Functional Nonlinear Optical Dyes

Microscopy methods based on nonlinear optical phenomena that provide chemical information are a recent development. Infrared snm-frequency microscopy has been demonstrated for LB films of arachidic acid, allowing for surface-specific imaging of the lateral distribution of a selected vibrational mode, the asymmetric methyl stretch [60]. The method is sensitive to the snrface distribntion of the functional gronp as well as to lateral variations in the gronp environmental and conformation. Second-harmonic generation (SHG) microscopy has also been demonstrated for both spread monolayers and LB films of dye molecules [61,62]. The method images the molecular density and orientation field with optical resolution, and local qnantitative information can be extracted. 

Electrostatic self-assembly was combined with supramolecular chemistry to obtain inclusion complexes of a polymeric nonlinear optical (NLO) active dye and modified [3-cyclodextrin with induced chromophore orientation [37], The polyanion is a N,N-diallyl-aniline and sodium-2-acrylamido-2-methylpropanesulfonate copolymer functionalized with pendant azo group. The modified /i-cyclodextrin oligo-cation was obtained by treatment of hcptakis(6-dco y-6-iodo-/i-cyclodcxtrin) with excess pyridine. A linear polyamine, chitosan, was also combined with the polyanion, for comparison. Films were deposited on glass slides by dipping them alternatively in aqueous solutions of the cation and the polyanion. UV-visible spectra indicate dye aggregation and suggest the formation of an inclusion complex of the dye with the cyclodextrin, thus isolating the chromophores. 

Several papers and patents deal with the preparation of pyrrole-, indole-, and carbazole-derived dyes for application in organic laser device production, coloring of textiles and other materials, photography, analytical chemistry and physiological and organ function monitoring. Sulfonyl-substituted 2-[4-(dialkylamino)phenyliminomethyl]pyrrole dyes have been prepared, for example, 50-53, and their ultraviolet-visible (UV-Vis) absorptions, second-order nonlinear optical properties, and thermal stabilities have been described <1999TL2157>. 

Semi-empirical ZINDO SOS (sum over states) and ab initio quadratic response function (DDRPA) calculations on a series of D-A-substituted 7t-conjugated chromophores based on styryl benzothiazoles were used to aid in the design of dyes with high nonlinear optical properties <2004PCP495>. 

To illustrate the potential of LB films in nonlinear optics, two examples will be given to illustrate both quadratic- and cubic-order effects. The motivation for the first example came from early accounts of nonlinearity in a specific merocyanine dye molecule (49). No good crystals of this material are available, but an extremely large value of P was predicted on the basis of measurements with powdered samples. The reliability of such data is not high because powder efiSciency is a function of particle size distributions. The initial experiments were with a simple merocyanine dye alternated with o)-TA. However, the best results (50) were obtained by using organic superlattices based on the two molecules shown by Structures 4. la and 4. lb. 

Wostyn et al. [61] have reported the molecular nonlinear optical polarizability of lanthanate complexes containing stilbazolium ions. Their experimental results indicate that the hyperpolarizability is independent of the nature of the lanthanide, though the complex anion size is a function of the size of the ligand on the lanthanide cation. Andreu et al. [55] have synthesized a new chiral cyanine dye, 4 -[2-(methoxymethyl)pyrrolidinyl]-l-methylstilbazolium iodide (MPMS + I). They have reported that MPMS +1 exhibits phase-matched SHG with the efficiency of up to 80 times that of urea. 

The field of nonlinear optical (NLO) materials constitutes another area of research related to the synthesis of solvatochromic compounds. Asymmetric molecules possessing donor and acceptor substituents linked by a n-backbone exhibit large hyperpolarizabilities, being potential candidates far NLO materials with interesting properties. It is, therefore, not surprising that many solvatochi omic dyes also exhibit NLO properties. Solvatochromism is an important property in the design of NLO-functionalized macromolecules. ... 

The v cal integrated polymer device fabricated was a vartically stacked ED-polymer directional coupler (27). The nonlinear optical matmal used was a bisazo-dye functionalized EO polymer, 3RDCVXY. A standard REB process was used to fabricate the hybrid waveguides. Using die vertically stacked directional coupler, optical coupling similar to that of in-plane directional coupler was attained. 

Nowadays most colorants have the purpose to satisfy our aesthetical needs and, thus, thousands of dyes and pigments are produced on industrial scales. Nevertheless, nearly periodically new demands arise for so-called fimctional dyes whose tt-conjugated systems exhibit novel functionahties beyond aesthetical purposes. Optical brighteners or near-infrared absorbers are examples where even transparency in the visible spectrum is desired and dyes for nonlinear optics, holographic optical data storage and two photon absorption are further examples where the color properties of dyes are insignificantly related to the functional demands. 

Composite glasses prepared via the sol-gel technique are of high optical quality and large monolithic bulk forms can be made for various photonic functions [22,23,79,88,101-103] such as lasing, optical power limitation, nonlinear optical response, and so on. Figure 10.9 presents an example of a solid dye laser based on multiphasic composite monolith doped with BASF LFO-240 laser dye placed in optical resonator. 

As already mentioned, the organic dye rhodamine 6G was one of the first luminescent species studied, encapsulated in silica obtained by the SGM [4], It was also mentioned that one important observation at that time was related to the enhanced stability the organic molecule experienced in the xerogel host. Indeed, that first paper opened the road for a multitude of new optical materials involving organic functionalities. Sensors, dye lasers (visible and NIR), photochromic, nonlinear optics, and photovoltaic devices are some of the possible applications for these dyes containing OIH [11,92,93]. 

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