Do Anionic π Molecules Aggregate in Solution? A Case Study with Multi‐interactive Ligands and Network Formation

An anionic π molecule can form an aggregate when a multi‐interactivity is introduced, in sharp contrast to common anionic molecules that are generally difficult to stack on each other. We found that a multi‐interactive ligand, 2,5,8‐tri(4′‐pyridyl)‐1,3,4,6,7,9‐hexaazaphenalenate (TPHAP−) exhibited a large Stokes shift and an intramolecular charge transfer, both of which were sensitive to hydrogen‐bonding media. An anionic potassium salt of TPHAP− in methanol formed various aggregation states depending on the concentration examined; this was revealed by steady‐state spectroscopic and fluorescence lifetime measurements. Self‐assembling cadmium ions and the ligands can create several morphological crystals that are controlled by the ligand concentration, among which three new structures were determined by single‐crystal analysis. The X‐ray structures obtained suggest that the aggregation states of the ligand in solution can be transferred to the solid system of the porous coordination networks. Crossing the solvent–solid divide: Anionic π molecules aggregate when multiple interactions are introduced. A multi‐interactive ligand, TPHAP−, formed various aggregation states depending on the concentration. Self‐assembling cadmium ions and the ligands can create several morphological crystals that are controlled by the ligand concentration, suggesting that the aggregation states of the ligand in solution can be transferred to the solid system.