Chromophoric superlattices

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. 

FIGURE 4.23 Schematic representation of (a) the three-step and (b) the two-step LbL assembly processes for chromophoric superlattices. 

Lin W, Lee TL, Lyman PF, Lee JJ, Bedzyk MJ, Marks TJ (1997) Atomic resolution X-ray standing wave microstructural characterization of NLO-active self-assembled chromophoric superlattices. J Am Chem Soc 119 2205-2211... 

Self assembly of non-centrosymmetric hybrid superlattices containing metal ions and unidirectionally aligned dipolar organic chromophores as intercalated... 

Figure 7. Plot of the square root of SHG intensity versus the number of chromophore layers in the multilayer superlattice. The straight lines are the linear least-squares fit to the experimental data. The number labels correspond to the interferogram maxima in Figure 6.

FIGURE 4.24 High-P chromophoric building blocks used in self-assembled superlattices. 

Chromophoric self-assembled multilayers. Organic superlattice approaches to thin-film nonlinear optical materials, J. Amer. Chem. Soc. 112 7389 (1990). 

Yitzchaik S, Marks TJ. 1996. Chromophoric self assembled superlattices. Acc Chem Res 29(4) 197 202. 

Li, D. Ratner, M.A. Marks, T.J. Zhang, C.Yang, J. Wong. G.K. Chromophoric self-assembled multilayers. Organic superlattice approaches to thin-film nonlinear optical materials. J. Am. Chem. Soc. 1990. 112 (20), 7389. 

Figure 9. Examples ofhigh-P chromophore building blocks for layer-by-layer formation of siloxane-based superlattices.

Examples of chromophores incorporated in these superlattices include stil-bazolium, azo-dyes and heterocycle based systems [38-42]. 

The assembly of these superlattices involved sequential deposition of a sylane coupling layer, a stilbazolium chromophore layer, and an octachlorotrisiloxane... 

Marks and co-workers have su ested a new organic superlattice approach for developing covalently linked self-assembled, chromophore-containing multilayer sys-tems. In this approach, self-assemblies of intrinsically acentric multilayers of high fip chromophores on inorganic oxide substrates are formed. These multilayers show excellent adhering properties and are insoluble in common organic... 

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