Functional Coordination Polymers That Self-assemble in Solution

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By converting pseudo-one-dimensional metal complexes to amphiphilic nanowire structures, a new research field of coordination polymers with strongly correlated electron systems has emerged, which allows control of electronic and spin states based on reversible self-assembly in solution. Lipid-packaged one-dimensional complexes have been obtained by introducing lipid counterions to ionic, halogen-bridged, mixed-valence complexes. They become soluble in organic media and can be dispersed as nanowires, with the electronic structures significantly controlled depending on the lipid molecular structures. In addition, spin conversion phenomena were first observed by thermally controlled self-assembly of Fe(ii) 1,2,4-triazole complexes in organic media. Lipophilic bridging ligands such as N-alkylated 1,2,4-triazoles also afford lipophilic coordination polymers, and those of Co(ii) complexes showed the first example of heat-set organogel formation. The electrophoretic orientation of halogen-bridged diruthenium mixed-valence complexes allowed controlled macroscopic orientation of the coordination main chain in response to an applied electric field. The covalent introduction of triplet sensitizers and emitters to lipophilic one-dimensional complexes also leads to triplet energy migration-based photon upconversion properties. The design of lipophilic coordination polymers has led to a new family of self-assembling functional materials with unique functionalities unavailable in conventional solid-state coordination chemistry.