Bulky Aryl Isocyanides and Secondary-Sphere Ag(I) Improve Blue Phosphorescence in Pt(II) Acetylide Complexes

In this work, we describe blue-phosphorescent platinum acetylide complexes of the formula <i>cis</i>-[Pt(CN-Ar)₂(C≡C-2-py)₂] (<b>3</b>-<b>5</b>), where C≡C-2-py is 2-pyridylacetylide and CN-Ar is an aryl isocyanide with progressively increasing steric bulk. Treatment of these complexes with silver(I) tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (AgBAr^F₄) results in chelation of the Ag(I) ion by the two 2-pyridylacetylide ligands. Photophysical studies in solution and PMMA films, recorded at different concentrations, generalize the previous observation that coordination of Ag(I) improves the radiative rate constant and photoluminescence quantum yield (Φ_PL), by more than 2-fold in each case, and demonstrate two key effects of the bulky aryl isocyanides. First, in the silver-free precursor complexes, the aryl isocyanide ligands bring about an enhancement in Φ_PL when compared to alkyl isocyanide ligands. Furthermore, in the silver-bound complexes, steric bulk on the aryl isocyanides is an important factor for inhibiting aggregation in film samples, preserving deep-blue phosphorescence and promoting a further increase in Φ_PL, maximizing at Φ_PL = 0.22 with the most sterically crowded isocyanide.