Multistimuli‐Responsive Chromic Properties of Soft Salts Based on Cyclometalated Platinum(II) Complexes: Pyridine‐ vs. Pyrimidine‐Based Ligands

We report the synthesis and characterization of four luminescent soft salts ( S1–S4 ), composed of ion‐paired cyclometalated Pt(II) complexes featuring either pyridine‐ or pyrimidine‐based ligands. These compounds were prepared via metathesis reactions between complementary cationic and anionic Pt(II) precursors and were fully characterized by NMR spectroscopy and electrospray ionization high‐resolution mass spectrometry. Their photophysical and chromic properties were investigated, and their excited states were modeled using time‐dependent density functional theory. In DMSO solution, the emission originates from the anionic fragment, with quantum yields reaching up to 0.69. In the solid state, a redshifted emission is observed, attributed to metal–metal‐to‐ligand charge transfer excited states formed between paired complexes. Soft salts bearing a pyrimidine‐based anionic fragment exhibit aggregation‐induced emission, whereas their pyridine‐based analogs show aggregation‐caused quenching in DMSO/water mixtures. Soft salts incorporating pyrimidine‐based ligands display vapochromic and acid‐responsive behavior, with emission shifts or quenching upon exposure to solvent or acid vapors; partial reversibility is achieved through grinding or treatment with ammonia. These results underscore the tunability of photophysical properties through strategic azaheterocyclic ligand design and aggregation control.