Strategy for Stimuli-Induced Spin Control Using a Liquescent Radical Cation

A liquescent salt based on an N-pentylphenothiazine radical cation (1•+·NTf2–) exhibited a unique crystal–crystal phase transition from a paramagnetic orange solid to a diamagnetic green solid induced by brief, weak, and pinpoint mechanostress. Electron spin resonance and electronic spectroscopies revealed that this unprecedented solid-state spin controllability was attributable to mechanostress-triggered sequential association of the highly mobile radical species occurring under neat conditions.