Nonlinear optics, molecular layers possibilities

Both quantum functional materials and molecular devices are considered to be the ultimate functional materials. The former shows a novel property which is specific to the structure and the latter represents the smallest possible functional material. Their properties are closely related to optical and photonic functions. The former shows a quantum size effect, a photoluminescence shift to higher energy which depends on layer thickness, which gives us an idea of a nonlinear optical system. Porphyrin arrays connected with molecular wires show a hole carrier photoconductivity or a photoswitching and a photo-information storage, which suggests an idea of a photoactive neuron model. In this paper, conjugated polymer superlattices and porphyrin arrays connected with molecular wires are described. 

In the field of the synthesis of molecule-based second order nonlinear optical materials, the self assembly approach has attracted much attention in recent years because it leads to obtain functional and structurally stable molecular films, as a consequence of the intrinsic versatility of molecular chemistry and mild deposition conditions possible [75, 137, 138], Although the most detailed investigations of self-assembly have focused on long chain alkanethiol and alkyl-silane derivatives, the potential for formation of relatively ordered, densely packed arrays of electronically functional molecules is of great scientific interest the chance to modify surfaces with self-assembled layers terminated with reactive... 

In short, these papers demonstrate significant accomplishment and the viability of organic thin-film devices for nonlinear optics. They also demonstrate the possibility to tune the features of an organic molecule and establish new functions within a molecular assembly. Such devices exploit the control of the internal layer architecture on a molecularly defined level. However, despite these remarkable accomplishments the strong competition of other approaches has to be considered as well, and these alternative approaches may eventually be commercially successful. Discussions and a realistic judgement of the potential of the LB technique in this context cannot ignore the tremendous progress... 

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