Loading…

Structure−Optical Property Relationships in Organometallic Sydnones

As part of an effort to develop a spectroscopic structure−property relationship in platinum acetylide oligomers, we have prepared a series of mesoionic bidentate Pt(PBu3)2L2 compounds containing sydnone groups. The ligand is the series o-Syd-(C6H4−C⋮C) n -H, where n = 1−3, designated as Syd-PEn-H. T...

Full description

Saved in:
Bibliographic Details
Published in:The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2005-02, Vol.109 (6), p.999-1007
Main Authors: Cooper, Thomas M, Hall, Benjamin C, McLean, Daniel G, Rogers, Joy E, Burke, Aaron R, Turnbull, Kenneth, Weisner, Andrew, Fratini, Albert, Liu, Yao, Schanze, Kirk S
Format: Article
Language:English
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:As part of an effort to develop a spectroscopic structure−property relationship in platinum acetylide oligomers, we have prepared a series of mesoionic bidentate Pt(PBu3)2L2 compounds containing sydnone groups. The ligand is the series o-Syd-(C6H4−C⋮C) n -H, where n = 1−3, designated as Syd-PEn-H. The terminal oligomer unit consists of a sydnone group ortho to the acetylene carbon. We synthesized the platinum complex (Syd-PEn-Pt), the unmodified ligands (PEn-H), and the unmodified platinum complexes (PEn-Pt). The compounds were characterized by various methods, including X-ray diffraction, 13C NMR, ground-state absorption, fluorescence, phosphorescence, and laser flash photolysis. From solving the structure of Syd-PE1-Pt, we find the angle between the sydnone group and the phenyl group is 45°. By comparison of the 13C NMR spectra of the sydnone-containing ligands, the sydnone complexes with the corresponding unmodified ligands and complexes not containing the sydnone group, the sydnone group is shown to polarize the nearest acetylenes and have a charge-transfer interaction with the platinum center. Ground-state absorption spectra of the complexes in various solvents give evidence that the Syd-PE1-Pt complex has an excited state less polar than the ground state, while the PE1-Pt complex has an excited state more polar than the ground state. In all the higher complexes the excited state is more polar than the ground state. The phosphorescence spectrum of the Syd-PE1-Pt complex has an intense vibronic progression distinctly different from the PE1-Pt complex. The sydnone effect is small in Syd-PE2-Pt and negligible in Syd-PE3-Pt. From absorption and emission spectra, we measured the singlet-state energy E S, the triplet-state energy E T, and the singlet−triplet splitting ΔE ST. By comparison with energies obtained from the unmodified complexes, attachment of the sydnone lowers E S by ∼0.1 eV and raises E T by ∼0.1 eV. As a result, the sydnone group lowers ΔE ST by ∼0.2 eV. The trends suggest one of the triplet-state singly occupied molecular orbitals (SOMOs) is localized on the sydnone group, while the other SOMO resides on the rest of the ligand.
ISSN:1089-5639
1520-5215
DOI:10.1021/jp046806t