New all-optical poling (AOP) experiments conducted in multi-core dye-doped poly(methyl methacrylate) optical fibers show that self-sustained and faster rise time second harmonic generation is possible in polymers.

Self-sustained all-optical poling second-harmonic generation (SHG) experiments are conducted in single-core and multicore dye-doped poly(methyl methacrylate) optical fibers. By tuning the polarization of the fundamental beam, the SHG signal is degraded and is reconstructed spontaneously up to its initial level. We found a new situation in which the photo-induced self-organization of azo polymers creates a well-ordered periodic structure.

A phenylacetylene macrocycle (PAM) derivative containing triphenylamine as the framework was synthesized in one-step Sonogashira coupling. The photophysical and electrochemical properties were investigated in details. This hexamer shows significant enhancement in two-photon absorption cross-section relative to reported PAM derivatives.

We review experimental studies of nonlinear optics in large-core dye doped plastic optical fibres. In particular second-order nonlinearity in all-optical poled optical fiber is promising for application to electro-optic switching, second-harmonic generation, and frequency conversion.

Three pyridylphosphonic acids, 3-pyridylphosphonic acid 1, 5-(dihydroxyphosphoryl)nicotinic acid 2, and 3,5-pyridinediyldiphosphonic acid 3, were synthesized and structurally investigated by solid state FT-IR and single crystal X-ray diffraction methods. All compounds appear in zwitterionic forms in the solid state with a proton transferred from the phosphonic group toward the pyridine N-atom. Strong hydrogen-bond interactions O-H center dot center dot center dot O and N-H center dot center dot center dot O organize the molecules of the compounds into polar three-dimensional networks. The crystal structures are additionally stabilized via weaker C-H center dot center dot center dot O hydrogen bonds and pi center dot center dot center dot pi or C=O center dot center dot center dot pi interactions. Powder second harmonic generation and solution NMR spectra were measured as well. The NMR spectra revealed that the double bonds of the functional groups (P=O and C=O), although differently oriented versus the N-py atom, are coplanar with the aromatic rings in all stable, low energy conformers of compounds 1-3 in solution. In crystals, however, the P=O bonds are tilted toward the ring by 10.77(7)degrees in 1, 70.42(8)degrees in 2 and by 43.97(7)degrees and 6.56(8)degrees in 3. All three compounds exhibit moderate powder SHG efficiencies compared to that of urea.

We present experimental studies of all-optical poling (AOP) in large-core dye-doped poly(methyl methacrylate) plastic optical fibers. We show that the confinement of light within the fiber core permits us to reach the upper limit of second harmonic generation achievable by AOP using repeated trans-cis isomerization. Quantification of the output power indicates self-seeding that can counteract relaxation of the orientation during readout of the induced nonlinearity.

We describe a series of nine new complex salts in which electron-rich Ru-II or Fe-II centers are connected via pi-conjugated bridges to six electron-accepting N-methyl-/N-arylpyridinium groups. This work builds upon our previous preliminary studies (Coe, B. J. J. Am. Chem. Soc. 2005, 127, 13399-13410; J. Phys. Chem. A 2007, 111, 472-478), with the aims of achieving greatly enhanced NLO properties and also combining large quadratic and cubic effects in potentially redox-switchable molecules. Characterization has involved various techniques, including electronic absorption spectroscopy and cyclic voltammetry. The complexes display intense, visible d -> pi* metal-to-ligand charge-transfer (MLCT) bands, and their pi ->pi* intraligand charge-transfer (ILCT) absorptions in the near-UV region show molar extinction coefficients as high as ca. 3.5 x 10(5) M-1 cm(-1). Molecular quadratic nonlinear optical (NLO) responses beta have been determined by using hyper-Rayleigh scattering at 800 and 1064 nm and also via Stark (electroabsorption) spectroscopic studies. The directly and indirectly derived beta values are very large, with the Stark-based static first hyperpolarizabilities beta(0) reaching as high as ca. 10(-27) esu, and generally increase on extending the pi-conjugation and enhancing the electron-accepting strength of the ligands. Cubic NLO properties have also been measured by using the Z-scan technique, revealing relatively high two-photon absorption cross sections of up to 2500 GM at 750 nm.

Polyhedral oligomeric silsesquioxane (POSS) cages containing an iminofullerene species are reported herein. Monosubstituted benzyl chloride POSS was synthesized, and subsequently reacted with sodium azide to form mono benzyl azide POSS. The azide was subsequently reacted with C 60 in anhydrous, degassed toluene to yield the desired POSS iminofullerene compound. The prepared compounds were characterized by multinuclear NMR, electrospray mass spectrometry, elemental analysis, UV–vis, fluorescence and optical power limiting measurements. Copyright © 2009 John Wiley & Sons, Ltd.

The first reported examples of polyhedral oligomeric silsesquioxane (POSS) cages containing a fulleropyrrolidine species are reported herein. Monosubstituted POSS-dioxalane species were synthesized through the hydrosilylation of a silyl-dioxalane with mono-vinyl substituted POSS. Subsequent deprotection yielded the desired aldehyde functionality. An alternative synthetic pathway, involving the nucleophilic substitution of mono-benzyl chloride POSS with 4-hydroxybenzaldehyde yielded the desired aldehyde functionality. Each mono-aldehyde POSS was then reacted with N-methylglycine and C60 to yield the desired POSS fulleropyrrolidines. The prepared compounds were characterized by multinuclear NMR, electrospray mass spectrometry, elemental analysis, UV–vis, fluorescence and optical power limiting measurements. Copyright © 2008 John Wiley & Sons, Ltd.

Triphenylamine derivatives bridged by methylene units afford a near planar molecular platform in a series of one dimer and two oligomers exhibiting increased structural rigidity compared to that of their parent triphenylamines. This series of dendrimers show significantly enhanced two-photon absorptions that are up to 3-fold that of triphenylamines with similar molecular size and structure.

We have studied dispersion of the cubic nonlinear optical properties of organic and organometallic nonlinear absorbers. The results indicate that a multitude of excited states may be contributing to the resonances seen in the real and imaginary part of the complex hyperpolarizability. Attempts to understand the relation between the real and imaginary part of the hyperpolarizability in terms of a Kramers-Kronig transform are undertaken.

There is much interest in nonlinear absorbing chromophores for applications in photonics, nanophotonics and biophotonics. We have performed studies of dispersion of the nonlinear absorption cross sections and the refractive nonlinearities of organic and organometallic nonlinear chromophores using the technique of Z-scan, with a tunable amplified femtosecond laser system. Z-scan is less sensitive than the popular technique of two-photon induced fluorescence but has advantages of being suitable for non-fluorescent substances and providing information on both absorptive and refractive nonlinearities. We have analysed the experimental results in terms of simple models and using the Kramers-Kronig transformation as shown in this paper for Coumarine 307 and an organometallic dendrimer. The dispersion curves are often dominated by two-photon resonances but inclusion of other nonlinear mechanisms seems to be necessary for better understanding of their features.

The first reported examples of polyhedral oligomeric silsesquioxane (POSS) cages containing a fulleropyrrolidine species are reported herein. Monosubstituted POSS-dioxalane species were synthesized through the hydrosilylation of a silyldioxalane with mono-vinyl substituted POSS. Subsequent deprotection yielded the desired aldehyde functionality. An alternative synthetic pathway, involving the nucleophilic substitution of mono-benzyl chloride POSS with 4-hydroxybenzaldehyde yielded the desired aldehyde functionality. Each mono-aldehyde POSS was then reacted with N-methylglycine and C60 to yield the desired POSS fulleropyrrolidines. The prepared compounds were characterized by multinuclear NMR, electrospray mass spectrometry, UV-VIS, fluorescence and optical power limiting measurements.

The optical second-harmonic generation (SHG) and the linear optical properties were investigated in a planar cell containing aligned nonchiral nematic derivative of B10H102−: 1-(4-heptyloxypyridin-1-yl)-10-(4-pentyl-1-thiacyclohexyl)-closo-decaborane (HPTD) as a function of temperature. The compound showed a low level of the SHG signal in the polycrystalline state, and no nonlinear optical effect was detected in the fluid nematic state (N) either in the presence or absence of an orienting electric field. When frozen, the resulting thermodynamically unstable nematic glassy phase (glassy N) unexpectedly exhibited the second-order nonlinear optical properties, implying a partial polar order in the arrangement of the in-plane-aligned molecules in a liquid-crystal cell. The efficiency of the SHG was analyzed for two polarization configurations yielding the main component of the second-order nonlinear susceptibility χxxx(2)=2.3±0.3pmV−1 along the nematic director x. A comparison of the experimental susceptibility with a hypothetical one estimated from the vectorial component of the molecular hyperpolarizability showed a relatively low degree of the spontaneous polar order. The dispersion of the principal refractive indices in the glassy state of HPTD was derived from dichroic absorption spectra using an interference fringe method and fitted with a Sellmeier-type equation. At 527nm the birefringence of HPTD is Δn=0.31.

Disperse Red 1 (DR1) doped TiO2-SiO2 inorganic-organic hybrid polymers were prepared by an anhydrous sol-gel process and second harmonic generation (SHG) of the fundamental 1053nm in these polymeric thin films was measured using Maker-fringe method. The nonlinear optical activity of DR1 in the thin films was studied by corona poling at different temperature (from room temperature to 140°C), and the stability of SHG after switching off corona power was evaluated by analyzing the SHG decay dynamics. Experimental results showed that the stability of the SHG of DR1 significantly increases with the cross-linkage degree of the TiO 2 SiO 2 hybrid polymer network, and that the second harmonic coefficient d 33 increases as the DR1 concentration increases. TiO 2 -doping can promote the polymerization of unsaturated C=C double bonds in the hybrid thin films during in-situ hot poling, enhancing the cross-linkage of the network of the hybrid material, and resulting in a great improvement of the stability of SHG. The excellent stability of second harmonic generation in the hybrid polymer thin films suggests that TiO 2 -doped inorganic-organic hybrid polymer is promising for chromophore doping for nonlinear optical applications.

Third-order nonlinear optical properties were investigated for the system incorporating the Disperse Red 1 dye and the deoxyribonucleic acid - cetyltrimethylammonium complex (DNA-CTMA). The interaction of the dye with the DNA chains does not lead to major changes of the nonlinear optical effects due to the DR1 dye. Polarization dependences of the nonlinear absorption in this system reveal, however, some indications that the interactions may lead to ordering of the dye molecules against the DNA chains.

DNA is a polyelectrolyte capable of forming thin films with interesting optical properties. We investigated refractive indices and optical anisotropy of films of the native, sodium ion-based DNA (Na-DNA) and DNA bearing the cetyltrimethylammonium ion (DNA-CTMA) using a prism coupler technique. The light polarization direction was either parallel (n(TE)) or perpendicular to the surface plane of the films (n(TM)). The index values and the birefringence of DNA films vary considerably depending on the type of the counter-ion, the film fabrication method and the relative humidity (RH) of the environment. A high negative birefringence in films of Na-DNA, n(TE)-n(TM) = -0.03 at an RH similar to 55 %, was measured in solution-cast films, indicating that the optically anisotropic DNA molecules are aligned in the plane parallel to the film surface. Refractive indices of DNA-CTMA thin films were smaller and more isotropic than those for films of Na-DNA polymer. The prism coupler reflectance curves showed a hysteresis of the index values when the RH of a DNA-CTMA film environment varied. Polarization microscopy studies showed liquid-crystalline textures at the edges of Na-DNA and DNA-CTMA films.

Highly oxygen-rich SiOx thin films were prepared using a helicon plasma activated reactive evaporation technique. A small second-order optical nonlinearity was observed in the as-grown films, and thermal poling induced nonlinearity in the films was found to be much larger than that in stoichiometric SiO2 films. These phenomena were associated with the non-impurity defects in the oxygen-rich films.