Structure-property relationships nonlinear optics

Fig. 8. Examples of some of the donor-acceptor substituted TEEs prepared for the exploration of structure-property relationships in the second- and third-order nonlinear optical effects of fully two-dimensionally-conjugated chromophores. For all compounds, the second hyperpolarizability y [10 esu], measured by third harmonic generation experiments in CHCI3 solution at a laser frequency of either A = 1.9 or 2.1 (second value if shown) pm is given in parentheses. n.o. not obtained...

Structure-Property Relationships In Nonlinear Optical Tetraethynylethenes... 

Gray, G. M. Lawson, C. M. Structure-Property Relationships in Transition Metal-organic Third-order Nonlinear Optical Materials. In Optoelectronic Properties of Inorganic Compounds, Roundhill, D. M., Fackler, J. P., Jr., Eds. Plenum New York, 1999 pp 1-27. 

R, R. Tykwinski, U. Gublei R, E. Martin, F. Diederich, C. Bosshard, P. Gunter, Structure-Property Relationships in Third-Order Nonlinear Optical Chromophores , J. Phys. Chem B. 1998,102, 4451-4465. 

The electronic structure of fluorenes and the development of their linear and nonlinear optical structure-property relationships have been the subject of intense investigation [20-22,25,30,31]. Important parameters that determine optical properties of the molecules are the magnitude and alignment of the electronic transition dipole moments [30,31]. These parameters can be obtained from ESA and absorption anisotropy spectra [32,33] using the same pump-probe laser techniques described above (see Fig. 9). A comprehensive theoretical analysis of a two beam (piunp and probe) laser experiment was performed [34], where a general case of induced saturated absorption anisotropy was considered. From this work, measurement of the absorption anisotropy of molecules in an isotropic ensemble facilitates the determination of the angle between the So Si (pump) and Si S (probe) transitions. The excited state absorption anisotropy, rabs> is expressed as [13] ... 

In this paper, an overview of the origin of second-order nonlinear optical processes in molecular and thin film materials is presented. The tutorial begins with a discussion of the basic physical description of second-order nonlinear optical processes. Simple models are used to describe molecular responses and propagation characteristics of polarization and field components. A brief discussion of quantum mechanical approaches is followed by a discussion of the 2-level model and some structure property relationships are illustrated. The relationships between microscopic and macroscopic nonlinearities in crystals, polymers, and molecular assemblies are discussed. Finally, several of the more common experimental methods for determining nonlinear optical coefficients are reviewed. 

Although both the ab-initio derivative method and the semi-empirical sum-over-states approach have been used with some success to predict qualitative trends, they are not sufficiently developed to have predictive capabilities for structure-property relationship. Clearly, there is a need to develop semi-empirical theoretical methods which can reliably be used to predict, with cost-effectiveness and with reasonable computational time, molecular and polymeric structures with enhanced optical nonlinearity. 

In this paper it has been attempted to provide an introductory overview of some of the various nonlinear optical characterization techniques that chemists are likely to encounter in studies of bulk materials and molecular structure-property relationships. It has also been attempted to provide a relatively more detailed coverage on one topic to provide some insight into the connection between the macroscopic quantities measured and the nonlinear polarization of molecules. It is hoped that chemists will find this tutorial useful in their efforts to conduct fruitful research on nonlinear optical materials. 

In polytriacetylenes (Fig. 19) the conjugation across the backbone is weaker than for polyenes. Conversely, the PTAs are stable under normal laboratory condition and show no degradation over months, which makes them an interesting candidate for applications. Furthermore, the chemical synthesis allows to have a well defined number of monomer units and to attach definite functional groups enabling the study of the structure-property relationships in nonlinear optics. 

Nonlinear optical (NLO) materials based on metal complexes have been investigated, particularly from the viewpoint of structure-property relationships for guiding of molecular design. Mono-, di-, and tetranuclear Ru complexes containing 2,2 - -phenylene-bis(imidazo[4,5-/]-phenanthroline) (L24) have been synthesized and examined with regard to NLO properties (Scheme ll).54 It has been reported that the magnitude of the hyperpolarizability of the tetranuclear Ru complex is approximately four times larger than that of the mononuclear complex. 

Quantum mechanical analysis based on a simple two-level model [22] and bond-order alternation (BOA) principle exploiting aromaticity [23] have worked surprisingly well in providing useful structure/property relationships for the design of chromophores with ever improving molecular hyperpolarizability. Table 1 provides some representative examples with improved molecular optical nonlinearity developed over the past decade. It has been shown that very large nonlinearities... 

This synthesis work was not only aimed at obtaining a better knowledge of the structure-properties relationships, but also at designing either polymers with reduced viscosity and improved response time, suitable for display applications, or polymers bearing in their side chains an electron donor-IT system-electron acceptor moiety for second order nonlinear optics. 

Micron- and submicron-scale lateral structures of optically nonlinear organic films comprised of substituted trons-stilbene derivatives (Ri = OCH3, R2 = CN) was characterized [45]. Second harmonic generation (SHG), optical microscopy, and atomic force microscopy (AFM) were used in this investigation. The third-order nonlinear optical properties and two-photon absorption ofdifferent types of stilbene derivatives (D-tt-D, A-7t-A, D-7t-A) were investigated [46]. Using the INDO/CI method, the UV-vis spectra were explored and the position and strength of the two-photon absorption were predicted by sum-over-states expression. Relationships of the structures, spectra, and nonlinear optical properties have been examined. Two-photon absorption spectra (650-1000 nm) of a series of asymmetrically substituted stilbenoid chromophores... 

P.A. Thomas, A. Baldwin, R. Dupree, P. Blaha, K. Schwarz, A. Samoson, Z.H. Gan, Structure-property relationships in the nonlinear optical crystal KT10P04 investigated using NMR and ab initio DFT calculations, J. Phys. Chem. B 108 (2004) 4324-4331. 

Most of the reported conjugated polymers with nonlinear optical or electrical activities are carbon-carbon conjugated systems, such as the extensively studied polyenes (e.g., polyacetylenes [15], polydiacetylenes [16,17], poly-/ -phenylenes) and heteroaromatic polymers (e.g., polypyrroles, polythiophenes, polycarbazoles, polyanilines) [18]. The synthetic methods, applications, and the structure-property relationships of these polymers have also been substantially investigated [19-21]. 

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