Self-assembly of thin film superstructures based on alternating metal-bisphosphonate and cobalt-diisocyanide layers

A new chemical strategy for the synthesis of self-assembled (SA) multilayer superstructures is described which allows facile incorporation of aligned nonlinear optical (NLO) chromophores. This strategy involves alternating layers of the well-established metal-bisphosphonate system with layers of the recently reported cobalt-diisocyanide SA system. Previously, building SA multilayers with oriented NLO chromophores has required extra activation or deprotection steps that are time consuming and which often involve harsh chemical treatments. Several results showing the feasiblity of the new approach are presented. A film incorporating the desired chemistries was synthesized and characterized by ellipsometry. Control experiments demonstrating the necessary metal-ligand binding specificity (cobalt with isocyanide versus hafnium with phosphonate ligands) are reported. Cobalt-diisocyanohexane films exhibiting alkyl-isocyanide-cobalt linkages are reported for the first time, including characterization by ellipsometry and grazing angle X-ray diffraction. Thus, both alkyl- and aryl-isocyanide functionalities in cobalt-isocyanide multilayers have now been shown to be feasible components of the proposed supramolecular structures. Finally, preliminary second harmonic generation data are presented, demonstrating the potential utility of the materials.