Asymmetry in Platinum Acetylide Complexes: Confinement of the Triplet Exciton to the Lowest Energy Ligand (Preprint)

摘要

As part of an ongoing investigation of structure-optical property relationships in platinum acetylide complexes, we synthesized the compounds trans-Pt(PBU3)2(C=CC6HS) (C=C-C6H4-C=CC6HS)(PE 1-2), trans-Pt(PBU3h)(C=CC6HS)(C=CC6H4- C=C-C6 approximately-C=CC6Hs)(PEl-3) and trans-Pt(PBU3h)(C=C-C6 approximately- C=CC6Hs)(C=CC6H4-C=C- C6H4-C=CC6Hs)(PE2-3)that have different ligands on either side of the central platinum and compared their spectroscopic properties to the symmetrical compounds PE1, PE2 and PE3. We measured trends in ground state absorption, fluorescence, phosphorescence and triplet state absorption spectra. We also performed density functional theory calculations of the triplet state geometries and energies. The ground state absorption and fluorescence spectra give evidence the singlet exciton is delocalized across the central platinum atom. In contrast, the behavior of the phosphorescence spectra suggests the triplet excitonis confined to one ligand. The phosphorescence from the asymmetric complexes comes from the lowest energy, most delocalized ligand. The triplet state geometries obtained from the density functional theory calculations show distortion on the lowest energy ligand, while the other ligand has the ground state geometry. The calculated trend in the triplet state energies agrees very well with the experimental trend. Calculations of triplet state spin density also show the triplet excitonis confined to one ligand. In the asymmetric complexes the spin density is confined to the more conjugated, lower energy ligand. The results show Kasha's rule applies to these complexes, where following excitationand intersystem crossing, the triplet exciton moves to the lowest energyligand.