Conjugated Assembly of Viologens with Spin Manipulation

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Multi-step redox processes are reported in several it-conjugated assemblies of photoelectrochemically active pyridinium units, leading to function-integrated molecular assembly. The strategy has been set to strongly link each redox active unit and then to understand the correlated redox properties, (1) The arylene-linked viologen dimers showed four-step reduction processes in which mono-radical, triplet diradical, half and full quinoid structures are controlled photoelectrochemically. (2) The coordination assembly of bidentate pyridyl pyridinium ligands with paramagnetic metal ions exhibited photochemically tunable spin ordering through antiferromagnetic coupling of the intervening pyridyl radicals. (3) The d-π-dependent multi-step redox processes were demonstrated in various bis(pyridinio)-β-diketone metal complexes, together with their discotic columnar structures. The interaction path analysis giving a guideline for the coming molecular devices with electronic communication will be discussed. Interestingly, triplet ground state was confirmed in inter-ligand trans-configuration and intra-ligand configuration of two pyridinylradicals, while the inter-ligand cis-configuration was thermally excited triplet state, i.e., singlet biradical in the ground state. The electrochemical control of both geometric and electronic structures of the helical conjugated polymers will be also introduced by precisely fabricating pyridinium units in poly (arylisocyanide). Additionally, new modification of conducting polymers will be also introduced by anodic nucleophilic substitution of pyridine derivatives. Remarkable progress has been made in the study of well-designed coordination polymers to take the major place in supramolecular chemistry, which is providing various kinds of nano-structures, in several-to-decades nanometer scales, by self-assembly of small building blocks.