Second-order Nonlinear Optical Films Research Articles

Synthesis and Characterization of Novel Second-Order Nonlinear Optical Chromophore with Multi-Hydroxyl Groups Donor

ABSTRACTNew electro optical chromophore with 4-(bis(2-hydroxyethyl)amino)-2,6-dipropoxybenzaldehyde as electron donor was synthesized and characterized by 1H NMR spectra and mass spectra. Four hydroxyl groups were introduced to the electron donor, which could be easily reacting with carboxyl, isocyanate, anhydride, and so on, to afford us second-order nonlinear optical polymers. Chromophore T showed us good solubility in common solvents, thermal stability (above 200°C) and expected Uv-vis absorption. In this article, polymethyl methacrylate (PMMA) doped with chromophore T at different loading density was prepared to second- order nonlinear optical films by spin coating. These films showed us large second-order nonlinear optical coefficients, 13.5, 19.7, 24.3, and 26.4 pm/V for the second-order nonlinear optical films with chromophore loading density of 10 wt%, 20 wt%, 30 wt%, and 40 wt%, respectively.

Synthesis of novel two-dimensional spindle-type fluorinated nonlinear optical chromophores

Two novel two-dimensional spindle-type fluorinated chromophores with fluorinated phenyl as side groups connecting to the π conjugated bridge were prepared for second-order nonlinear optical applications. The detailed synthetic procedure was reported. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) revealed that the spindle-type fluorinated chromophores have excellent thermal stability. Host–guest doped materials had been used to prepare the second-order nonlinear optical films. The nonlinear electro-optic (EO) coefficient of the poled films was measured by Teng–Man technique at the fundamental wavelength of 1310 nm, and the r 33 up to 28 pm/V was achieved.

Electric-field-induced layer-by-layer fabrication of inorganic–organic hybrid second-order nonlinear optical films

This work focused on the development of a novel method for molecular level assembly and processing of inorganic–organic hybrid second-order nonlinear optical (SONLO) multilayer films. Aromatic diazo group linked silicon sol was first synthesized and used as a polycation. This oligomer was assembled into inorganic–organic hybrid SONLO multilayer films by electric-field-induced layer-by-layer assembly technique with a low molecular weight chromophore molecule as an anion. After UV irradiation, the electrostatic interaction between layers converted to covalent bonds. Large second-harmonic generation signal of the assembled film was observed, which confirmed that the chromophore in the film had a high degree of molecular orientation as assembled under the electric field. As the cross-linked structure and silicon oxygen meshwork in the films, the resulting inorganic–organic hybrid multilayer films displayed good thermal and chemical stability, and excellent NLO properties.

Fabrication of photo-cross-linked stable organic–inorganic hybrid second-order nonlinear optical films

A photo-cross-linked stable organic–inorganic hybrid second-order nonlinear optical (NLO) film was fabricated by sol–gel process with silicon sol linking aromatic diazonium group (SOD) and Chromophore molecule 2-({4-[4-(2-carboxy-2-cyano-vinyl)-phenylazo]-phenyl}-methyl-amino)-ethyl acid (DRCB). The films were poled under 50 DC voltage electric field at room temperature at the existence of solvents. After the solvents volatilized completely and upon UV irradiation under the electric field, the ionic bonds converted to stable covalent bonds in the system, the orientations of the chromophores were fixed by the photo-cross-linked structures. The order parameter of the fabricated film can retain 99% after 17 days at room temperature. The stable organic–inorganic hybrid photo-cross-linked NLO films fabricated in this paper had large potential to be applied in electric-optic devices.

Layer-by-Layer Deposited Organic/Inorganic Hybrid Multilayer Films Containing Noncentrosymmetrically Orientated Azobenzene Chromophores

Organic/inorganic hybrid multilayer films with noncentrosymmetrically orientated azobenzene chromophores were fabricated by the sequential deposition of ZrO2 layers by a surface sol-gel process and subsequent layer-by-layer (LbL) adsorption of the nonlinear optical (NLO)-active azobenzene-containing polyanion PAC-azoBNS and poly(diallyldimethylammonium chloride) (PDDA). Noncentrosymmetric orientation of the NLO-active azobenzene chromophores was achieved because of the strong repulsion between the negatively charged ZrO(2) and the sulfonate groups of the azobenzene chromophore in PAC-azoBNS. Regular deposition of ZrO(2)/PAC-azoBNS/PDDA multilayer films was verified by UV-vis absorption spectroscopy and quartz crystal microbalance measurements. Both UV-vis absorption spectroscopy and transmission second harmonic generation (SHG) measurements confirmed the noncentrosymmetric orientation of the azobenzene chromophores in the as-prepared ZrO2/PAC-azoBNS/PDDA multilayer films. The square root of the SHG signal (I(2omega)(1/2)) increases with the increase of the azobenzene graft ratio in PAC-azoBNS as the number of deposition cycles of the ZrO(2)/PAC-azoBNS/PDDA films remains the same, while the second-order susceptibility chi(zzz)(2) of the film decreases with the increase of the azobenzene graft ratio. Furthermore, the present method was successfully extended to realize the noncentrosymmetric orientation of azobenzene chromophores in multilayer films when small organic azobenzene compounds with carboxylic acid and/or hydroxyl groups at one end and sulfonate groups at the other end were used. The present method was characterized by its simplicity and flexibility in film preparation, and it is anticipated to be a facile way to fabricate second-order nonlinear optical film materials.

Novel Hybrid Covalent / Ionic Self-Assembly Technique for Improved Second-Order Nonlinear Optical Films

ABSTRACTIonically self-assembled monolayer (ISAM) films have been shown to spontaneously produce noncentrosymmetric ordering that gives rise to a substantial second order nonlinear optical (NLO) response. Typically, the ISAM films for NLO response are an assemblage of bilayers of oppositely charged polymers whose thickness can be controlled through variation of pH and ionic strength of the immersion solutions. Here, we investigate the effects of replacing the NLO-active polymer layers with layers of monomeric chromophores containing ionic and covalent bonding sites. Films fabricated exclusively using polyelectrolytes contain some fraction of both randomly oriented and anti-parallel oriented chromophores. We have examined the incorporation of monomeric chromophores into ISAM films in order to increase the net polar orientation of the chromophores and reduce bilayer thickness.

Second-harmonic generation in poled organic monomeric glasses

Novel second-order nonlinear optical films are prepared from glasses of two organic compounds, (S)-2-N-α-(methylbenzylamino)-5-nitropyridine and 2-N-(cyclooctylamino)-5-nitropyridine, cooled rapidly from the isotropic liquid above the melting point. Extremely slow crystallization in the vicinity of the glass transition temperature Tg permits a polar orientation of these organic molecules under high electric fields at temperatures above Tg. Subsequent cooling to temperatures below Tg freezes in the polarization. A maximum value of the d33 nonlinear susceptibility of 7.5 pm/V and reasonable waveguiding properties are obtained. The poling dynamics of these organic glasses near Tg as monitored by second-harmonic generation exhibit a typical William–Landel–Ferry temperature dependence that is identical to their dielectric relaxation characteristics.