Photoinduced motions in azo-containing polymers.

Linear and Nonlinear Optical Properties of Photochromic Molecules and Materials.

All optical fabrication of Surface Relief Grating (SRG) on azobenzene functionalized polymer films is reviewed in this article. The uniqueness of the single step erasable photofabrication of large amplitude surface relief structures on azo polymer films is mainly due to the photoisomerization and photoanisotropic behavior of the azobenzene group. The design and synthesis of several classes of suitable azobenzene functionalized polymers for the SRG formation is presented. Experimental studies are carried out in a systematic manner to understand the chemical and physical intricacies involved in the SRG formation process. Structural requirements and their limitations for the efficient fabrication of SRGs on azo functionalized polymer films are also discussed. Understanding the fundamental mechanism of SRG formation on the azo functionalized polymer films enables us to make use of these structures in a variety of applications.

Surface relief structures on azo polymer films

The change in shape inducible in some photo-reversible molecules using light can effect powerful changes to a variety of properties of a host material. The most ubiquitous natural molecule for reversible shape change is the rhodopsin–retinal protein system that enables vision, and this is perhaps the quintessential reversible photo-switch. Perhaps the best artificial mimic of this strong photo-switching effect however, for reversibility, speed, and simplicity of incorporation, is azobenzene. This review focuses on the study and application of reversible changes in shape that can be achieved with various systems incorporating azobenzene. This photo-mechanical effect can be defined as the reversible change in shape inducible in some molecules by the adsorption of light, which results in a significant macroscopic mechanical deformation of the host material. Thus, it does not include simple thermal expansion effects, nor does it include reversible but non-mechanical photo-switching or photo-chemistry, nor any of the wide range of optical and electro-optical switching effects for which good reviews exist elsewhere.

Photo-mechanical effects in azobenzene-containing soft materials.

A model for the formation of holographic surface relief gratings in azobenzene functionalized polymers is presented. Forces leading to migration of polymer chains upon exposure to light in the absorption band of the azo chromophore are attributed to dipoles interacting with the gradient of the electric field present in the polymer material. Efficient trans–cis cycling in the azobenzenes allows cooperative movement of the chromophores under the influence of gradient forces.

Gradient force: The mechanism for surface relief grating formation in azobenzene functionalized polymers

Poly{(4-nitrophenyl)-3-[N-[2-(methacryloyloxy)ethyl]carbazolyl]]diazene} was prepared and its photoinduced birefringence, diffraction grating, and photorefractive asymmetric two-beam gain coupling were studied. The monomer was obtained by performing azo coupling in a two-phase water−dichloromethane system in the presence of a phase transfer catalyst. Photoinduced birefringence of up to 0.09 was observed and diffraction efficiencies of up to 25% were obtained, with atomic force microscopy studies revealing that the grating profile exhibited a sinusoidal shape. Asymmetric two-beam coupling is observed, indicating photorefractive properties, but the energy transfer phenomena are more complex, involving also diffraction by the photoinduced gratings. The combination of these three optical propertiesphotoinduced birefringence, surface gratings, and two-beam couplingis believed to be unique and may eventually produce an all-optical device built of a single polymer film.

Synthesis and Optical Properties of Poly{(4-nitrophenyl)-[3-[N-[2-(methacryloyloxy)ethyl]- carbazolyl]]diazene}

Poly{(4-nitrophenyl)-3-(N-(2-(methacryloyloxy)ethyl)carbazolyl))diazene}was prepared and its photoinduced birefringence, diffraction grating, and photorefractive asymmetric two-beam gain coupling were studied. The monomer was obtained by performing azo coupling in a two-phase water- dichloromethane system in the presence of a phase transfer catalyst. Photoinduced birefringence of up to 0.09 was observed and diffraction efficiencies of up to 25% were obtained, with atomic force microscopy studies revealing that the grating profile exhibited a sinusoidal shape. Asymmetric two-beam coupling is observed, indicating photorefractive properties, but the energy transfer phenomena are more complex, involving also diffraction by the photoinduced gratings. The combination of these three optical propertiessphotoinduced birefringence, surface gratings, and two-beam couplingsis believed to be unique and may eventually produce an all-optical device built of a single polymer film.

Poly{(4-nitrophenyl)-(3-(N-(2-(methacryloyloxy)ethyl)- carbazolyl))diazene}

Surface relief diffraction gratings inscribed on azobenzene‐containing polymers are designed to act as light couplers into slab waveguides. The gratings are inscribed both directly in poly{4‐[2‐(methacryloyloxy)ethyl]azobenzene} (pMEA) waveguide material, and in an azopolymer cladding layer applied to polyimide, silicon nitride, and silicon oxynitride films. Input and output coupling of both 633 and 830 nm light is observed in the waveguides.

J. Paterson

Papers

Synthesis and Optical Properties of Poly{(4-nitrophenyl)-[3-[N-[2-(methacryloyloxy)ethyl]- carbazolyl]]diazene}

Poly{(4-nitrophenyl)-(3-(N-(2-(methacryloyloxy)ethyl)- carbazolyl))diazene}

Optically inscribed surface relief diffraction gratings on azobenzene-containing polymers for coupling light into slab waveguides