Pressure-Induced Conductivity in a Neutral Nonplanar Spin-Localized Radical

There
is a growing interest in the development of single-component molecular
conductors based on neutral organic radicals that are mainly formed
by delocalized planar radicals, such as phenalenyl or thiazolyl radicals.
However, there are no examples of systems based on nonplanar and spin-localized
C-centered radicals exhibiting electrical conductivity due to their
large Coulomb energy (U) repulsion and narrow electronic
bandwidth (W) that give rise to a Mott insulator
behavior. Here we present a new type of nonplanar neutral radical
conductor attained by linking a tetrathiafulvalene (TTF) donor unit
to a neutral polychlorotriphenylmethyl radical (PTM) with the important
feature that the TTF unit enhances the overlap between the radical
molecules as a consequence of short intermolecular S···S
interactions. This system becomes semiconducting upon the application
of high pressure thanks to increased electronic bandwidth and charge
reorganization opening the way to develop a new family of neutral
radical conductors.