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Recent Advances in Second Order Nonlinear Optical Polymers with Dendritic Structure

Zhong-an Li;Zhen Li;Department of Chemistry,Wuhan University;  
Dendritic molecules are a class of highly branched macromolecules and/or polymers having a three-dimensional, nanosized globular architecture with intramolecular cavity and numerous surface functional groups. These unique structural features can endow dendritic molecules with a lot of particular and interesting functionalities and photophysical properties, making them very attractive in many areas including chemistry, biology, materials, and so on. In the past 30 years, organic/polymeric second-order nonlinear optical(NLO) materials have been widely investigated due to their great potential in telecommunications, computing, terahertz generation, detection, and many other photonic applications. So far, one of the major challenges encountered in this field is how to translate high molecular nonlinearities(μβ) of chromophores into large macroscopic material nonlinearities(i.e. second harmonic generation coefficient, d33) efficiently, due to the strong intermolecular dipole-dipole interactions between chromophore moieties, which can make their poling induced noncentrosymmetric alignment a daunting task. According to the site-isolation principle, the dendritic structure has been well-recognized as the next generation molecular topology to modify chromophores into the ideal spherical shape that can minimize the dipole-dipole interactions significantly to improve the poling efficiency. From 2006, our group has done many systematic researches in this field with an attempt to better understand the structure-properties relationship of NLO polymeric materials. In this review, after a brief introduction of dendritic molecules and second order nonlinear optics, we will summarize our recent research work on second order NLO polymers with dendritic structure, including high generation dendrimers, hyperbranched polymers and dendronized hyperbranched polymers(a new polymer model combining hyperbranched polymer and dendrimer). We mainly focus on the discussion how to rationally design and tailor the topological structures of the dendritic NLO polymers that can significantly enhance their comprehensive material performance through several molecular design strategies such as "suitable isolation group", "isolation chromophore" and the Ar-ArFself-assembly. Finally, a short outlook for future opportunities in advancing this field is also presented.
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