Show Second Harmonic Generation Research Articles

A folded π-system with supramolecularly oriented dipoles: single-component piezoelectric relaxor with NLO activity.

Organic molecules with an active dipole moment have a natural propensity to align in an antiparallel fashion in the solid state, resulting in zero macroscopic polarization. This primary limitation makes the material unresponsive to switching with electric fields, mechanical forces, and to intense laser light. A single-component organic material that bestows macroscopic dipole-driven electro-mechanical and optical functions, e.g., piezoelectric, ferroelectric and nonlinear optical (NLO) activity, is unprecedented due to the design challenges imparted by crystal symmetry and dipole orientations. Herein we report a crystalline organic material that self-assembles with a polar order (P 1), and is endowed with a high piezoelectric coefficient (d 33-47 pm V-1), as well as ferroelectric and Debye-type relaxor properties. In addition, it shows second harmonic generation (SHG) activity, which is more than five times that of the benchmark potassium dihydrogen phosphate. Piezoelectric force microscopy (PFM) images validated electro-mechanical deformations. Piezoresponse force spectroscopy (PFS) studies confirmed a signature butterfly-like amplitude and a phase loop. To the best of our knowledge, this is the first report of a folded supramolecular π-system that manifests unidirectionally oriented dipoles and exhibits piezoelectricity, ferroelectricity, and has excellent ability to generate second harmonic light. These findings can herald new design possibilities based on folded architectures to explore opto-, electro- and mechano-responsive multifaceted functions.

Structural Variation and Switchable Nonlinear Optical Behavior of Metal-Organic Frameworks.

Two europium metal-organic frameworks (MOFs) based on the same ligand, named as ZJU-23-Eu and ZJU-24-Eu, are selectively synthesized by fine-tuning solvent contents to tailor the coordination modes. Eu atoms are eight-coordinated and nine-coordinated in ZJU-23-Eu and ZJU-24-Eu respectively, and their frameworks vary in both spatial connectivity and symmetry. The ligand not only has multiphoton response but also suitable triplet energy level (19998cm-1 ) to sensitize Eu3+ . Thus ZJU-23-Eu exhibits characteristic emission of Eu3+ peaking at 614nm via the energy transfer from the two-/three-photon excited ligand to Eu3+ , with its bidimensional layered structure benefiting this process. In contrast, the changed spatial connectivity in tridimensional ZJU-24-Eu narrows the distances between adjacent Eu3+ ions and reduces the density, resulting in poor two-photon excited fluorescence. Besides, noncentrosymmetric ZJU-24-Eu shows second harmonic generation (SHG) response with an intensity of ≈6.2 times relative to KH2 PO4 (KDP) microcrystalline powder while centrosymmetric ZJU-23-Eu cannot. These results have established two nonlinear optical (NLO) models based on MOFs to synchronously analyze the effects of two structural variables on different NLO behaviors, and provide ingenious ways to design MOF-based NLO devices with function on demand.

BaV2O6·H2O: A nonlinear optical crystal with a large bandgap

The first Ba-containing hydrated vanadate as nonlinear optical (NLO) material, BaV2O6·H2O, was synthesized by facile hydrothermal method. The single-crystal X-ray diffraction result shows that this compound crystallizes in the acentric orthorhombic space group of P212121 with cell parameters a = 7.3993(6) Å, b = 8.9934(7) Å, and c = 9.7206(8) Å. UV–vis-IR diffuse reflectance spectrum shows that the compound has a large bandgap of 4.60 eV and moderate transparency range. The title compound shows second-harmonic generation (SHG) efficiency about 0.5 times of KH2PO4 (KDP). The structure-property relationship of BaV2O6·H2O was clarified by the first-principles studies.

Cation‐Tuned Synthesis of Fluorooxoborates: Towards Optimal Deep‐Ultraviolet Nonlinear Optical Materials

AbstractThe development of new nonlinear optical (NLO) materials for deep‐ultraviolet (DUV) applications is in great demand. However, the synthesis of an ideal DUV NLO crystal is a serious challenge. Herein, three new alkali‐metal fluorooxoborates, AB4O6F (A=K, Rb, and Cs, and a mixed cation between two of them), were successfully synthesized by cation regulation. It is found that all reported compounds exhibit short UV absorption edges (<190 nm), and show second harmonic generation (SHG) responses ranging from 0.8 to 1.9 KH2PO4 (KDP). Interestingly, by judicious selection of the A‐site alkali‐metal cations, the arrangement of NLO‐active structural units is fine‐tuned to an optimal configuration, which contributes to large SHG responses.

Cation-Tuned Synthesis of Fluorooxoborates: Towards Optimal Deep-Ultraviolet Nonlinear Optical Materials.

The development of new nonlinear optical (NLO) materials for deep-ultraviolet (DUV) applications is in great demand. However, the synthesis of an ideal DUV NLO crystal is a serious challenge. Herein, three new alkali-metal fluorooxoborates, AB4 O6 F (A=K, Rb, and Cs, and a mixed cation between two of them), were successfully synthesized by cation regulation. It is found that all reported compounds exhibit short UV absorption edges (<190 nm), and show second harmonic generation (SHG) responses ranging from 0.8 to 1.9 KH2 PO4 (KDP). Interestingly, by judicious selection of the A-site alkali-metal cations, the arrangement of NLO-active structural units is fine-tuned to an optimal configuration, which contributes to large SHG responses.

Beryllium‐Free β‐Rb2Al2B2O7 as a Possible Deep‐Ultraviolet Nonlinear Optical Material Replacement for KBe2BO3F2

AbstractA new beryllium‐free deep‐ultraviolet (DUV) nonlinear optical (NLO) material, β‐Rb2Al2B2O7 (β‐RABO), has been synthesized and characterized. The chiral nonpolar acentric material shows second‐harmonic generation (SHG) activity at both 1064 and 532 nm with efficiencies of 2×KH2PO4 and 0.4×β‐BaB2O4, respectively, and exhibits a short absorption edge below 200 nm. β‐Rb2Al2B2O7 has a three‐dimensional structure of corner‐shared Al(BO3)3O polyhedra. The discovery of β‐RABO shows that through careful synthesis and characterization, replacement of KBe2BO3F2 (KBBF) by a Be‐free DUV NLO material is possible.

Beryllium-Free β-Rb2 Al2 B2 O7 as a Possible Deep-Ultraviolet Nonlinear Optical Material Replacement for KBe2 BO3 F2.

A new beryllium-free deep-ultraviolet (DUV) nonlinear optical (NLO) material, β-Rb2 Al2 B2 O7 (β-RABO), has been synthesized and characterized. The chiral nonpolar acentric material shows second-harmonic generation (SHG) activity at both 1064 and 532 nm with efficiencies of 2×KH2 PO4 and 0.4×β-BaB2 O4 , respectively, and exhibits a short absorption edge below 200 nm. β-Rb2 Al2 B2 O7 has a three-dimensional structure of corner-shared Al(BO3 )3 O polyhedra. The discovery of β-RABO shows that through careful synthesis and characterization, replacement of KBe2 BO3 F2 (KBBF) by a Be-free DUV NLO material is possible.

Enhancement of nonlinear optical property in ZnS PVA films due to self-assembly

Nanostructured zinc sulfide ( ZnS ) thin films were synthesized in polyvinyl alcohol matrix by chemical bath deposition and self-assembly techniques. ZnS nanostructured thin films show second harmonic generation (SHG) under irradiation with a pico-second Nd :YAG laser system and the second harmonic intensity is higher for self-assembled nanotree like structured ZnS thin film in comparison with that from chemical bath deposited thin film. Under nanosecond laser pulses, thin films possess good saturable absorption behavior. The optical bandgap and visible luminescence also get enhanced.

Helical silver(I) coordination polymer with oxazoline-containing ligand: Structure, non-linear and ferroelectric property

A new coordination polymer [Ag4(dob)4(BF4)4] (1) was synthesized by reaction of rigid ligand 1,3-di(2-oxazolinyl)benzene (dob) with silver(I) tetrafluoroborate and characterized by elemental analysis, single crystal X-ray diffraction and electrospray mass spectrometry. The complex has one-dimensional (1D) helical chain structure which is further linked together by Ag⋯F and hydrogen bonding interactions to form a three-dimensional (3D) supramolecular structure. Complex 1 crystallizes in the noncentrosymmetrical space group and shows second harmonic generation (SHG) and ferroelectric property.

Second-Harmonic Generation in Thermally Poled Na2O-Al2O3-TeO2 Glasses

Tellurite glasses exhibit attractive optical properties such as high refractive index, high transmittance in the infrared-to-visible region, and large third-order nonlinear susceptibility. Poled tellurite glasses also show second-harmonic generation (SHG) as revealed by the present authors. However, there exist many unresolved problems in second-harmonic generation of oxide glasses; SH intensity is low and it decays at room temperature. In this work, the effect of Al2O3 addition on SH intensity and its decay has been explored for thermally poled sodium tellurite glasses. The decay rate of SH intensity is reduced by the addition of Al2O3. The result is similar to those reported for phosphate and silicate glasses containing Al2O3. Also, the glasses poled at a voltage of 4 kV manifest optimum poling temperature lower than that for the same glasses poled at 3 kV.

N‐(3,5‐Di‐tert‐butylsalicylidene)‐4‐iodobenzene, a peculiar case of a nonlinear optical photoswitch

AbstractN‐(3,5‐Di‐tert‐butylsalicylidene)‐4‐iodobenzene (1) is photochromic in the solid state, owing to its ability to yield enol–keto tautomerism. Despite its centrosymmetric structure (P21/c), polycrystalline thin films of 1 show second harmonic generation (SHG). Moreover, this SHG can be reversibly switched by light. Investigations using confocal microscopy showed that a morphology change occurs when the fundamental beam of a Ti:sapphire (990 nm, 1.3 ps) is focused on the material, yielding an SHG‐active solid. Copyright © 2007 John Wiley &amp; Sons, Ltd.

( E)-4-[2-(bis(octadecylsulfanyl)tetrathiafulvalenyl)ethenyl]-1-methylpyridinium iodide: synthesis and characterisation of its Langmuir–Blodgett films

Langmuir–Blodgett (LB) monolayers of ( E)-4-[2-(bis(octadecylsulfanyl)tetrathiafulvalenyl)ethenyl]-1-methylpyridinium iodide exhibit an area of 0.53±0.04 nm 2 molecule −1 in contact with the substrate and a thickness of 2.1±0.04 nm, the dimensions being derived from the frequency change when deposited onto a 10-MHz quartz crystal and the surface plasmon resonance data, respectively. The molecules are non-centrosymmetrically aligned, and thus the films show second-harmonic generation (SHG) and have an effective susceptibility of 70 pm V −1 at 1.064 μm.

Synthesis, characterization, Langmuir-Blodgett film-forming properties, and second-harmonic-generation studies of ruthenium(II) complexes with long hydrocarbon chains.

Several ruthenium(II) surfactants of general formula [Ru(bpy)(2)L](2+) [L = N-(2-pyridylmethylene)-3,4-bis(tetradecyloxy)benzenamine, N-(2-pyridylmethylene)-3,4-bis(octadecyloxy)benzenamine, 9-(3,4-bis(tetradecyloxy)benzenamino)-4,5-diazafluorene, 9-(4-(tetradecyloxy)-4'-azabenzenamino)-4,5-diazafluorene, 4,7-dinonadecyl-1,10-phenanthroline] and [Ru(L)(3)](2+) (L = 4,7-dinonadecyl-1,10-phenanthroline) were synthesized and characterized by elemental analysis, (1)H NMR, UV-vis, luminescence spectroscopy, and cyclic voltammetry. Their Langmuir-Blodgett (LB) film formation properties and surface pressure-area (pi-A) isotherms were also studied. Two complexes were found to show second-harmonic-generation (SHG) behavior.

Fluorescence study on a liquid-crystalline polyester containing naphthoate mesogen units

Using fluorescence spectroscopy, we investigated intermolecular interaction between mesogenic units in a thermotropic main-chain LC polyester, P(HBA73/HNA27), containing oxybenzoate (HBA) and oxynaphthoate (HNA) mesogenic units. It is known that P(HBA73/HNA27), which has a high molecular weight, shows second harmonic generation (SHG) activity. P(HBA73/HNA27) showed fluorescence at 410 nm and 430 nm, originating from two kinds of intermolecular interaction. Fluorescence with a peak at 410 nm comes from the ground-state complex between partially overlapping naphthoate units or between naphthoate and oxybenzoate units whose interaction is weak. Fluorescence at 430 nm comes from the ground-state complex between fully overlapping naphthoate units whose interaction is strong. The relative fluorescence intensity for 430 nm compared to 410 nm increases with increases in inherent viscosity, ηinh, of P(HBA73/HNA27), the composition ratio of HNA/HBA, and temperature. The fluorescence intensity ratio, I430/I410, of P(HBA73/HNA27) shows the same inherent-viscosity dependence with its sudden increase at ηinh = 1.4 ∽ 2.2 dL/g as its SHG activity does, supporting the polar structure and uniformity of LC orientation of the present LC polyester. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2922–2928, 2000

A tetrahedral coordination compound for second-order nonlinear optics: synthesis, crystal structure and SHG of Zn(2-NH 2py) 2Cl 2

A coordination compound with a tetrahedral molecular configuration, Zn(NH 2py) 2Cl 2(2-NH 2py=2-aminopyridine), was prepared. It is transparent in the visible region and shows second harmonic generation (SHG) effect 8.0 times as strong as that of KDP. X-ray single crystal structure analysis reveals that all Zn(NH 2py) 2Cl 2 molecules are aligned in a fully parallel direction. The advantages and disadvantages of tetrahedral zinc coordination compounds as nonlinear optical (NLO) materials are discussed. The results may represent a novel strategy for designing a new class of transparent NLO materials.

Centrosymmetric Chromophores: Second-Harmonic Generation from Langmuir−Blodgett and Spun-Coated Films of Hydroxy-Substituted Squaraines

The linear and nonlinear optical properties of 2,4-bis[4-(N-methyl-N-alkylamino)-2,6-dihydroxyphenyl]-squaraine (1), 2,4-bis[4-(N,N-dialkylamino)-2-hydroxyphenyl]squaraine (II), and 2,4-bis(8-hydroxy-9-julolidinyl)squaraine (III) are reported. Electrospray ionization mass spectrometry (ESI-MS) has provided evidence of association in dilute solution (ca. 2 x 10 -5 mol dm -3 ) with m/z values which may be assigned to dimeric aggregates for dye II. Solid solutions of this dye in poly(vinyl acetate) show second-harmonic generation (SHG), albeit very weak, and therefore indicate that the dimeric aggregate is noncentrosymmetric. In contrast, dyes I and III form heptameric aggregates with their solid solutions being SHG-inactive. There is some correlation between the type of aggregate from ESI-MS and the Langmuir film spectra, but van der Waals interactions between the hydrophobic groups play a more significant role in determining the structure at the air-water interface. The absorption maxima of the Langmuir and deposited Langmuir-Blodgett films vary from 530 nm to the near-infrared, but only those films with a maximum at 650- 700 nm, or a significant shoulder in this range, are SHG-active. The second-order behavior is not an inherent property of the molecule itself but, instead, is a result of intermolecular effects and is dependent upon the noncentrosymmetry of the aggregate and the film.

Langmuir-Blodgett films for nonlinear optical applications

Azo-benzene chromophores with an oxygen donor and five different end-groups have been attached to octadecyl chains or to polysiloxane backbones via hexadecyl spacer groups. These were deposited by the Langmuir-Blodgett (LB) technique using our own design of diamond-barrier trough. The LB deposition properties of the polymers were superior to those of the low molecular mass materials, which did not show second harmonic generation (SHG) as deposited monolayers. The strength of SHG from the polymers correlated with acceptor strength, but the maximum signal was only about 10% of that of hemicyanine. Only one of the polymers gave thick films of very high quality; this had a hydroxyl end-group and showed no SHG except when deposited from an acid subphase. This was presumed to result from protonation of the azo group to create an acceptor. The quality of the deposited films may correlate with their phase behaviour; the best material showed only a presumed soft crystalline phase. The film-forming properties of that film were remarkable; loss figures of around 2.5 dB cm−1 have been recorded at 633 nm in films of 1.3 Μm thickness. Future work will seek to isolate and independently control the factors involved in good film formation and in high SHG.