Conjugated materials, nonlinear optical properties

The linear and nonlinear optical properties of one-dimensional conjugated polymers contain a wealth of information closely related to the structure and dynamics of the ir-electron distribution and to their interaction with the lattice distorsions. The existing values of the nonlinear susceptibilities indicate that these materials are strong candidates for nonlinear optical devices in different applications. However their time response may be limited by the diffusion time of intrinsic conjugation defects and the electron-phonon coupling. Since these defects arise from competition of resonant chemical structures the possible remedy is to control this competition without affecting the delocalization. The understanding of the polymerisation process is consequently essential. 

Tetraethynylethene molecular scaffolding has provided conjugated materials with properties that are greatly enhanced upon incorporating functional arene units. Indeed, third-order nonlinear optical properties are increased by aryl groups photochemical cis-trans isomer-... 

In this section the electronic structure of conjugated polymers is discussed. They form a special class of materials with particular types of excitations (such as the solitons) and properties, introduced briefly in Chapter 11. These problems are discussed here essentially in relation to the spectroscopic properties. The related but distinct subject of electrical conductivity is treated in Section IV. To set the scene, we first present some typical results visible absorption and emission spectra and resonance Raman spectra. We consider the theoretical issues in Section III.B, then return to the meaning of the experimental results in Section III.C. The interesting nonlinear optical properties of CPs will be considered in Section III.D. These sections are concerned with electronic states within the gap or near the band edges the structure (i.e., the dispersion relations) of valence and conduction bands is also of theoretical interest and is considered in Section III.E. 

Conjugated polymers satisfy these requirements and have thus emerged as the most widely studied materials for their susceptability. Some of the examples of conjugated polymers, that have been studied for their third order NLO properties, are polydiacetylenes, poly-p-phenylenevinylenes and polythiophenes. However, CVD has only been used in the case of poly-p-phenylenevinylenes (PPV) [section 3.4], although values have not been reported. An excellent review of third order nonlinear optical properties of PPV in general, can be found in literature. Recently, McElvain et al. ° reported the values of CVD polyazomethines to be... 

B. Kirtman, in Nonlinear Optical Materials Theory and Modeling, S. P. Kama and A. T. Yeates, Eds., American Chemical Society, Washington, DC, 1996, pp. 58-78. Calculation of Nonlinear Optical Properties of Conjugated Polyenes. 

A.F. Garito, J.R. Heflin, K.Y. Wang and O. Zamani-Khamiri, Enhancement of nonlinear optical properties of conjugated linear chains through lowered qmmetry, in "Organic Materials for Non-Linear Optics", R.A. Hann and D. Bloor, eds., Roy. Soc. Chem., London, 1989. 

The linear and nonlinear optic properties of organic materials, including a -conjugated molecular polymers, make it possible to develop numerous technological and industrial applications of these systems. The applications in the field... 

Nonlinear Optical Properties of n-Conjugated Materials Hari Singh Nalwa... 

---