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Photophysical Properties of Near-Infrared Phosphorescent π-Extended Platinum Porphyrins

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journal contribution
posted on 27.12.2011 by Jonathan R. Sommer, Abigail H. Shelton, Anand Parthasarathy, Ion Ghiviriga, John R. Reynolds, Kirk S. Schanze
A comprehensive photophysical study is reported on a family of π-extended platinum­(II) porphyrin complexes. The platinum­(II) complexes are synthesized from the corresponding free base porphyrins by treatment with platinum­(II) acetate in hot benzonitrile, affording the complexes in considerably higher yield than by reaction with platinum­(II) chloride. A quantitative study of the absorption and luminescence properties of the metalloporphyrins is presented. A series including tetraarylbenzo-, tetraarylnaphtho-, and tetraarylanthroporphyrin exhibits efficient phosphorescence at 773, 890, and 1020 nm in the near-infrared region, with quantum yields of 0.35, 0.15, and 0.08, respectively. The triplet lifetimes and phosphorescence yields decrease with increasing emission wavelength, consistent with energy gap law behavior. A set of six Pt-tetrabenzoporphyrins (TBPs) with different meso-substituents were examined. The Pt-TBPs exhibit efficient phosphorescence with λmax ∼ 770 nm and with a quantum yield ranging from 0.26–0.49, depending on the substitution pattern. The results show that the 5,15-diarylbenzoporphyrins feature 50–60% higher phosphorescence emission yield compared to the 5,10,15,20-tetraarylbenzoporphyrins. The highest phosphorescence quantum efficiency is observed for a platinum­(II) 5,15-diarylbenzoporphyin which emits at 770 nm with a quantum yield of 49%.