Development of Stable Neutral Radicals Having an Unconventional Spin-Delocalized Nature

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Organic open-shell molecules, widely recognized as short-lived reactive intermediates, have recently drawn attention as building blocks for new molecule-based functional materials, since various stabilization techniques have been developed. In order to strengthen the basis of this research field, it is crucial to establish novel design criteria and synthetic methodologies of open-shell molecular systems with structurally and electronically salient features. In this study, we have synthesized and characterized new organic open-shell systems having topologically-controlled and extremely delocalized spin-density distribution natures, demonstrating exotic electronic features originating from these electronic spin structures. (1) realization of novel thermochromism based on dynamic electron-spin behavior : We have experimentally determined chemical structure of Ti-dimer formed in a solution state at low temperature, revealing a new C-C bond with 12-center-2-electron nature. Furthermore, aromaticity of a radical aggregate was first proposed in our study. (2) realization of the switching system in terms of spin-center transfer of purely organic open-shell system : We have prepared TTF-linked 6-oxophenalenoxyl neutral radical system, and created solvent-and temperature-controlled complete spin-switching system based on intramolecular electron transfer. (3) The delocalized singlet biradical hydrocarbons were first synthesized, isolated, and characterized, showing the highest room-temperature electric conductivity as single-component hydrocarbon, and exceptionally large two-photon absorption cross sections for pure hydrocarbon with no electron-donor or-acceptor substituents.