J. Luc

Nonlinear optics and surface relief gratings in alkynyl–ruthenium complexes

Generally, the organometallic complexes rich in carbon and containing π-conjugated chains are materials interesting for the study of electronic transfer processes. Currently, the ruthenium–acetylide organometallic complexes form part of the most studied organometallic compounds in nonlinear optics. In this work, we highlight the nonlinear optical properties and the photo-induced structure of new organometallic complexes containing a ruthenium–acetylide donor fragment able to compete with the strongest organic donors. We determine, using various experimental techniques (degenerate four-wave mixing, second and third harmonic generation), the influence of the functionalization of these molecular structures on the improvement of their second-and third-order nonlinear optical properties exploiting in particular the nature of the acceptor fragment and the π-conjugated transmitter. Also we present the dynamics of formation of photo-induced surface relief gratings using a transmission holographic technique and the atomic force microscopy on ruthenium–acetylide complexes containing an azobenzene fragment.

Comparison of Z-scan and THG derived nonlinear index of refraction in selected organic solvents

Nonlinear index of refraction of a series of organic solvents, measured by the nonlinear imaging (z-scan) technique, is compared with the same values derived from optical third-harmonic generation (THG). The systematic differences in the values obtained from the z-scan measurements and from THG are attributed to three factors: the value of the standard used in THG measurements, important rotational contribution in z-scan measurements, and the difference in dispersion for n2 derived from Kerr susceptibility and those derived from THG measurements. Using the recently proposed standard silica susceptibility value, one obtains a very good agreement for silica and significant differences for the solvents, particularly for CS2 and chlorobenzene. A correction based on a three-level model for centrosymmetric media is applied for dispersion.

Design and photoinduced surface relief grating formation of photoresponsive azobenzene based molecular materials with ruthenium acetylides

Novel photoresponsive materials based on ruthenium(II) σ-acetylides coupled to an azobenzene moiety in the main π-conjugated chain have been synthesized. The introduction of a metal acetylide fragment in the same conjugated chain as the azobenzene induces the trans-cis-trans isomerization of the azo unit, while the rate of the thermal cis → trans back isomerization increases with increasing overall electron richness of these compounds. These azobenzene-containing ruthenium(II) acetylides show satisfactory processability and give rise to spin-coated uniform thin films. Formation of surface-relief gratings on their amorphous thin films and in a PMMA polymer matrix using a picosecond pulsed laser at 532 nm results in instantaneous inscription: saturation of the first order diffraction efficiency and of the modulation amplitude of gratings were obtained in less than 1 s, while the orientation of these azodyes remains unchanged for up to 6 months.

Type structure, which is composed of organic diammonium, triiodide and hexaiodobismuthate, varies according to different structures of incorporated cations

Type structure of (H3N–R–NH3)2I3BiI6, which consists of sheets of organic entities together with triiodide anions separated by layers of BiI6 octahedra, is defined by triiodide, hexaiodobismuthate, and organic diammonium. The prototype structure of (H3N(CH2)2SS(CH2)2NH3)2I3BiI6 (1) can accommodate various changes according to the nature of the organic group, such as conformation, length or size. In (H3N(CH2)2SS(CH2)2NH3)2I3BiI6·0.5H2O (2), acentric symmetry resulted from the lattice water molecules render the SHG property. Whereas in (H3N(CH2)4NH3)2(I3)0.5(I(H2O)2)0.5 BiI6 (3), water molecules are incorporated in the main framework by substituting two iodine atoms of I3− anion, in the structure of (H3NCH2(C6H10)CO2H)4(I3)2BiI6 H3O (4), pairs of linear triiodide entities [I3⋯I3]2− (d(I3−⋯I3−) = 3.77(1) A) are observed, owing to the super-long diammonium cations of two trans-4-methylammonium cyclohexane carboxylic acid linked together via hydrogen bonding between carboxylate groups.

Study of surface relief gratings on azo organometallic films in picosecond regime.

Materials for optical data storage and optical information processing must exhibit good holographic properties. Many materials for these applications have been already proposed. Here we describe a grating inscription process characterized by short inscription time and long-time stability. A series of ruthenium-acetylide organometallic complexes containing an azobenzene fragment were synthesized. Photo-induced gratings were produced by short pulse (16 ps, 532 nm) laser irradiation. The surface relief gratings formed at the same time were observed by atomic force microscope. In this work, we highlight the short inscription times brought into play as well as the good temporal stability of these gratings stored at room temperature. We study the influence of the polarization states and the light intensity of writing beams on the dynamics of the surface relief gratings formation and we compare these results with those of a known representative of azobenzene derivative (Disperse Red 1). Lastly, we show that it is possible to write two-dimensional surface relief gratings.

Study of Nonlinear Optical and Structural Properties of Organometallic Complexes

In the frame of this work, we studied organometallic complexes in form of thin films oriented by corona poling. We report measurements of second and third-order nonlinear optical properties (NLO) obtained by SHG and THG techniques. For each compound studied, we determine the electronic contribution of the effective second and third-order nonlinear susceptibilities. Finally, we use X-ray diffraction to study structure of these compounds, induced by corona poling.

Polymorphism of lead(II) benzenethiolate: a noncentrosymmetric new allotropic form of Pb(SPh)2

Depending upon its conditions of crystallization, lead(II) benzenethiolate can exist in two forms: a low-temperature centrosymmetric phase α-Pb(SPh)2 which can be converted by heating into the noncentrosymmetric, 2nd order NLO strongly active and room temperature metastable β-Pb(SPh)2 phase, thus affording an example of transition towards noncentrosymmetry induced by a rise of temperature.

Some selected and functionalised organometallic molecules for NLO applications

Organometallics nano complexes are important targets for the construction of advanced materials, the investigation of electron-transfer processes and of novel devices for non-linear optical (NLO) applications. In this work the diagnostic and characterisation of novel molecular organics nano complexes thin films functionalized for NLO applications will be discussed. On other hand a rich study of the formation of surface-relief gratings (SRGs), using a picosecond pulsed laser at 532 nm, resulted in instantaneous inscription will be presented.

Calibration and rotational contribution in third-order NLO properties characterization

Nonlinear index of refraction n2 of a series of organic solvents was measured by the nonlinear imaging (z-scan) technique. The results were compared with the values derived from the optical third harmonic generation (THG) done at the same (1064.2 nm) wavelength. The systematic differences between the values obtained from the z-scan measurements and from THG are attributed to mainly two factors: rotational contribution to n2 in z-scan measurements, where one measures the light induced birefringence and to the difference in dispersion for n2 derived from Kerr susceptibilities with respect to those derived from THG measurements. The difference is discussed in terms of a three level model for centrosymmetric structures. Applied to silica and benzene the model shows, at the measurements wavelength, a small difference between the two determinations in the case of silica and quite an important one in the case of benzene. A good agreement is observed for silica with the recently determined THG value.

Alkynyl-ruthenium complexes for nonlinear optical applications

Currently, the ruthenium-acetylide organometallic complexes form part of the most studied organometallic compounds in nonlinear optics. We highlight the nonlinear optical properties and the photo-induced structuration of new organometallic complexes containing a ruthenium-acetylide donor fragment able to compete with the strongest organic donors. The experimental studies of third-order nonlinear optical properties of alkynyl-ruthenium complexes are presented. Also we present the dynamics of formation of photo-induced surface relief gratings using a transmission holographic technique and the atomic force microscopy on ruthenium-acetylide complexes containing an azobenzene fragment.