Symmetry-Broken Intermolecular Charge Separation of Cationic Radicals

Authors：Liu, Guanghua; Gao, Lei; Han, Yi; Xiao, Yao; Du, Bochao; Gong, Jianye; Hu, Jinlian; Zhang, Fujin; Meng, He; Li, Xiang; Shi, Xueliang; Sun, Zhe; Wang, Jianguo; Dai, Gaole^*; Chi, Chunyan^*; Wang, Qing^*

Source：Angewandte Chemie - International Edition, 2023, 62(15): e202301348.

DOI：10.1002/anie.202301348

• Cationic Radical
• Mixed Valence Complex
• Nitrogen Doping
• Quadrupole
• Symmetry Broken Charge Separation

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

• Institution
  天津大学; 杭州师范大学; 南京农业大学