Symmetry‐Broken Intermolecular Charge Separation of Cationic Radicals

Abstract

A quadrupolar compound Pyr‐BA with two pyrrole‐type nitrogen atoms doped externally was prepared in this work. In high contrast with other π ionic radicals, its cationic radical Pyr‐BA⋅+ undergoes unusual symmetry‐broken charge separation (SB‐CS), generating the mixed valence complex of Pyr‐BA+1−q⋅⋅⋅Pyr‐BA+1+q, where q is 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, for Pyr‐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.

NHC-catalyzed enantioselective radical reactions of enal and pyridinium salt: mechanism and origin of regio- and stereoselectivities

“…Radical reactions have become increasingly popular due to their numerous advantages, such as relatively mild reaction conditions, excellent functional group tolerance, and the ability to efficiently and quickly assemble complex molecules and functions. [1][2][3] As a result, these kinds of reactions have been widely applied across various fields, including organic synthesis, 4,5 drug design, [6][7][8] materials science, [9][10][11] and more. In recent years, a variety of effective radical generation strategies and highly selective radical reactions have been developed using photochemistry, [12][13][14] electrochemistry, [15][16][17] organic superelectron donors, 18,19 and transition metal catalysis.…”