title: Triplet excited state in platinum-acetylide oligomers: triplet localization and effects of conformation.
abstract: An experimental and theoretical investigation was carried out on a series of platinum-acetylide oligomers of the general structure Ph-CC-[PtL2-CC-(1,4-Ph)-CC-]n-PtL2-CC-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 this work 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. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were carried out on several of the oligomers using the hybrid Becke's three-parameter functional with the B3LYP correlation functional and the SDD basis set. The combined experimental and theoretical results provide very clear evidence that the triplet excited state is localized on a chromophore consisting approximately of a single -[PtL2-CC-(1,4-Ph)-CC-PtL2]- repeat unit. DFT calculations indicate that in the ground state conformers that differ in the (rotational) orientation of the 1,4-phenylenes with respect to the plane defined by the PtL2(C)2 units (twisted = t and planar = p) are very close in energy (difference of <1 kcal.mol-1). By contrast, in the triplet excited state, the p conformer is 3 kcal.mol-1 lower in energy than the t conformer. The torsional geometry change in the triplet state is reflected in the low-temperature phosphorescence spectra of the short oligomers, where separate emission bands are seen from the t and p conformers.
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA.
authors.forename: Ksenija
authors.initials: K
authors.lastname: Glusac
authors.forename: M Erkan
authors.initials: ME
authors.lastname: Köse
authors.forename: Hui
authors.initials: H
authors.lastname: Jiang
authors.forename: Kirk S
authors.initials: KS
authors.lastname: Schanze
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D009944:Organoplatinum Compounds / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013696:Temperature
chemical_list: D000480:Alkynes; D009944:Organoplatinum Compounds; D010984:Platinum