Characterisation of a new sol-gel precursor for a SiO<Subscript>2</Subscript>-rhodamine 6G hybrid class II material

The entrapment of organic dyes in inorganic solids offers several advantage for solid-state laser applications with respect to the use of liquid or polymer hosts. Among the various inorganic hosts, silica is preferred for its superior mechanical, thermal and optical properties. Organic dyes, such as Rhodamine 6G (Rh6G), can be immobilised in SiO₂ both physically (materials of class I), and by covalent bonds (class II materials). In the past years Rh6G-SiO₂ class I hybrids were prepared. In this work we propose, for the first time, a Rh6G-SiO₂ class II hybrids. We describe the preparation of a suitable sol-gel Rh6G precursor verified by FT-IR analysis and report the characterization of the hybrid materials by means of thermal and porosimetric analysis and optical spectroscopy measurements. The precursor is thermally stable up to ∼250°C, and its optical characteristics (UV-VIS absorbance and photoluminescence, PL) do not change with respect to those of the pristine dye molecule. The PL spectra of the final hybrids show that they are promising candidates for applications in solid state dye lasers.     

Click assembly of dye-functionalized octasilsesquioxanes for highly efficient and photostable photonic systems

New hybrid organic–inorganic dyes based on an azide‐functionalized cubic octasilsesquioxane (POSS) as the inorganic part and a 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BDP) chromophore as the organic component have been synthesized by copper(I)‐catalyzed 1,3‐dipolar cycloaddition of azides to alkynes. We have studied the effects of the linkage group of BDP to the POSS unit and the degree of functionalization of this inorganic core on the ensuing optical properties by comparison with model dyes. The high fluorescence of the BDP dye is preserved in spite of the linked chain at its meso position, even after attaching one BDP moiety to the POSS core. The laser action of the new dyes has been analyzed under transversal pumping at 532 nm in both the liquid phase and when incorporated into solid polymeric matrices. The monosubstituted new hybrid dye exhibits high lasing efficiency of up to 56 % with high photostability, with its laser output remaining at the initial value after 4×10⁵ pump pulses in the same position of the sample at a repetition rate of 30 Hz. However, functionalization of the POSS core with eight fluorophores leads to dye aggregation, as quantum mechanical simulation has revealed, worsening the optical properties and extinguishing the laser action. The new hybrid systems based on dye‐linked POSS nanoparticles open up the possibility of using these new photonic materials as alternative sources for optoelectronic devices, competing with dendronized or grafted polymers.     

Efficient Nonlinear Optical Properties of Dyes Confined in Interlayer Nanospaces of Clay Minerals

Nonlinear optical (NLO) responses from organic dyes can be maximized when the dyes are aligned in appropriate manners in bulk materials. The use of restricted nanospaces provided by interlayer spacing of inorganic layered materials is a promising strategy for imposing suitable molecular alignments for NLO materials on dyes. The hybrid materials thus obtained exhibit salient NLO responses owing to the improved molecular orientation. In some cases, extension of the π‐electron system as a consequence of improved molecular planarity, obtained by the intercalation of a dye into the 2‐dimensional interlayer space of an inorganic layered material, is also observed as a factor that enhances NLO responses of chromophores at the molecular level. This review focuses on recent progress in the strategies for controlling the molecular orientation of NLO‐phores by employing clay minerals, which are one of the typical inorganic layered materials. In addition, development of a means for fabricating composites that satisfy the properties of an optical material, such as a sufficient size and thickness, a flat surface, and low light‐scattering characteristics is required to utilize the superior NLO properties observed for clay/dye hybrid materials for practical applications. A novel means for obtaining such a hybrid material is also outlined.     

Photochromic Doped Sol-Gel Materials for Fiber-Optic Devices

Photochromic-doped sol-gel materials have been prepared by adding a spiropyran photochromic dye to a solution of ethoxy silane monomers containing non-reacting ethyl radicals. After polymerization, normal photochromism (i.e., colored material upon UV irradiation) is obtained in the resulting matrix. The sol-gel matrix hinders the organic molecule rotations, thus giving two stable states, which can be reversibly switched by UV and green-blue irradiation respectively.If these materials are attached to optical fibers, the properties of the light throughput may be modified. Simple fiber-optic/photochromic devices made of two optical fibers placed in a V-groove removable connector have been prepared. Once cured, these devices behave as optically addressed variable delay generators. The same devices can be used for preparing simple optical switches and routing systems.     

Optical Chemical Sensors Based on Sol-Gel Materials: Recent Advances and Critical Issues

The use of the sol-gel process to produce materials for optical chemical sensors and biosensors is attracting considerable interest. This interest derives mainly from the design flexibility of the sol-gel process and the ease of fabrication. In most applications the sol-gel material is used to provide a microporous support matrix in which analyte-sensitive species are entrapped and into which smaller analyte molecules may diffuse. Sensors based on entrapped organic and inorganic dyes, enzymes and other biomolecules have been reported. A range of sensor configurations has been employed, including monoliths, thin films, as well as more elaborate structures. In this paper a selection is presented of recent significant developments in optical chemical sensors which employ solgel-derived materials. These developments include the tailoring of sol-gel materials to optimise sensor response, advanced waveguide structures and novel probe-tip sensors. Those issues which remain critical to the eventual deployment of sol-gel sensors are examined. In particular, the problems of leaching, microstructural stability, diffusion-limited response time, and susceptibility to interferents are discussed and some solutions proposed.     

Photophysical and photochemical effects of dye binding

Abstract— A discussion is given of the photophysical and photochemical consequences of the binding of dyes and of pigments of biological importance to polymeric substrates. The modification of the photochemical properties induced by dye binding can in large part be ascribed to the known changes in photophysical properties of dyes engendered by such interactions. Principally, these involve enhanced formation of metastable species of dye molecules and decreased opportunity for self-quenching. In photochemical terms, dye binding thus enhances susceptibility to photoreduction, causes an increase in the quantum yield of photoreduction with increasing concentration of bound dye, and induces enhanced ability to act as a sensi-tizer in photoreduction. Paradoxically, dye binding decreases the ability of the bound dye to act as a sensitizer in photoxidation.     

Optical Alignment of Organic Dopants in a Solid Gel Matrix: Dispersed and Grafted Rhodamine B Molecules

We study herein the rotational mobility of organic dye molecules and their ability to align on a strong optical electric field when they are encaged in the pores of an inorganic silica xerogel matrix. We compare the case of dye molecules simply dispersed in the pores of the gel—and possibly held by hydrogen bonds—to the case of molecules chemically grafted on the inner surface of these pores through covalent bonds. The study is led on hybrid silicon-zirconium based inorganic matrices doped with organic rhodamine B molecules. The stronger holding of the dopants when these are grafted to the matrix enhances the molecular alignment—and thus the induced anisotropy—as well as the remanence of this alignment. Furthermore, we show that submitting the samples to a supplementary drying at higher temperature tends to increase both the alignment anisotropy and its stability. We explain these results in terms of mobility of the molecules, in relation to their immediate environment.     

Diketopyrrolopyrrole-based functional supramolecular polymers: next-generation materials for optoelectronic applications

The very concept of dye and pigment chemistry that was long known to the industrial world underwent a radical revision after the discovery and commercialization of dyes such as mauveine, indigo, and so on. Apart from their conventional role as coloring agents, organic dyes, and pigments have been identified as indispensable sources for high-end technological applications including optical and electronic devices. Simultaneous with the advancement in the supramolecular chemistry of π-conjugated systems and the divergent evolution of organic semiconductor materials, several dyes, and pigments have emerged as potential candidates for contemporary optoelectronic devices. Of all the major pigments, diketopyrrolopyrrole (DPP) better known as the ‘Ferrari Pigment’ and its derivatives have emerged as a major class of organic functional dyes that find varied applications in fields such as industrial pigments, organic solar cells, organic field–effect transistors, and in bioimaging. Since its discovery in 1974 by Farnum and Mehta, DPP-derived dyes gained rapid attention because of its attractive color, synthetic feasibility, ease of functionalization, and tunable optical and electronic properties. The advancement in supramolecular polymerization of DPP-based small molecules and oligomers with directed morphological and electronic features have led to the development of high performing optoelectronic devices. In this review, we highlight the recent developments in the optoelectronic applications of DPP derivatives specifically engineered to form supramolecular polymers.     

Scratch and Abrasion Resistant Coatings on Plastic Lenses—State of the Art,Current Developments and Perspectives

The manufacturing of ophthalmic lenses is one of the most important markets worldwide and, therefore, strong research efforts are undertaken to continuously improve the quality of the products, either silicate glasses or organic polymer lenses. Hybrid sol-gel based materials play a major role in this highly competitive field and have contributed significantly to the commercial success of the organic base materials. Recent developments concern fast curing and patternable coatings that might soon become part of this business. The compatibility of hybrid sol-gel materials either with organic dyes or with inorganic vacuum borne coatings offers further possibilities to develop highly sophisticated lenses meeting not only customer needs like perfect corrective function, high optical quality and protection, but also high durability as well as cosmetic and decorative aspects. An overview and a few recent developments are outlined below.     

A fast convenient method to prepare hybrid sol-gel materials with low volume-shrinkages

We present a simple and fast method for the synthesis of polyacrylates-silica hybrid materials with significantly low volume shrinkages through the sol-gel reactions of tetraethyl orthosilicate and 2-hydroxyethyl methacrylate along with the free-radical polymerization of the acrylate monomer. The volume shrinkage from the processible sol to the final product was about 6–20% for the hybrid materials having the silica contents up to about 50 wt-%. As a result of the low shrinkage, crack-free, transparent and monolithic hybrid materials of relatively large sizes can be prepared within a short period of 6 to 12 hours. The formation of covalent bonding between the organic and the silica components in the hybrid materials was demonstrated. Thermal stability of the polyacrylate component in the hybrid materials were found to be higher than that of the bulk polymer. Other vinyl polymers such as poly(methyl methacrylate) and polyacrylonitrile have also been incorporated into the inorganic silica sol-gel matrix by using this method.     

Improvement in the Leaching Behavior of Dye-Doped Modified Silica Layers Coated onto Paper or Textiles

Leaching stability is important when refining paper or textile surfaces with sol-gel silica layers that contain incorporated dyes or other components. First studies show a simultaneous increase in dye and Si concentration in the wash-out solution, indicating that the gradual dissolution of the complete composite layer plays an important role in the leaching process. The leaching stability of silica layers containing incorporated model dyes Aniline Yellow and Acid Orange 10 on different flexible substrates (cellulose paper, polyamide and polyester fabrics) could be improved in a number of different ways: (i) pretreating the substrate with coupling agents such as epoxyalkyl-silanes, (ii) fixing the dye within the silica layer by mixing it with alumina or alkylammonium compounds, and (iii) chemically fixing the dye by bonding it covalently to the silica matrix.     

SYNTHESIS AND OPTICAL PROPERTIES OF A NOVEL ORGANIC/INORGANIC HYBRID NONLINEAR OPTICAL POLYMER VIA SOL-GEL PROCESS*

A new organic/inorganic hybrid nonlinear optical (NLO) material was developed by the sol-gel process of analkoxysilane dye with tetraethoxysilane. A NLO moiety based on 4-nitro-4'-hydroxy azobenzene was covalently bonded tothe triethoxysilane derivative, i.e. γ-isocyanatopropyl triethoxysilane. The preparation process and properties of the sol-gelderived NLO polymer were studied and characterized by SEM, FTIR, ~1H-NMR, UV-Vis, DSC and second harmonicgeneration (SHG) measurement. The results indicated that the chemical bonding of the chromophores to the inorganic SiO_2networks induces low dipole alignment relaxation and preferable orientational stability. The SHG measurements also showedthat the bonded polymer film containing 75 wt% of the akoxysilane dye has a high electro-optic coefficient (r_(33)) of 7.1 pm/Vat 1.1 μm wavelength, and exhibit good SHG stability, the r_(33) values can maintain about 92.7% of its initial value at roomtemperature for 90 days, and can maintain about 59.3% at 100℃ for 300 min.s     

Compound Specific Radiocarbon (14C) Dating of Our Colorful Past: from Theory to Practice

For generations, humanity has preserved customs, places, objects, artistic expressions, and values – our cultural heritage. The use of color on cultural heritage objects is ubiquitous and found on artefacts from prehistoric rock art to present day contemporary artworks. The chemical identification of the colored materials used within an artwork often provides information about the work's origin. At the simplest level, a comparison of the materials present with information on their first date of discovery indicates the earliest possible period in which the colored artefact was created. More precise constraints on the date of creation can be provided by radiocarbon (¹⁴C) dating, however until today no such analysis has ever been conducted on the compounds responsible for the object's color. The analysis of natural organic dyes and pigments is challenging, as the limited sampling access, their low concentrations and presence in highly complex matrix, are all major challenges to be overcome. The separation of intermingled carbon sources is without question the most difficult problem, yet feasible with the help of compound specific radiocarbon analysis (CSRA). Here, we discuss the potential of radiocarbon dating isolated natural organic dyes and pigments and explore new routes to date cultural heritage objects.     

IR-Luminescent Molecules in Hybrid Materials

In the present work we report on steady-state and dynamical optical properties of four polymethine dye molecules absorbing in the near infrared (IR) region (0.8–1.1 m) and emitting around 1.2 m. The molecules are embedded in organically modified silicate (ORMOSIL) material synthesized by a sol-gel method. The investigated samples were prepared as films, deposited on glass substrates. Steady-state absorption and emission measurements have been accomplished for the chromophores in solution as well as in hybrid organic/inorganic films in order to determine the effect of the solid cage on the optical properties of the chromophore. To better understand the influence of the solid network, we also measured for some of the investigated molecules emission transients with femtosecond time resolution. An estimation of the emission quantum yield of the IR dye molecules in a glassy matrix is also given. The kinetic results are sensitive to guest-host interactions.     

Synthesis, characterization and flame retardant of UV-curable hybrid coatings containing SiO2–P2O5–B2O3 via sol–gel method

A ternary sol containing silicon, phosphorus and boron modified by ??-methacryloxypropyltrimethoxysilane was synthesized by sol?Cgel method. The ternary sol was incorporated into the organic matrix and UV-curable organic/inorganic hybrid coating materials were obtained. Hardness, transmittance, haze, cross-cut adhesion and abrasion resistance results showed that the mechanical properties of the hybrid coatings improved effectively with no comprising on optical properties by increasing sol content. Scanning electron microscopy and Energy Dispersive X-ray spectrometer studies indicated that inorganic particles were homogenously dispersed in the organic matrix. The flame retardancy of the UV-curable coatings was investigated by thermogravimetric analysis and microscale combustion calorimeter. The results showed that the incorporation of sol into the organic network led to an improvement in the thermal stability and flame retardancy of the hybrid coating materials. It is a desirable achievement to improve simultaneously both flame retardancy and mechanical properties of the coatings.     

Organic sol-gel materials for second-order nonlinear optics based on melamines

A series of all organic nonlinear optical (NLO) sol-gel materials based on melamines and an azobenzene dye (Disperse Orange 3; DO3) have been investigated. Different contents of DO3 were covalently bonded with the melamine-based organic network via condensation of amino and methylol groups. The optically clear samples exhibited second-order optical nonlinearity (second-harmonic coefficient d₃₃) = 35.4 and 11.5 pm/V at 1064 and 1542 nm, respectively) after poling and curing at 220°C for 1 h. Thermal behavior of these organic NLO sol-gel systems was studied by temperature-dependent dielectric relaxation. The results indicate that the incorporation of rigid NLO-active chromophore into the melamine-based matrix leads to high rigidity and dense packing of the organic network. Subsequently, higher glass transition temperatures were obtained for the organic NLO sol-gel material with higher DO3 content. The influence of composition on the temporal stability at 100°C was also investigated. Temporal stability at 100°C was studied as a function of system composition. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2503–2510, 1999     

Sol-gel derived hybrid polymers as alternative materials for optical data storage in the frequency domain

Sol-gel derived hybrid organic-inorganic materials show attractive properties as alternative media for optical data storage in the frequency domain. Doping of the matrix is easily achieved by dissolving different types of organic dyes in appropriate amounts in the clear sols, obtained via cohydrolysis and -condensation of 3-glycidoxypropyl-trimethoxysilane and aluminium-tri (secondary butylate).By evaporating volatile solvents and drying the resulting gel at room temperature, the dyes are trapped in the hybrid network. Surprisingly narrow spectral holes in the absorption bands of the dyes were generated by photophysical or photochemical hole-burning at very low temperatures. For dihydroxyanthraquinone/YbCl₃-complexes the measured holewidth of 2,1 GHz at 3,94 K is about 1/5 of that found for the same complex in an ethanol/methanol glass.     

溶胶-凝胶法制备二氧化钛纳米粒子及在光固化体系中的稳定分散

选用3种不同的稳定剂,乙酰丙酮(acac),异丙氧基三(焦磷酸二辛酯)钛(TTPO)和可聚合有机磷酸酯(MAP),采用钛酸四正丁酯(TBT)通过溶胶-凝胶法合成了一系列二氧化钛溶胶,并与树脂/单体相混合,制备成有机-无机杂化光固化涂料.利用FT-IR监测了TBT水解缩合形成溶胶的过程及杂化体系的光聚合过程.杂化固化膜SEM结果显示,在合成溶胶过程中添加不同的稳定剂对杂化固化膜中无机粒子粒径尺寸等形态有显著影响,其中使用TTPO作为稳定剂得到的无机粒子分散最均匀,粒径最小,约20 nm.物理性能测试表明光固化杂化膜在硬度和柔韧性方面都有明显的改善.     

Antenna behavior of donor–acceptor dye‐loaded novel supramolecular framework hosts

New guest dye cations within the channel cavities of supramolecular hosts are studied. The guest organic dyes are intercalated in the supramolecular hosts by a coprecipitation reaction to give new dye‐sensitizer coordination polymers. The absorption spectra for the dye molecules within the supramolecular hosts show intense bands in the region from 500 to 700 nm due to the presence of the dyes within the parallel channels in the monomeric forms. The properties of the resulting colored polymers were investigated by IR, UV–vis, fluorescence spectra and X‐ray powder diffraction, indicating the excitation energy transfer from neutral red or pyronine as donors to methylene blue or thionine as acceptors within a supramolecular system filled with a mixture of both dyes. The wide‐ranging tenability of these highly organized materials offers fascinating new possibilities for exploring excitation energy transfer phenomena, and challenges for developing new photonic devices. Copyright © 2005 John Wiley & Sons, Ltd.     

Hybrid materials for optics and photonics

The interest in organic-inorganic hybrids as materials for optics and photonics started more than 25 years ago and since then has known a continuous and strong growth. The high versatility of sol-gel processing offers a wide range of possibilities to design tailor-made materials in terms of structure, texture, functionality, properties and shape modelling. From the first hybrid material with optical functional properties that has been obtained by incorporation of an organic dye in a silica matrix, the research in the field has quickly evolved towards more sophisticated systems, such as multifunctional and/or multicomponent materials, nanoscale and self-assembled hybrids and devices for integrated optics. In the present critical review, we have focused our attention on three main research areas: passive and active optical hybrid sol-gel materials, and integrated optics. This is far from exhaustive but enough to give an overview of the huge potential of these materials in photonics and optics (254 references).