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.

/pdf/optical-negative-index-metamaterials-2q5qafgl3m.pdf

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

In this paper the concept and design of infrared cloaking using nanosphere dispersed liquid crystal (NDLC)matematerial in cylindrical geometry is presented for TM polarization of incident light. The inuence of materiallosses on the cloaking eciency is discussed. The loss can be tuned by changing design parameters. 1. CLOAKING EFFECT  AN OUTLINE In 1968 by Veselago in his seminal paper 1 has introduced the concept of metamaterials by showing that Maxwellequations allow for the existence of propagating solutions corresponding to negative values of refractive index.However, this concept was not further explored because materials with such unusual properties can not befound in nature. The interest in the eld of metamaterials started to grow steadily since the rst experimentalrealization by Pendry 2 in 1998. The used metamaterial, composed of thin metal wires and split-ring resonators,oered no possibility of tuning. Since the rst experimental realization of metamaterial behavior many dierentapproaches to obtain the negative eective refractive index were invented. An incomplete survey of some of therecent result can be found in a review paper.

Optimization of cloak effect in nanosphere dispersed liquid crystal metamaterial

We present an overview of recent results obtained in pure and nano-dopant modified liquid crystals which possess extraordinarily ultrafast nonlinear nonlinearities for all-optical processing with lasers of wide ranging temporal and spectral characteristics.

Liquid crystals nonlinear optics — CW to femtoseconds all-optical signal processing

Theoretical analysis of photorefractivity in dye-doped nematic liquid crystal film is discussed. Analytical solutions of refractive index distribution and the first order diffraction efficiency are presented. The relationship between the diffraction efficiency and the applied DC voltage shows very good agreement to the experimental result in photorefractive region.

Orientational photorefractive effect in photosensitive-dye doped nematic liquid crystals

We have fabricated 1-, 2- and 3-D photonic crystalline structures in polymer dispersed nematic and isotropic phase liquid crystals. It is observed that a particular mixture of isotropic liquid crystals and the photo-polymer will also polymerize and phase separate, forming high quality optical gratings, just as typical nematic liquid crystals. Liquid crystal droplet sizes obtained could be as small as a few 10’s of nm, i.e., nano-droplets. The resultant structure exhibits excellent optical qualities, and high efficiency Bragg diffraction properties.

Direct Optical Holographic Fabrication of Photonic Crystals in Polymeric Dispersed Nematic and Isotropic Liquid Crystals

A near-IR metamaterial having a tunable index of refraction from negative, through zero, to positive values has been proposed. Liquid crystal layers are incorporated both as a superstrate and a substrate onto a conventional NIM. Tuning the permittivity of the liquid crystal layers controls the value of the effective permittivity in an averaging manner. Combined with proper magnetic resonances provided by a pair of silver strips separated by a thin layer of alumina, the effective index of refraction can be reconfigured between negative, zero, and positive values. The ability to vary the permittivity of the liquid crystal layers also provides a method to control the bandwidth of the negative index behavior.

/pdf/liquid-crystal-clad-metamaterial-with-a-tunable-negative-etc3abubh2.pdf

Iam-Choon Khoo

Papers

Optimization of cloak effect in nanosphere dispersed liquid crystal metamaterial

Liquid crystals nonlinear optics — CW to femtoseconds all-optical signal processing

Orientational photorefractive effect in photosensitive-dye doped nematic liquid crystals

Direct Optical Holographic Fabrication of Photonic Crystals in Polymeric Dispersed Nematic and Isotropic Liquid Crystals

Liquid crystal clad metamaterial with a tunable negative-zero-positive index of refraction