Exploration of Molecular Materials based on Cooperative Proton-Electron Systems

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Search for new molecular materials based on the cooperative interactions between proton and electron has been performed. We developed a general strategy to explore new molecular materials. Cooperative proton-electron transfer (PET) in the hydrogen-bonded charge transfer (HBCT) systems might produce a molecular assembly of H-bonded neutral redicals. The solid state properties of such PET systems depend on the type and strength of the proton-electron cooperativity. A molecular level consideration leads to two reasonable molecular design strategies : the exploration of new electronic systems having smaller intermolecular CT gap and an electronic modification to stabilize H-bonded neutral radical state. According to the strategies, we synthesized new PET systems : (1) the donor and acceptor substituted quinhydrones, (2) the extended conjugated quinhydrones, and (3) the transition metal complexes having H-bonding networks. For example, as for the approach (1), we modified the prototype benzoquinhydrone by introducing the electron donor and the acceptor substituents. As for (2), we synthesized naphtho-, bipheno-, and stilben-quinhydrone as extended conjugated quinhydrones. In these quinhydrones, we have found cooperative phenomena between H-bonding and CT interaction. In order to expand the PET systems, new approach (3) are now actively performed. In the H-bonded transition metal complexes, we can utilize the additional characteristics of redox properties of the metal atoms and the intermolecular interactions between the metal atoms or between the metal atom and the ligand. As a first step, we succeeded to construct a H-bonded dimer model of the biimidazole transition metal complex. We are now concentrated to construct new H-bonded molecular systems of biimidazole-type and pteridine-type transition metal complexs.