Aggregation Game: Changing Solid-State Emission Using Different Counterions in Monoalkynylphosphonium Pt(II) Complexes

Two series of heteroleptic monoalkynylphosphonium Pt(II) complexes decorated with 2,2':6',2''-terpyridine (<b>terpy</b>, <b>N</b> series) and 6-phenyl-2,2'-bipyridine (<b>phbpy</b>, <b>C</b> series) ligands, were prepared and characterized by spectroscopic methods. The complexes obtained exhibit triplet emission in solution, and the characteristics inside the series depend on the nature of the alkynylphosphonium ligand. The description of electronic transitions responsible for energy absorption and emission in discrete Pt(II) complexes was made on the basis of a detailed analysis of the results of DFT calculations, and has shown to involve MLCT, ILCT, and LLCT transitions. The complexes of both series exhibit triplet solid-state luminescence with parameters that also depend on the composition of the complexes, and the analysis of the experimental data indicates the realization of LC, MLCT, MMLCT, and MC transitions due to Pt⋯Pt metallophilic interactions and matrix rigidity. It was shown that the anion variation leads to a significant difference in the photophysical characteristics of the <b>N</b> complexes, which exhibit a smooth dependence of the luminescent properties on the anion size. Using quantum chemical modeling, it is demonstrated how the anion size influences the Pt⋯Pt distance in the solid state.