Ferroelectric LC Polymeric Systems

Since the early days of ferroelectric low molar mass LC research, the exploration of the NLO properties of these substances has been a topic of interest. For a recent review on SHG in ferroelectric LCs, see [215]. Unfortunately, the SHG efficiency of most ferroelectric LCs investigated so far [216-219] is orders of magnitude below that of state-of-the-art inorganic crystals, such as lithium niobate. The main reason for the low electronic NLO activity is that the ferroelectric LC compounds and mixtures used in these investigations were optimized for display applications rather than for NLO performance. Quite recently, some research groups started the development of ferroelectric LC compounds specifically devoted to NLO applications, and indeed improved the SHG efficiency by orders of magnitude [220-224]. 

As already mentioned, NLO chromo-phores with large values normally consist of a donor and an acceptor group which are 

IV Behavior and Properties of Side Group Thermotropic Liquid Crystal Polymers 

On the basis of this design approach, Wal-baet al. [222] succeeded in synthesizing the (o-nitroalkoxy)phenyl biphenylcarboxylate 47 exhibiting a d22=d2 value of 0.6 pmA (t/eff=0.23 pm/V). 

Quite recently, Schmitt et al. [223] presented highly efficient NLO ferroelectric LC materials (48) whose SHG properties were investigated in 13 pm thin, homeo-tropically aligned layers. 

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