Facile Synthesis of Luminescent Ir-Pt-Ir Trimetallic Complexes

A new class of luminescent, heterotrimetallic supramolecular constructs partnering two bis-cyclometalated iridium centers with a diimine platinum acetylide center is introduced. Whereas most supramolecular constructs featuring cyclometalated iridium involve elaborate bridging ligands and are prepared under forcing conditions with low to moderate yields, the three Ir-Pt-Ir complexes described here are prepared at room temperature from simple precursors and isolated in near-quantitative yields. ESI-MS, NMR spectroscopy, and diffusion ordered spectroscopy confirm the identity and homogeneity of the trimetallic products. In comparison with monometallic model complexes, analysis of UV/Vis absorption, steady-state photoluminescence and time-resolved emission reveals the impacts of supramolecular assembly on the photophysical properties. UV/Vis absorption and cyclic voltammetry suggest perturbation of some frontier orbital energies as a result of assembly, and the emission spectra and lifetimes reveal efficient excited-state energy transfer via a Dexter mechanism, and show that the site of luminescence (platinum or iridium) depends on the identity of the cyclometalating ligand bound to iridium.