Nonlinear chromophore-functionalized

Recently photorefractivity in photoconductive polymers has been demonstrated (92—94). The second-order nonlinearity is obtained by poling the polymer doped with a nonlinear chromophore. Such a polymer may or may not be a good photoconductor. Usually sensitizers have to be added to enhance the charge-generation efficiency. The sensitizer function of fuUerene in a photorefractive polymer has been demonstrated (93). 

This chapter concentrates on the design of efficient dipolar NLO chromophores and the different approaches for their incorporation in non-centrosymmetric materials, including guest-host polymer systems, chromophore-functionalized polymers (side-chain and main-chain), cross-linked chromophore-macromolecule matrices, dendrimers, and intrinsically acentric self-assembled chromophoric superlattices. The different architectures will be compared together with the requirements (e.g., large EO coefficient, low optical absorption, high stability, and processability) for their incorporation into practical EO devices. First, a brief introduction to nonlinear optics is presented. 

Samyn et al. reported preparation of chiral chromophore-functionalized polybinaphthalenes for nonlinear optics. These polymers were... 

X is hexyl. The authors report that the typical tree-like macromolecular architecture of these molecules gives rise to a unique behavior in the glass transition temperature as well as in nonlinear optical properties. The nonlinear optical response shows a continuous increase in function depending on the chromophore content. In this way, the nonlinear optical properties can be increased in a way that is not possible with other chromophore-functionalized polymer materials.By attaching chromophores as side chains to the rigid non bendable backbone a treelike structure with flexible branches forms. 

Syntheses and characterization of three fully functionalized photorefractive polymethacrylates containing different chromophores were reported Carbazole and nonlinear optics-functionalized methacrylate... 

This method has also been used for the synthesis of defined polysilanes in some applications. For example, Li et al. applied the polymerization of masked disilenes to synthesize an aryl substituted diazene chromophore functionalized polysilane with nonlinear optical properties [40]. 

The physical properties of the expanded radialenes were greatly enhanced upon donor functionalization, leading to the stable derivatives 76-78 with fully planar conjugated rr-chromophores [110]. These compounds exhibit large third-order nonlinear optical coefficients, can be reversibly reduced or oxidized, and... 

A synthesis and physicochemical characterization, including molecular second-order nonlinear optical properties, of new push-pull-based chromophores 170 properly functionalized for polymerization and containing oxadiazole rings were reported <2002J(P2)1791>. 

The material system is a Langmuir-Blodgett film of the S enantiomer of a chiral polymer deposited on a glass substrate. The polymer is a poly(isocyanide)30 functionalized with a nonlinear optical chromophore (see Figure 9.14). In this particular system the optical nonlinearity and chirality are present on two different levels of the molecular structure. The chirality of the polymer is located in the helical backbone whereas the nonlinearity is present in the attached chromophores. Hence, this opens the possibility to optimize both properties independently. 

The developed model was applied to the EPS experiment (Fig.lb) to extract information on the water dynamics. Similar to the previous report [17], the EPS function decreases rapidly at a time scale of -0.5 ps, then raises again at -2 ps, and finally falls off to zero. The EPS functions acquired while keeping the delays tn (empty circles) and t23 (solid circles) fixed [20], are shifted along the vertical axis which is a consequence of the relatively short excited-state lifetime (700 fs). The peak in the EPS function around -2 ps is explained in the framework of our model as arising from interference between the chromophore and solvent responses. The delicate balance between phases of genuinely nonlinear and thermal contributions as the delay t12 between the two excitation pulses is increased, leads to the enhancement of the integrated signal that is measured in the EPS experiment. 

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. 

The hb-PAEs of hb-P13 and hb-P15 contain NLO-active azo-functionalities, which are soluble, film-forming, and morphologically stable (Tg > 180 °C). Their poled films exhibited high SHG coefficients ( 33 up to 177pm/V), thanks to the chromophore-separation and site-isolation effects of the hyperbranched structures of the polymers in the three-dimensional space (Table 5) [28]. The optical nonlinearities of the poled films of the polymers are thermally stable with no drop in d33 observable when heated to 152 °C (Fig. 8), due to the facile cross-linking of the multiple acetylenic triple bonds in the hb-PAEs at moderate temperatures (e.g., 88 °C). 

The area of molecular nonlinear optics has been rejuvenated by efforts to investigate three-dimensional multipolar systems, functionalized polymers as optoelectronic materials, near infrared optical parametric oscillators and related aspects.71 There have been some advances in chromophore design for second-order nonlinear optical materials 72 these include onedimensional CT molecules, octopolar compounds and organometallics. Some of the polydiacetylenes and poly(/>-phenylenevinylene)s appear to possess the required properties for use as third-order nonlinear optical materials for photonic switching.73... 

An alternative quasiparticle description of the optical response is possible using the nonlinear exciton equations (NEE) (39). The response function is then represented in terms of one-exciton Green functions and exciton-exciton scattering matrix. Four coherent ultrafast 2D techniques have been proposed (16,17), and computer simulations of the 2D response were performed for model aggregates made out of a few two-level chromophores. 

Examples of helix-forming polymers are poly(isocyanides) and poly(glutamates). The repeat imits of these polymers are shown in Figure 7. For poly(isocyanides), each carbon atom of the polymer backbone was functionalized with a nonlinear optical chromophore (Figure 7, I). Because of large steric interactions between the... 

---