Chromium-containing organometallic nanomaterials for non-linear optics

Abstract

Novel non-linear optical polymeric film-producing nanocomposites based on bis(arene)chromium complexes incorporated into a CN-containing matrix have been developed. Polymeric nanocomposite precursors were prepared by the reaction of Cr(Et_nC₆H_6−n)₂ (n = 1,2,3) with CN-containing vinyl monomers (acrylonitrile, crotononitrile or ethyl 2-cyanopropenoate). Extraordinarily high third-order non-linear optical susceptibilities of the ultra-fast electronic type have been demonstrated at various wavelengths for polymer films prepared from these composites by using the Z-scan technique and the spectrally-resolved two-beam coupling method. A notable electro-optical response of the composite with an essential contribution of orientational effects was established. The electron-diffraction pattern in films and the presence of a non-zero electro-optical coefficient in the absence of an external poling field indicate the formation of self-organized structures. In CrPAN and [CrPAN]⁺TCNE⁻, a single Cr–C distance was found in the EXAFS data refinement, showing that the arene rings are parallel and symmetric as in bis(benzene)chromium. The Cr–C distances in these two materials are very similar to the 2.13 Å in bis(benzene)chromium. In [CrPAN]⁺OH⁻, more than one metal–carbon distance was resolved, showing either that the two arene rings are at different distances from the metal, or that they are tilted rather than parallel.