Synthesis, characterization, and luminescence of platinum(II) polypyridines

Michael H Wilson, Purdue University


In recent years there has been considerable interest in platinum(II) complexes of 2,2′:6′,2′ ′-terpyridine and derivatives thereof because of the emission properties and DNA bonding interactions. However, chloro(2,2 ′:6′,2′′ -terpyridine)platinum(II) is non-luminescent in fluid solution. This is believed to be the result of a thermally accessible deactivating d-d excited state. By altering the terpyridine ligand the energy and orbital parentage of the lowest energy excited state can be changed to slow radiationless decay. For example, when a phenyl ring is fused into the terpyridine backbone to give 2-(2′-pyridyl)-1,10-phenanthroline, the complex becomes emissive with a lifetime of 230 ns in solution. This work presents several new approaches to improve the luminescent properties of platinum(II) polypyridines. In the first approach we replace the halide ligand with the π-acceptor cyanide ligand. The idea is that a π-acceptor ligand will drive up the energy of the d-d deactivating state and enhance the luminescence properties of the complex. In a second approach, we enlarged the N-Pt-N bite angle with 2-(8′-quinolyl)-1,10-phenanthroline. The increased bite angle should allow for stronger orbital overlap and drive the d-d deactivating state to higher energy. The third approach involves introducing a carbon-metal bond into the complex. Two different types of carbometalated complexes, a series of cyclometalated complexes using 2-phenyl-1,10-phenanthroline and a series of polypyridine complexes with an acetylide co-ligand, propargyl alcohol, are studied. Each of these approaches address the same basic problem and are aimed at increasing the barrier to thermal deactivation. If the barrier can be made high enough, the lifetime of the excited states and the large quantum will increase and enhance the utility.




McMillin, Purdue University.

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