| Abstract
| - An experimental and theoretical investigation was carried out on a series of platinum−acetylide oligomers ofthe general structure Ph−C⋮C−[PtL2−C⋮C−(1,4-Ph)−C⋮C−]n−PtL2−C⋮C−Ph (where n = 1, 2, 3, 4, 6;Ph = phenyl, 1,4-Ph = 1,4-phenylene; L = P(n−Bu)3, and the geometry at Pt = trans). The objective of thiswork is to understand the geometry and electronic structure of the ground and triplet excited states of Pt−acetylide oligomers. The experiments carried out include temperature-dependent absorption and photoluminescence spectroscopy (80−298 K range) and ambient temperature transient absorption spectroscopy. Densityfunctional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were carriedout on several of the oligomers using the hybrid Becke's three-parameter functional with the B3LYP correlationfunctional and the SDD basis set. The combined experimental and theoretical results provide very clear evidencethat the triplet excited state is localized on a chromophore consisting approximately of a single −[PtL2−C⋮C−(1,4-Ph)−C⋮C−PtL2]− repeat unit. DFT calculations indicate that in the ground state conformers thatdiffer in the (rotational) orientation of the 1,4-phenylenes with respect to the plane defined by the PtL2(C)2units (twisted = t and planar = p) are very close in energy (difference of <1 kcal·mol-1). By contrast, in thetriplet excited state, the p conformer is 3 kcal·mol-1 lower in energy than the t conformer. The torsionalgeometry change in the triplet state is reflected in the low-temperature phosphorescence spectra of the shortoligomers, where separate emission bands are seen from the t and p conformers.
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