A Stable Luminescent, Rapidly Crystallized and Acid Stimulus‐Responsive Organic Radical†

Comprehensive Summary In this study, we successfully designed and synthesized a pyridine‐modified tris(2,4,6‐trichlorophenyl)methyl radical ( PyTTM ). PyTTM exhibited notably rapid single‐crystal formation in acetone. Single‐crystal X‐ray analysis revealed that molecular planarity and multidimensional intermolecular non‐covalent interactions were key factors driving its fast crystallization. Compared to TTM , PyTTM showed significantly enhanced photostability. The introduction of the pyridine group endowed PyTTM with reversible acid–base responsiveness and excellent cycling stability. Furthermore, the triangular radical ligand was able to self‐assemble with temed‐Pd(NO 3 ) 2 into a one‐dimensional macrocyclic chain. This work offers a promising design strategy for novel luminescent radicals that combine high stability, rapid crystallization, and acid–base stimulus responsiveness.