Nonlinear Optical Dye Research Articles

Anisotropy in Third-Order Nonlinear Optical Susceptibility ofa Squarylium Dye in a Nematic Liquid Crystal

A squarylium dye is dissolved in 4-cyano-4′-pentylbiphenyl (5CB)and oriented by sandwiching mixtures between two pieces of rubbed glassplates. The optical absorption spectra of the oriented squaryliumdye-5CB layers exhibit high anisotropy. The third-order nonlinearoptical responses and susceptibilities χ(3)e ofsquarylium dye in 5CB are measured with light polarizations paralleland perpendicular to the orientational direction by the resonantfemtosecond degenerate four-wave mixing (DFWM) technique. Temporalprofiles of the DFWM signal of the oriented squarylium dye-5CB layerswith light polarizations parallel and perpendicular to theorientational direction are measured with a time resolution of 0.3 ps(FWHM), and are found to consist of two components, i.e., the coherentinstantaneous nonlinear response and slow response due to the formationof excited molecules. A high anisotropic ratio of χ(3)e,10.8±1.2, is observed for the oriented layers.

Asymmetric energy transfer and optical diffraction in novel molecular glass with carbazole moiety

Asymmetric energy transfer and optical diffraction under optically interfered beams was presented in composites with novel star-shaped molecular glass end-caped by carbazole moiety, α,α′,α″-tris-(4-(carbazoryl)-n-hexyloxyphenyl)-1,3,5-triisopropylbenzene (Tris). Composite consisted of Tris as host matrix, 2,4,7-trinitro-9-fluorenone (TNF) as a sensitizer, (S)-(-)-1-(4-nitrophenyl)-2-pyrrolidine-methanol (NPP) as a nonlinear optical dye and either tricresyl phosphate (TCP), n-butyl benzyl phthalate (BBP), diphenyl phthalate (DPP), or dicyclohexyl phthalate (DCP) as a plasticizer. Asymmetric two beam coupling (asymmetric energy transfer) and beam diffraction were achieved with no external field. Glass transition temperature of the composites plays an important role for these phenomena of asymmetric energy transfer and optical diffraction with no external field. Highest net gain coefficient of 59.7 cm−1 with optical gain of 151.3 cm−1 and absorption coefficient of 91.6 cm−1 was obtained for Tris/NPP/DPP/TNF (35/20/40/5) composite. TNF anion produced by laser illumination plays a key role of beam diffraction and asymmetric two beam coupling in the composites.

Permanent light-induced polar orientation via all-optical poling and photothermal cross-linking in a polymer thin film

An epoxy-based crosslinkable polymer functionalized with nonlinear optical (NLO) photochromic dye known as Red Acid Magly was polarly oriented via thermally-assisted all-optical poling to enhance the photostability of the induced order. During the writing (seeding) process the film was cross-linked by heating with a hot-plate and irradiated simultaneously by the coherent superposition of the 1.06μm fundamental and 0.532μm second harmonic beams of a nanosecond pulsed Nd:YAG laser. We demonstrate that crosslinking between the polymer matrix and the pendant chromophore groups induced during the thermally-assisted all-optical poling procedure results in a stable light-induced second order susceptibility.

Synthesis and characterization of triphenylamino-substituted chromophores for nonlinear optical applications

Two triphenylamino-substituted chromophores containing hydroxy group, which can be easily incorporated into polymer backbone or sol–gel matrix through covalent bond, were synthesized via Vilsmeier–Haack reaction and Knoevenagel condensation. These stilbene-type chromophores with different electron acceptors were characterized by elemental analysis, 1H NMR, FTIR, UV–vis spectra and thermogravimetric analysis (TGA). The hyperpolarizabilities were characterized through solvatochromic method. Compared with commercially available nonlinear optical dyes such as C.I. Disperse Red 1 (DR1), C.I. Disperse Orange 3 (DO3) and C.I. Disperse Red 19 (DR19), triphenylamino-substituted chromophores possess higher thermal stability and display better transparency in operating wavelength of electronic devices.

Ultra-fast optical switches using 1D polymeric photonic crystals

We report fabrication of ultra-fast optical switches operated at a wavelength of 1064 nm using spin-coated one-dimensional polymeric photonic crystals doped with nonlinear-optical dyes. The optical switches are controlled either by an applied electric-field voltage or by a pump light by use of two different optical-configurations. The response time of the electro-optic switch and the all-optical switch are limited by the applied voltage and the laser used, respectively. The polymeric photonic crystals can be easily fabricated with low cost.

Molecular Organization of Nonlinear Organic Films Laminated by Langmuir-Blodgett Method

In the 21st century, the optical computation is likely to be the basic technology for processing lots of information at high speed. The aim of the present research work is to develop optical logic gates or memory chips. For this purpose, we have examined the suitability of organic nonlinear optical dye material Vanadyl-phthalocyanine (VOPc). Large single crystals of this material have been fabricated by using Molecular Beam Epitaxy (MBE) technique. The epitaxial films were formed on the substrate under optimum operating conditions. However, the epitixial growth is observed only up to a limited thickness. Above this thickness, the films become non-epitaxial, which can be improved by annealing. The reformation of the epitaxial films has been confirmed. We have also reported the effects of the environment of high temperature on the multilayered tetra-tert-butyl-Vanadyl-phthalocyanine ((t-bu)4VOPc) films, formed by Langmuir-Blodgett (LB) method. The solvent used to dissolve ((t-bu)4VOPc) was 1,2-dichloroethane. The monolayer on the surface of the water was transferred to a glass substrate by the vertical dipping method. If the multilayered stack is too thick, the molecular arrangement of the film may get disturbed. The improvement in the molecular arrangement of the LB films was examined and confirmed by measuring it’s nonlinear optical susceptibility, using Maker Fringe Method. Monolayer formation on water surface depends on the surface pressure-area isotherm. If this monolayer formation is not perfect, multiplayer stacks cannot be formed. The molecular films were aligned almost perpendicular to the substrate, as estimated from the limiting molecular area of surface pressure-area isotherm. The molecular organization of the monolayer on the substrate and the molecular structure of the multilayered ((t-bu)4VOPc) films are discussed.

Near-infrared optical-absorption behavior in high-beta nonlinear optical chromophore-polymer guest-host materials. II. Dye spacer length effects in an amorphous polycarbonate copolymer host

In the second of a three-part series, spectral absorption behavior of nonlinear optical (NLO) dyes incorporated into amorphous polycarbonate, comprised of a homologous series of dialkyl spacer groups extending from the midsection of the dye molecule, is characterized by UV-Vis and photothermal deflection spectroscopy. The dyes are structural analogs of the NLO dye FTC [2-(3-cyano-4-{2-[5-(2-{4-[ethyl-(2-methoxyethyl)amino]phenyl}vinyl)-3,4-diethylthiophen-2-yl]vinyl}-5,5-dimethyl-5H-furan-2-ylidene)malononitrile]. Previous Monte Carlo calculations [B. H. Robinson and L. R. Dalton, J. Phys. Chem. A 104, 4785 (2000)] predict a strong dependence of the macroscopic nonlinear optical susceptibility on the chromophore waist: length aspect ratio in electric-field-poled films arising from interactions between chromophores. It is expected that these interactions will play a role in the absorption characteristics of unpoled films, as well. The spacer groups range in length from diethyl to dihexyl, and each dye is studied over a wide range of concentrations. Among the four dyes studied, a universal dependence of near-IR loss on inhomogeneous broadening of the dye main absorption peak is found. The inhomogeneous width and its concentration dependence are seen to vary with spacer length in a manner characteristic of the near-IR loss-concentration slope at transmission wavelengths of 1.06 and 1.3 mum, but not at 1.55 mum. The lower wavelength loss behavior is assigned to purely Gaussian broadening, and is described by classical mixing thermodynamic quantities based on the Marcus theory of inhomogeneous broadening [R. A. Marcus, J. Chem. Phys. 43, 1261 (1965)], modeled as a convolution of dye-dye dipole broadening and dye-polymer van der Waals broadening. The Gaussian dipole interactions follow a Loring dipole-broadening description [R. F. Loring, J. Phys. Chem. 94, 513 (1990)] dominated by the excited-state dipole moment, and have a correlated homogeneous broadening contribution. The long-wavelength loss behavior has a non-Gaussian dye-dye dipole contribution which follows Kador's broadening analysis [L. Kador, J. Chem. Phys. 95, 5574 (1991)], with a net broadening described by a convolution of this term with a Gaussian van der Waals interaction given by Obata et al. [M. Obata, S. Machida, and K. Horie, J. Polym. Sci. B 37, 2173 (1999)], with each term governed by the dye spacer length. A minimum in broadening and loss-concentration slope at a spacer length of four carbons per alkyl at all wavelengths has important consequences for practical waveguide devices, and is of higher aspect ratio than the spherical limit shown by Robinson and Dalton to minimize dipole interactions under a poling field.

Preparation of alumina films by the sol-gel method

This review describes our study on preparation of alumina films by a sol-gel process and their several applications that have been investigated since 1986. Alumina films were prepared from alkoxide or inorganic salt. Both as-prepared alumina films were transparent in ultraviolet, visible and near infrared regions. The alumina from inorganic salt (inorganic alumina) was structureless even after annealed at 300–700°C in air, while the alumina from alkoxide (alkoxide alumina) was in pseudo-boehmite at an annealing temperature lower than 400°C and was in γ- or δ-type at 400–700°C. Both alumina films became opaque after annealed at temperatures above 1000°C. The inorganic alumina film annealed at 800°C showed a gas permeability that was influenced by physico-chemical properties of penetrant and alumina. Composite films of alumina and poly(vinyl alcohol) (PVA) were hydrophilic but insoluble in water, and removal of PVA from the composite films by annealing at 600°C led to formation of transparent alumina films. Such properties enabled us to use a counter diffusion method for fabricating γ-Fe2O3-doped alumina films. Alumina films doped with organic dyes such as laser dyes, hole-burning dyes and non-linear optical dyes, which were fabricated by gelation of dye-added alumina sol, exhibited laser emission, hole-spectra and second- or third-harmonic generation properties, respectively. Hydrogenation of alkene was catalyzed by Ni nanoparticles doped alumina films that were prepared by gelation of Ni2+ solution-added alumina sol and annealing the Ni2+-doped alumina gel in hydrogen gas. Nonlinear optical properties were observed for alumina films doped with CdS, Au and Ag nanoparticles, which were fabricated by gelation of Cd2+, HAuCl4 and AgNO3 solution-added alumina sols and annealing the Cd2+-doped alumina gel in H2S gas and the Ag+- and Au3+-doped alumina gels in H2 gas. Rare earth metal ion-doped alumina films, which were prepared by gelation of rare earth metal ion solution-added alumina sol and annealed the ion-doped alumina gel, exhibited not only normal luminescence but also up-conversion emission, energy transfer type luminescence and long lasting luminescence.

Organic-MPS 3 nanocomposites with large second-order nonlinear optical response

Intercalated hybrid materials alternating highly nonlinear optical organic ionic dyes and inorganic MnPS 3 layers have been elaborated. We show that a spontaneous poling of the organic molecules is induced at the macroscopic scale by an ionic exchange process. In some cases, UV–visible spectroscopy evidences strong intermolecular interactions between inserted chromophores, resulting in the formation of extended J–aggregates. High nonlinear optical efficiencies are obtained in powdered samples and in nanoparticles, then confirming the interest of these structures for potential applications in photonics.

Asymmetric Two-Beam Coupling with High Optical Gain and High Beam Diffraction in External-Electric-Field-Free Polymer Composites

This paper presents high-performance asymmetric two-beam coupling, beam diffraction and holographic recording in polymeric composites without poling and applying an external electric field. The polymer composites are based on poly(2-(9-carbazoyl)ethyl methacrylate) (PCzEMA) and poly(N-vinyl carbazole) (PVCz) as host matrices with 2,4,7-trinitro-9-fluorenone (TNF) as a sensitizer, four kinds of plasticizer; tricresyl phosphate (TCP), n-butyl benzyl phthalate (BBP), diphenyl phthalate (DPP), and dicyclohexyl phthalate (DCP); and (s)-(-)-1-(4-nitrophenyl)-2-pyrrolidine-methanol (NPP) as a nonlinear optical dye. The gain coefficient and diffraction efficiency increased markedly with increasing TNF and NPP concentrations. The highest net gain coefficient of 101.9 cm-1 with optical gain of 224 cm-1 and absorption coefficient of 122.1 cm-1 was obtained for PVCz/NPP/DDP/TNF (35/20/40/5), and the highest diffraction efficiency of 88% was achieved for PCzEMA/NPP/TCP/TNF (35/30/30/5) and PVCz/NPP/DDP/TNF (35/20/39/6) composites. The BBP plasticizer significantly enhanced the speed of two-beam coupling and diffraction grating formation for both PVCz and PCzEMA composites. Holographic images stored in the polymer composites were clearly read out using a probe beam. The key point for achieving the external-electric-field-free high performance of asymmetric energy transfer and diffraction efficiency is to have a high concentration of TNF (5 or 7 wt%).

Aligned inclusion of hemicyanine dyes into silica zeolite films for second harmonic generation.

Silicalite-1 films (thickness = 400 nm) supported on both sides of glass plates (SL/G) were prepared, and hemicyanine dyes (HC-n) with different alkyl chain lengths (n, n = 3, 6, 9, 12, 15, 18, 22, and 24) were included into the silicalite-1 films by dipping SL/Gs into each methanol solution of HC-n (1 mM) for 1 d. The included numbers of HC-n per channel (N(C)) generally decreased with increasing n; that is, they were 6.4, 23.1, 15.4, 8.2, 5.7, 3.5, 0.9, and 1.2 molecules per channel, respectively. The d(33) value gradually increased with increasing n but decreased when n > 18; that is, they were 1.12, 0.50, 2.25, 3.59, 4.99, 5.30, 1.71, and 2.57 pm V(-1), respectively. However, d(33)/N(C) progressively increased with increasing n. The d(31) values were approximately 100 times smaller than the corresponding d(33) values, and the average d(33)/d(31) ratio was 109, which is higher than those of Langmuir-Blodgett (LB) films and poled polymers of nonlinear optical (NLO) dyes, by approximately 2-5 and approximately 30-50 times, respectively. The estimated average tilted angle of the dyes with respect to the channel direction was 7.7 degrees, and the calculated average order parameter was 0.97, which is approximately 480 times higher than the values observed from poled polymers. The degree of uniform alignment (DUA) generally increased with increasing n. The progressive increase of both DUA and d(33)/N(C) with n is attributed to the increase in the tendency of HC-n to enter hydrophobic silicalite-1 channels with the hydrophobic alkyl chain first. A more than 134-fold increase in DUA was observed upon increasing n from 6 to 24. The DUA of HC-24 in the silicalite-1 film reached close to 1. Although the observed d(33) values were lower than those of the LB films of NLO dyes due to very small dye densities of the silicalite films, this methodology bears a great potential to be developed into the methods for preparing practically viable NLO films.

Crosslinked Poly(amido‐amine)s as Superior Matrices for Chemical Incorporation of Highly Efficient Organic Nonlinear Optical Dyes

AbstractWe report on the synthesis and characterization of new crosslinked polymeric matrices, pertaining to the class of poly(amido‐amine)s (PAAs), functionalized with highly performing nonlinear optical (NLO) heterocycle‐based dyes as side‐chain substituents. Linear, soluble, and highly crosslinked NLO‐functionalized PAA networks can be easily prepared under mild conditions. The wide‐ranging tunability of optical and mechanical properties of these matrices makes them a superior alternative to conventional high‐Tg thermoplastic polymers.magnified image

6, 6 -distyryl-3, 3 -bipyridine derivatives: a novel class of tunable chromophores for second-and third-order nonlinear optical applications

We report on the design, synthesis, structural characterization and quadratic as well as cubic nonlinear optical (NLO) properties of a series of organic chromophores (6,6'-distyryl-3,3'-bipyridine derivatives disubstituted with donor (D) and/or acceptor (A) end-groups). The compounds are either dipolar (push–pull molecules) or apolar (symmetric D–A–A–D molecules). By lateral substitutions of the π-conjugated bridge and by varying the nature of the donor/acceptor (D/A) pair, we were able to tune both the mesogenic and NLO properties of the chromophores. Their second-order NLO properties were evaluated by the electric-field-induced second-harmonic technique. All the compounds are transparent at the second-harmonic wavelength of typical laser sources (1.32 and 1.55 μm). For the mesogenic chromophores, first hyperpolarizabilities extrapolated to infinite wavelength, β0, between 16 and 85 × 10−30 esu were measured. These compounds exhibit enhanced hyperpolarizabilities compared to typical NLO liquid crystal chromophores reported in the literature. Both the nonlinear refractive index n2 and the two-photon absorption (TPA) coefficient α2 were simultaneously measured at λ = 1064 nm, using a single-shot (50 ps, 10 Hz) multi-channel Z-scan method. For all molecular compounds, Z-scan measurements in dichloromethane solutions show a large nonlinear refractive index, close to that of pure carbon disulfide, without detectable TPA in most cases. These measurements lead to extrapolated nonresonant n2 values between 1 × 10−16 and 4 × 10−16 m2 W−1, whatever the electronic structure of the compounds. Hence, apolar symmetric D–A–A–D molecules appear to be an interesting novel family of NLO dyes.

Fast and stable photorefractive systems with compatible photoconductors and bifunctional NLO-dyes

Abstract Polymeric photoconductors carrying triphenyldiamine units and soft oligomethylene spacers were synthesized. Due to the flexible spacers, the polymers are highly soluble and could be obtained as film-forming materials with appreciably high molecular weights and low glass transition temperature ( T g ). They possess HOMO value of about −5.1 eV as determined from cyclic voltammetry. These photoconductors can be mixed with nonlinear optical dyes in any proportion to obtain stable photorefractive samples. The T g can be tuned about room temperature by just changing the composition of the guest–host photorefractive system and requires no additional amount of plasticizer. Fast photorefractive response time of about 1 ms was obtained for these new guest–host systems from degenerate four-wave mixing and two-beam coupling measurements. Further, a series of well-defined low molecular weight bifunctional compounds, TPA–Azos were synthesized in which the photoconductor moiety, triphenylamine (TPA) is covalently linked to an azo dye. The TPA–Azos exhibit T g values of 13, 36 and 42 °C and they can also be mixed with polymeric photoconductors to obtain stable photorefractive systems with low T g values. With a new setup to control and vary the sample temperature precisely, the temperature dependence of erasing dynamics of holographic gratings in these systems was studied. It reveals change of response time by three orders of magnitude over a temperature range of 13 K. The difference in behaviour of the photorefractive system above and below the T g of the sample allows us to differentiate between the time contributions due to the fast electro-optic effect and the slow orientational diffusion processes.

PHOTOSTABILITY STUDIES ON HIGH DIPOLE NONLINEAR OPTICAL ADDUCTS OF TCNQ IN POLYMER OPTICAL WAVEGUIDES

The photostabilities of nonlinear optical organic dyes doped as guests into Poly(methyl mathacrylate), (PMMA), waveguide films have been investigated using measurements of planner waveguide transmission over time. Direct photodecomposition of the dyes is observed when the doped films are exposed to wavelengths lying within the main absorption bands. The dyes exhibit a rapid photochemical degradation that is enhanced when the experiments are repeated in an air environment at the irradiation between 450 nm and 515 nm. Excitation of the zeroth-order transverse magnetic mode (TM0) by prism couplers produced complete degradation within 30 minutes. The dye photostabilities are compared to that of a commonly studied laser dye, 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran, DCM, which exhibits a photo-oxidation mechanism. The experiments in air lead to comparable degradation after 3 to 4 hours but the dye proves to be exceptionally photostable in vacuum. Further interesting results are reported on the formation of crystallites in the films when irradiated at 632.8 nm where linear absorption in the films is low. Microscopic examination of the waveguide films at the input coupling position confirms the formation of crystallites for all the films studied. Cross coupling to higher order modes from the light scattering of crystallites is revealed by scanning m-line images of the waveguides. This is associated with a marked refractive index decrease in the films. An air and humidity environment is found to favor the crystallite formation in the dye-doped waveguides.

Evidence of Spontaneous Multilayer Formation for Disperse Red-1 at a Fused-Silica/2-Propanol Interface

The film structure of a nonlinear optical azo dye (Disperse Red-1, DR-1) was probed by a combination of spectroscopic and microscopic techniques. Second harmonic generation (SHG) and linear dichroism provided evidence for the spontaneous formation of DR-1 multilayers at a 2-propanol/fused-silica interface under equilibrium conditions. Specifically, the adsorption isotherm measured by SHG exhibited two distinct adsorption regimes; the second regime (>10-3 M) being indicative of multilayer formation in which some degree of polar order was retained. The trend in apparent tilt angle measured by linear dichroism was consistent with multilayer formation at solution-phase concentrations above 10-3 M. Multilayer formation was directly observed, on a dip-coated substrate, by atomic force microscopy and further confirmed by ellipsometry. The significance of spontaneous multilayer formation with z-axis polar order in higher layers is the potential for growth of molecular multilayer systems without the need for coval...

Optical gradient materials produced via low-temperature isothermal frontal polymerization

Using a newly developed low-temperature frontal polymerization technique, poly(methyl methacrylate) (PMMA) matrices were prepared with nonuniform distributions of organic nonlinear optical dyes, with potential use as optical limiters. This technique affords lower temperature conditions than have been used before. A PMMA tube was filled with a dye, the initiator tert-butyl peroxide, and methyl methacrylate (MMA). Curing at 4°C resulted in a radial gradient of dye. An axial dye gradient was observed when MMA was overlaid and polymerization effected from a dye-doped PMMA seed using tricaprylmethyl ammonium persulfate as the initiator. In both cases, polymerization reactions were observed as a result of isothermal frontal polymerization with the subsequent formation of a nonlinear concentration distribution of the optical dye dopants. Low temperatures are desirable to eliminate thermal and photothermal degradation of temperature-sensitive dyes during the polymerization. The preparation of long polymer rods with organic dye gradients on the scale of several centimeters can also be realized with the use of low-temperature polymerization and the gradients controlled by the concentration of initiator. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 686–691, 2001

Orientation of Nonlinear Optical Active Dyes in Electrostatically Self-Assembled Polymer Films Containing Cyclodextrins

Orientation of Nonlinear Optical Active Dyes in Electrostatically Self-Assembled Polymer Films Containing Cyclodextrins

Femtosecond fluorescence dynamics and molecular interactions in a water-soluble nonlinear optical polymeric dye

The excited state dynamics of a water-soluble polymeric dye poly(S-119) was investigated using femtosecond time-resolved fluorescence upconversion. Multi-exponential relaxation of fluorescence was observed for poly(S-119) in picosecond and sub-picosecond time ranges. The azo-chromophore of the functionalized polymeric dye Sunset Yellow was used as a model compound for detailed investigations of intermolecular interactions. Excited state decay of this azo-dye can be described by a two-exponential decay law with time-constants of ∼0.48 ps and 1 ps. Fluorescence anisotropy decay was investigated for both systems. The difference in excited state dynamics between the polymeric dye and the azo-chromophore is explained in terms of inter-molecular interactions resulting in intra-chain aggregate formation.

New crosslinked polymer systems with high and stable optical nonlinearity

Thermo-crosslinkable copolymers (PGMAA and PGMAS) of glycidyl methacrylate containing azobenzene chromophores (20 mol%) and stilbene chromophores (19 mol%) respectively were synthesized and characterized. In order to obtain crosslinked polymers with high and stable second-order nonlinear optical (NLO) property, PGMAA and PGMAS were doped with a reactive nonlinear optical (NLO) dye, 4-nitro-4′-aminobiphenyl (20 mol% of the glydidyl group). In the poled state, these doped polymers systems (PGMAD and PGMSD) can be thermo-crosslinked to yield materials with high second-order (NLO) coefficient ( d 33) of 4.33×10 −7 esu and 4.74×10 −7 esu respectively. The investigation of SHG decay at room temperature and 100°C showed that the polymer networks much improved the SHG stability.