contribution that dominates the SHG response of crystalline materials and ordered interfaces vanishes by symmetry. The remaining contributions, and hence the SHG signals, are entirely functions of the LO response and beam geometry, so the only new information available is the anisotropy of the LO response at the bond level. The RD, SD, and MG contributions are all of the same order of magnitude, so none can be ignored. Diffraction is important in determining not only the pattern of the emerging beam but also the phases and amplitudes of the different terms. The plane-wave expansion that gives rise to electric quadrupole magnetic dipole effects in LO appears here as retardation. Using the paraxial-ray approximation, we reduce the results to the isotropic case in two limits, that where the linear restoring force dominates (glasses) and that where it is absent (metals). Both forward- and backscattering geometries are discussed. Estimated signal strengths and conversion efficiencies for fused silica appear to be in general agreement with data where available. Predictions that allow additional critical tests of these results are made.

The first metal–organic framework (MOF) of Imazethapyr and its SHG, piezoelectric and ferroelectric properties

Hydrothermal reaction of H-Imazethapyr (2-(4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl)-5-ethyl-3-pyridinecarboxylic acid) with Cd(ClO4)2.6H2O offers a diamond-like MOF Cd(Imazethapyr)2 in which it crystallizes in a non-centrosymmetric space group (Fdd2) belonging to polar point group (C2v). MOF displays a strong SHG response, and good ferroelectric and piezoelectric properties.

Phase matching considerations in second harmonic generation from tissues: Effects on emission directionality, conversion efficiency and observed morphology

We present a heuristic treatment which relates SHG image intensities, signal directionality, and observed morphology to the physical structure of collagen and cellulose fibrillar tissues. The SHG creation model is based upon relaxed phase matching conditions which account for dispersion, randomness, and axial momentum contributions from the media, and includes a mathematical treatment which relates SHG conversion efficiency to fibril diameter and packing through the inclusion of potential intensity amplification resultant from quasi-phase matching (QPM). A direct consequence of this theory is that SHG in biological tissues is not strictly a coherent process, and that the forward directed SHG has a longer coherence length than the backward component, Through this treatment, we show that the emission directionality and also conversion efficiency do not arise solely from the fibril size but also depend on packing density and order of the inter-fibril structure. We demonstrate these principles in comparing the SHG response in normal and Osteogenesis Imperfecta (OI) skin. We show that the observed directionality and decreased relative intensity in the diseased state is consistent with phase matching conditions arising from the decreased fibril size and more random assembly. We further use this theory to explain the differences in morphology seen in forward and backward collected SHG in fibrillar tissues (e.g., collagenous and cellulosic). Specifically, we attribute segmented appearance to destructive interference between small fibrils separated by less than the coherence length. We suggest the approach based on relaxed phasematching conditions is general in predicting the SHG response in tissues and may be broadly applicable in interpreting the SHG contrast for diagnostic applications.

LiMoO3(IO3): A New Molybdenyl Iodate Based on WO3‐Type Sheets with Large SHG Response.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Probing the Interfacial Structure of Aqueous Electrolytes with Femtosecond Second Harmonic Generation Spectroscopy

The existence of polarizable anions at the outermost layer of electrolyte solutions has received much recent attention from both theory and experiment, but remains controversial. Anions can be probed directly in the UV via their strong charge-transfer-to-solvent (CTTS) transitions. We have recently described experimental characterizations of enhanced concentrations of several anions at the air-water interface, using the surface-specific technique of second harmonic generation. Here we present a detailed description of the experimental design and methodology used in these experiments, as well as a proof of principle experiment with the known surfactant tetrabutylammonium iodide (TBAI), yielding surface enhancements in excellent agreement with surface tension measurements. Furthermore, we analyze the observed increase in the nonresonant contribution to the SHG response from the water background of alkali halide solutions. The observed change in the water structure of alkali halide (except iodide) solutions is linear in concentration and correlates with the fractional saturation concentration of the salt and with the ionic volume fraction. Finally, the surface adsorption of iodide at high bulk concentrations is analyzed, but it is not possible to differentiate between a Gibbs free energy of adsorption of zero (surface concentration proportional to the bulk) or -0.8 kcal/mol, as predicted by recent molecular dynamics simulations.

Structural, morphological, optical, and nonlinear optical properties of fluorine‐doped zinc oxide thin films deposited on glass substrates by the chemical spray technique

AbstractFluorine‐doped zinc oxide thin films (ZnO:F) were deposited on sodocalcic glass substrates from an aged solution using a chemical spray technique. The effect of substrate temperature (T S) on the morphological, optical, and nonlinear optical (NLO) properties of the ZnO:F thin films was studied. These films were analysed using X‐ray diffraction, scanning electron microscopy, profilometry, optical transmittance, optical fluorescence, and second (SHG) and third harmonic generation (THG) techniques. A polycrystalline structure with a preferential growth along the ZnO(002) plane was found in all cases, with a corresponding average crystal size of less than 32 nm for the films. The morphology of the surfaces and some optical properties were found to be dependent on T S. The films deposited at low T S (400 °C) showed a uniform surface covered with needle‐like grains as well as SHG and THG response. In contrast, for the films deposited at 525 °C, a porous surface with irregular‐shaped grains was obtained and a substantial reduction of the SHG and THG response was detected. NLO χ (2)eff coefficients one order of magnitude larger than the χ (2)11 component of an α‐quartz reference crystal were measured for all ZnO:F thin films. The χ (3) values of the samples, under resonant conditions, were in the interesting range of 10–12 esu. Finally, a typical optical transmittance higher than 85% and a band gap (E g) of 3.4 eV were evaluated for films deposited under optimal conditions. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

LiMoO 3(IO 3): A new molybdenyl iodate based on WO 3-type sheets with large SHG response

A novel lithium molybdenyl iodate, LiMoO 3(IO 3), has been prepared by hydrothermal reactions at 170 °C. Its crystal structure has been determined from single-crystal X-ray data: space group P2 1, a = 5.4104(4) Å, b = 5.3158(3) Å, c = 9.0025(7) Å, β = 106.863(6)°, Z = 2. LiMoO 3(IO 3) is a new layered material containing [ Mo O 3 ( I O 3 ) ] 1 − anionic layers separated by Li + cations. The anionic layer has an unprecedented configuration consisting of WO 3-type sheets “capped” by IO 3 − groups. The iodate groups have their stereochemically active nonbonded electron pairs align along the b-axis, which creates the polarity in the structure. Second-harmonic-generation measurements on LiMoO 3(IO 3) display a response of about 4 × KH 2PO 4. DTA measurements demonstrate that LiMoO 3(IO 3) is stable up to at least 430 °C. UV–vis diffuse reflectance spectrum of this compound shows a high degree of transparency from 1.1 to 2.8 eV and a band gap of about 2.8 eV.

Designing effective nonlinear optical (NLO) materials with chiral substituents

The experimental strategies and theoretical understanding in transforming molecular conformations with good SHG response functions into polymers with the help of chiral groups are discussed. Chirality plays an important role in designing new types of stable second-order NLO materials. The presence of chiral molecules in the main chain of the polymer introduces acentric conformations and thereby increases the SHG efficiency. On the other hand, for strong donor and acceptor groups between a pi-bridge, large SHG coefficients can be realized at the molecular scale. Chiral molecules are noncentrosymmetric with a nonvanishing electric-dipole-allowed second-order response, which persists in bulk samples also. On the other hand, contributions of magnetic-dipole interactions, which can be strong in chiral materials, allow second-order processes in centrosymmetric materials. Also the polymers incorporated with chiral molecules showed higher response than the standard MNA. This could be due to the chiral component contribution to the electric and magnetic-dipole tensor.

Correlation of large SHG responses with structural characterization in borophosphate niobium glasses

Abstract Transparent and homogeneous sodium borophosphate niobium glasses with good optical quality were obtained for Nb2O5 proportion up to 50 mol%. Large NLO second-order susceptibilities, up to ∼5 pm/V for the highest niobium loading, are generated through an efficient thermal poling process which induces a strong space-charge migration of Na+ cations. From combined IR, Raman and thermal analyses, we establish that the observed strong increase of χ(2) responses with niobium concentration is linked to the extent of the niobium–oxygen 3D structure which enhances the third-order susceptibility.

1D Helix, 2D Brick-Wall and Herringbone, and 3D Interpenetration d10 Metal−Organic Framework Structures Assembled from Pyridine-2,6-dicarboxylic Acid N-Oxide

Five novel interesting d(10) metal coordination polymers, [Zn(PDCO)(H2O)2]n (PDCO = pyridine-2,6-dicarboxylic acid N-oxide) (1), [Zn2(PDCO)2(4,4'-bpy)2(H2O)2.3H2O]n (bpy = bipyridine) (2), [Zn(PDCO)(bix)]n (bix = 1,4-bis(imidazol-1-ylmethyl)benzene) (3), [Zn(PDCO)(bbi).0.5H2O]n (bbi = 1,1'-(1,4-butanediyl)bis(imidazole)) (4), and [Cd(PDCO)(bix)(1.5).1.5H2O]n (5), have been synthesized under hydrothermal conditions and structurally characterized. Polymer 1 possesses a one-dimensional (1D) helical chainlike structure with 4(1) helices running along the c-axis with a pitch of 10.090 Angstroms. Polymer 2 has an infinite chiral two-dimensional (2D) brick-wall-like layer structure in the ac plane built from achiral components, while both 3 and 4 exhibit an infinite 2D herringbone architecture, respectively extended in the ac and ab plane. Polymer 5 features a most remarkable and unique three-dimensional (3D) porous framework with 2-fold interpenetration related by symmetry, which contains channels in the b and c directions, both distributed in a rectangular grid fashion. Compounds 1-5, with systematic variation in dimensionality from 1D to 2D to 3D, are the first examples of d(10) metal coordination polymers into which pyridinedicarboxylic acid N-oxide has been introduced. In addition, polymers 1, 4, and 5 display strong blue fluorescent emissions in the solid state. Polymer 3 exhibits a strong SHG response, estimated to be approximately 0.9 times that of urea.