We report here the preparation of highly homogeneous multifunctional fullerene thin films for photonics using the electrostatic self-assembled monolayer technique at room temperature for the first time. The monolayers and multilayers were characterized via contact angle measurements, UV-vis spectroscopy and atomic force microscopy. These results demonstrated that close-packed, highly uniform fullerene or fullerene/metal cluster films with micron-thickness could be formed on various substrates including silicon, glass, metal and plastics.

J-aggregates of squarylium dyes in Langmuir films have been found to exhibit highly efficient and ultrafast nonlinear optical properties. We established a novel method for making Langmuir- Blodgett (LB) films of J-aggregates with a single absorption band at 784 nm. Deposition of the LB-films was carried out under excess compression of the Langmuir films at a constant speed. Coating the surface of the LB-film with a glassy poly-perfluorocarbon was found to enhance and stabilize the formation of J-aggregates. Characterization of morphology using a near-field scanning optical microscope (NSOM) showed that this LB-film has a highly ordered structure comprising 2- dimensional domains of J-aggregates. We also observed nonlinear-optical responses from this LBfilm. Ultrafast decay of absorption change (250 fs) with quite low saturation energy (3.4 μJ/cm2•pulse) was observed in femtosecond pump-probe measurements. These results suggest highly delocalization of excited states in the J-aggregates of this LB-film with the 2-dimensional mono-molecular layer structure which initially formed in the Langmuir film.

We study second-order nonlinear optical properties of enantiomerically pure and racemic Langmuir-Blodgett films of a chiral helicenebisquinone. Supramolecular aggregation of the material enhances the nonlinear efficiency of the enantiomerically pure material. We also show that the material is potentially useful for constructing quasi-phase-matched structures for frequency conversion.

We report the synthesis and sol-gel polymerization of 4-nitro-N,N-bis[(3- triethoxysilyl)propyl]aniline 1. An efficient synthesis of the monomer was developed by the hydrosilylation of N, N-diallyl-4-nitroaniline. Optical quality thin films were synthesized by spin coating an n-butanol solution of 1 using formic acid as catalyst and source of water. We improved the temporal stability of the NLO signal from films prepared from 4-nitro-N,N-bis[(3-triethoxysilyl)propyl]aniline by increasing the intensity of the poling field and extending the heating period during the poling/curing stage. By Maker fringe analysis, a X(2) value of 9 × 10−8 esu was measured for these polysilsesquioxanes. If one assumes that the major component of the NLO effect is along the z-axis, the X(2) value corresponds to a d33 coefficient of 18.9 pm/V and a r33 value of 4.7 pm/V.

A new method for the build-up of non-centrosymmetric multilayer thin films has been developed for the first time using an electric field-assisted electrostatic self-assembled monolayer (EF-ESAM) technique. An increase by 116% of the second-harmonic intensity of the films has been observed in comparison with that of ESAM film.

The formation of acentric films using alternating polyelectrolyte deposition (APD) has been achieved on hydrophobic and hydrophilic glass substrates. APD is a layer-by-layer technique for the formation of polymer films by alternately immersing a substrate in aqueous solutions of a polyanion and a polycation. APD provides precise control of the overall film thickness that through automated processing may exceed a thousand layers. In this study, APD films were made of an NLO-active polycation, stilbazolium-substituted polyepichlorohydrin (SPECH), and NLO-inactive polyanions. The peak maximum UV-Visible absorbance in transmission through the films was linear as a function of the number of bilayers. Second harmonic generation (SHG) was used as a tool to indicate acentric order of polarizable sidechain chromophores within the APD films. The SHG exhibited the expected quadratic intensity increase with film thickness.

Tuning the degree of bond-length alternation in organic nonlinear optical materials is a powerful paradigm for the design of organic materials with large molecular hyperpolarizabilities (β). Several research groups have employed this paradigm in the design and synthesis of NLO materials incorporating donor-acceptor polyenes. Increased bond-length alternation in polyenes leads to decreased barriers to rotation about C=C bonds and, hence, increased conformational flexibility. Since the degree of bond-length alternation is solvent dependent, so is the degree of conformational flexibility. In an effort to probe the influence of conformational flexibility on NLO response, we synthesized a series of simple donor-acceptor polyenes that are either conformationally flexible (la, 2a, 3a) or rigid (1b, 2b, 3b). For each pair of molecules ZINDO sum-over-states calculations predict a larger value of βμ, for the conformationally flexible isomer, but EFISH measurements (CHCl3) display mixed results. Various explanations for this behavior will be considered.

We have developed a single-mode optical waveguide utilizing siloxane polymer on ceramic substrate for opto-electronic multichip modules (O/E-MCM) to operate Tera bps. In this paper, we describe group velocity dispersion for the optical waveguide utilizing siloxane polymer on ceramic substrate. The group velocity dispersion becomes 0 fs/cm·nm at around 1310 nm and 1530 nm wavelength. There is abnormal dispersion at around 1530 nm. The results showed that the group velocity dispersion of the optical waveguide was significantly related to the absorption spectrum of siloxane polymer. The group velocity dispersion of the optical waveguide is about 0.4 fs/cm·nm at 1550 nm wavelength. When a 500 femto seconds optical pulse, which has 16 nm for spectrum width, pass through the 50 mm long optical waveguide, pulse expansion is estimated 20 fs/cm·nm. This expansion of spectrum is well to distinguish femto seconds optical signals. Thus, the optical waveguide utilizing siloxane polymer is capable for femto seconds optical pulses transmission.

To understand the properties of light-sensitive compounds used in optical limiters having photoinduced charge transfer mechanisms, we have investigated the photophysics of a series of di(2-thienyl-3,3'-butyl)polyenes. Spectroscopic measurements, including UV/Vis, fluorescence, fluorescence lifetimes, fluorescence quantum yields, triplet state lifetime, solvent effects and two-photon absorption coefficient were obtained as a function of the number of double bonds(n = 1-5). Trends in the data reflected the ordering, energy gap between and mixing of 1Bu* and 1Ag* excited state configurations.

New combined main- and side-chain azobenzene polyesters, which exhibit an intensity dependent refractive index, have been prepared in order to optically fabricate nonlinear waveguides. Novel sulfone azobenzenes, a diester, (4-[[5-(ethoxycarbonyl)pentyl]sulfonyl]-4'-[[5-(ethoxycarbonyl)pentyl]methylamino] azobenzene, and a diol, 4-[[(8-hydroxy-7-methylhydroxy)-octyl]sulfonyl]-4'-N, N-dimethylamino azobenzene, have been used to prepare new polyesters by transesterification in the molten state. The polyesters have been characterized by UV-visible spectroscopy, differential scanning calorimetry (DSC), size exclusion chromatography (SEC), third harmonic generation (THG) and optical anisotropy measurements. The molar masses of the polyesters were in the range of 5000-10000 g mol−1, which was sufficient in order to spin coat thin films. From THG measurements the polymers are shown to possess an offresonance electronic X(3) of the order 10−12 esu corresponding to a nonlinear refractive index of 2.3×10−14 cm2/W.

Model dendrimers based on bis-(diphenylamino)stilbene repeat units have been synthesized and shown to have very stable bipolaronic charge states. Calculations at the AM-1 level predict two orders magnitude enhancement in the third-order nonlinearity in going from the neutral to bipolaron state. Measurement of two-photon cross-sections for PPV dimers with attached diphenylamino donor groups show enhanced two-photon cross-sections for ns pulses. Preliminary evaluation of one of the model dendrimers indicates even larger two-photon cross-sections are possible.

Bis-(dialkylamino) and bis-(diphenylamino) substituted diphenylpolyenes have recently been shown to have exceptionally large two-photon cross-sections, and have also been used in optical power limiting (OPL) applications. Another potential mechanism for OPL in these materials involves the photogeneration of highly absorbing polaronic radical-cations or bipolaronic dications which can then function as highly absorbing reverse saturable absorbers (RSAs). The synthesis of series of these unique polyenes has been carried out, as well as studies of chemically induced bipolaron formation in solution. In order to actually be used in OPL devices, it is probable that these chromophores will need to be incorporated into polymer formulations, In this paper we describe three distinct ways that these chromophores can be incorporated in polymer structures: (1) as pendant groups attached to a PMMA backbone, (2) as formal repeat units in a copolymer, and (3) perhaps the most interesting, as surface attached functionalities in dendrimer formulations. The formation of bipolaron charge species in these polymers will be addressed.

Previous studies of the second and third order nonlinear optical properties of organic molecules have shown enhancement of the nonlinear response when second row elements replace first row elements (e. g. S for O) in electron donating groups. Various substituted amino functionalities have been utilized extensively as strong donors in the design of molecules for both second and third order NLO applications. However, to date, no research groups have reported a systematic study of the effect of replacing N (nitrogen) by P (phosphorus) in various chromophore functionalities. We have now synthesized a series of bis(diphenylphosphio)diphenylpolyenes with up to five double bonds, a bis-(diphenylphosphino)-PPV dimer, and a diphenylphosphino DANS equivalent. The absorption characteristics compared to the N equivalents, and the implications for photonics applications will be discussed.

The optical limiting performances of donor-buckminsterfullerene (C60) dyads have hitherto been unreported. The predicted large excited state absorption cross-section of such dyads in their charge-separated states would enable them to exhibit enhanced optical limiting relative to their individual components. We report herein the synthesis and optical limiting characterization of a novel porphyrin-buckminsterfullerene dyad, in which the porphyrin and C60 moieties are held within close proximity of one another by an o-phenylene bridge. The porphyrin-C60 dyad was synthesized via 1,3-dipolar azomethine ylide cycloaddition, and was obtained in 37.0% yield. Optical limiting measurements at 532 nm using 3-ns pulses show that the limiting performance of the dyad is poorer compared to its model compounds. Possible reasons for the worsened performance of the dyad will be discussed.

The interaction of weak electrical field with the molecular dipole of the MBA-NP crystals is investigated. Such interaction affects the misorientation and size of the perfect diffracting regions of the crystal, which is monitored by mapping the Bragg-surface diffraction condition. This diffraction technique has also confirmed that the diffracting regions are large enough to allow primary extinction and the non-uniform mosaicity along the crystal surface.

We report here our preliminary results on the synthesis and characterization of a new family of metal-containing polymers incorporating 8-hydroxyquinoline. These polymers have the following structural features: a metal center, a chromophore, and a flexible spacer group with variable length. These structural features allow us to have an appreciable degree of control over various physical properties of these materials. We report on three different types of polymers: polyethers, polyesters, and polyamides. The chromophores in these polymers were incorporated in the backbone and in one case as a side chain of polyesters.

J aggregates cyanine dyes have been successfully doped directly in sol-gel derived silicate thin films. The films are transparent, homogeneous and stable at room temperature. The J aggregates successfully incorporated in rigid SiO2 framework were characterized by absorption spectroscopy and fluorescence microscopy. The films are expected to be useful for non-linear optical devices, multiple photon recording and photoelectric cell.

Ultrafast optical responses of the organic films containing squaryliurn dye J-aggregates prepared by simple spincoating method were investigated. Some SQ films exhibited a sharp absorption peak originated from J-aggregates and especially the SQ derivative which has dibutylamino bases at the end of benzene rings forms good J-aggregates in the films without any extra treatment. Time-resolved difference absorption spectra were measured about the SQ44 film. Clear bleached absorption peak and its fast recovery were observed. The decay time was determined to be about 220 fs at 50 MW/cm2 excitation intensity. Sample preparations and all the measurements were performed in air at room temperature.

The electrostatic self-assembly of multilayer thin films by alternate adsorption from polyelectrolyte solutions spontaneously leads to the formation of noncentrosymmetric structures if the molecules themselves have net dipole moments. Significant second-order nonlinear optical susceptibility has been observed in such films, using both commercially available chromophores and molecules specifically designed to yield an enhanced net dipole moment. Recent results indicate the capability to fabricate piezoelectric films using the same method. The nature of the deposition process results in an alignment of the chromophores that is stable over time and to temperatures up to 150°C, in contrast with poled polymers. ESA films offer the additional major advantages of excellent homogeneity and low optical loss, high thermal and chemical stability, and low cost.

Organic chromophores have been exploited for a wide range of discrete optical and electronic functions as well as a growing number of combined opto-electronic functions. We are pursuing development of organic and polymer materials for a range of applications that require properties including liquid crystallinity, second order optical nonlinearity, photorefractivity and, more recently, special nonlinear optical behavior involving molecular chirality.