Following Sharpless' visionary characterization of several idealized reactions as click reactions, the materials science and synthetic chemistry communities have pursued numerous routes toward the identification and implementation of these click reactions. Herein, we review the radical-mediated thiol-ene reaction as one such click reaction. This reaction has all the desirable features of a click reaction, being highly efficient, simple to execute with no side products and proceeding rapidly to high yield. Further, the thiol-ene reaction is most frequently photoinitiated, particularly for photopolymerizations resulting in highly uniform polymer networks, promoting unique capabilities related to spatial and temporal control of the click reaction. The reaction mechanism and its implementation in various synthetic methodologies, biofunctionalization, surface and polymer modification, and polymerization are all reviewed.

Thiol–Ene Click Chemistry

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Artificially engineered metamaterials are now demonstrating unprecedented electromagnetic properties that cannot be obtained with naturally occurring materials. In particular, they provide a route to creating materials that possess a negative refractive index and offer exciting new prospects for manipulating light. This review describes the recent progress made in creating nanostructured metamaterials with a negative index at optical wavelengths, and discusses some of the devices that could result from these new materials.

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Optical negative-index metamaterials

4. Survey of Novel Multiphoton Active Materials 1257 4.1. Multiphoton Absorbing Systems 1257 4.2. Organic Molecules 1257 4.3. Organic Liquids and Liquid Crystals 1259 4.4. Conjugated Polymers 1259 4.4.1. Polydiacetylenes 1261 4.4.2. Polyphenylenevinylenes (PPVs) 1261 4.4.3. Polythiophenes 1263 4.4.4. Other Conjugated Polymers 1265 4.4.5. Dendrimers 1265 4.4.6. Hyperbranched Polymers 1267 4.5. Fullerenes 1267 4.6. Coordination and Organometallic Compounds 1271 4.6.1. Metal Dithiolenes 1271 4.6.2. Pyridine-Based Multidentate Ligands 1272 4.6.3. Other Transition-Metal Complexes 1273 4.6.4. Lanthanide Complexes 1275 4.6.5. Ferrocene Derivatives 1275 4.6.6. Alkynylruthenium Complexes 1279 4.6.7. Platinum Acetylides 1279 4.7. Porphyrins and Metallophophyrins 1279 4.8. Nanoparticles 1281 4.9. Biomolecules and Derivatives 1282 5. Nonlinear Optical Characterizations of Multiphoton Active Materials 1282

Multiphoton Absorbing Materials : Molecular Designs, Characterizations, and Applications

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

Optical bistability of a dielectric cladded thin film near the total internal reflection state: theory and experiment

Spatial optical solitons have been demonstrated at few mW powers in planar cells with a nematic liquid crystal and in the presence of an applied AC bias. The soliton is a channel waveguide able to confine a weak probe of equal polarization. Furthermore, since we deal with a nonresonant effect, the observed phenomena do not depend on wavelength and will be extended to the 1.3-1.5 /spl mu/m spectral region and to partially coherent beams. Finally, the use of an external voltage not only lowers the required power levels for self-confinement, but also enables an extra degree of control for all-optically reconfigurable interconnects.

Spatial solitons in voltage-biased nematic liquid crystals

We have observed an extraordinarily large optically induced refractive index change mechanism in aligned dye-doped nematic liquid crystal film. The effect is potentially useful for developing a new liquid crystal light valve or spatial light modulator, and for applications in other adaptive optics and coherent wave-mixing devices.

Optical nonlinear index coefficient of over 6 cm/sup 2//W in dye-doped nematic liquid crystals

We will discuss the reflection and transmission coefficients in the negative index materials. Based on the finite differential time domain approach, we obtain the reflection and transmission coefficients depending on permittivity and permeability at a fixed frequency. The transmissivity and reflectivity will be also examined. Simulation results are in good agreement with the theoretical ones. This technique can be easily extended to the multi-layered structure with negative index materials to design the optical system.

Finite difference time domain analysis for measuring transmission and reflection coefficients in negative index materials

This article reports a patented nonlinear fiber array [US Patent #5,589101-Khoo] faceplate device and several newly developed materials that are capable of spatial frequency discrimination and intensity dependent transmission In addition, because of the temporal range spanning nanosecond laser pulses to cw light sources, the device possesses response time and responses capable of self-action in such time scales This paper presents theoretical modeling of device operational principle and experimental demonstration results for cw and pulsed lasers

Iam-Choon Khoo

Papers

Optical bistability of a dielectric cladded thin film near the total internal reflection state: theory and experiment

Spatial solitons in voltage-biased nematic liquid crystals

Optical nonlinear index coefficient of over 6 cm/sup 2//W in dye-doped nematic liquid crystals

Finite difference time domain analysis for measuring transmission and reflection coefficients in negative index materials

Self-action cw-pulsed lasers and glare attenuators