Symmetry‐Broken Intermolecular Charge Separation of Cationic Radicals

Abstract

AbstractA quadrupolar compoundPyr‐BAwith two pyrrole‐type nitrogen atoms doped externally was prepared in this work. In high contrast with other π ionic radicals, its cationic radicalPyr‐BA⋅+undergoes unusual symmetry‐broken charge separation (SB‐CS), generating the mixed valence complex ofPyr‐BA+1−q⋅⋅⋅Pyr‐BA+1+q, whereqis the degree of charge transfer. Variable‐temperature (VT) single‐crystal analysis, absorption and EPR experiments all confirmed that aggregation and lower temperature would help to facilitate this SB‐CS process. Gibbs energy calculations and gauge‐including magnetically induced current simulation both validate that, forPyr‐BA⋅+, SB‐CS behavior is more favorable than the conventional dimerization mode. To the best of our knowledge, this is the first study that shows solid single‐crystal evidence for spontaneous SB‐CS between identical ionic radicals. Such a unique phenomenon is of great significance both in terms of fundamental aspects and uncharted material science.