| Abstract
| - The synthesis, electrochemistry, and photophysics of a series of square planar Pt(II) complexes are reported. Thecomplexes have the general structure C∧NPt(O∧O),where C∧N is a monoanionic cyclometalating ligand (e.g.,2-phenylpyridyl, 2-(2‘-thienyl)pyridyl, 2-(4,6-difluorophenyl)pyridyl, etc.) and O∧O is a β-diketonato ligand. Reactionof K2PtCl4 with a HC∧N ligand precursor forms the chloride-bridged dimer, C∧NPt(μ-Cl)2PtC∧N, which is cleavedwith β-diketones such as acetyl acetone (acacH) and dipivaloylmethane (dpmH) to give the corresponding monomericC∧NPt(O∧O) complex. The thpyPt(dpm) (thpy = 2-(2‘-thienyl)pyridyl) complex has been characterized using X-raycrystallography. The bond lengths and angles for this complex are similar to those of related cyclometalated Ptcomplexes. There are two independent molecular dimers in the asymmetric unit, with intermolecular spacings of3.45 and 3.56 Å, consistent with moderate π−π interactions and no evident Pt−Pt interactions. Most of the C∧NPt(O∧O) complexes display a single reversible reduction wave between −1.9 and −2.6 V (vs Cp2Fe/Cp2Fe+), assignedto largely C∧N ligand based reduction, and an irreversible oxidation, assigned to predominantly Pt based oxidation.DFT calculations were carried out on both the ground (singlet) and excited (triplet) states of these complexes. TheHOMO levels are a mixture of Pt and ligand orbitals, while the LUMO is predominantly C∧N ligand based. Theemission characteristics of these complexes are governed by the nature of the organometallic cyclometalatingligand allowing the emission to be tuned throughout the visible spectrum. Twenty-three different C∧N ligands havebeen examined, which gave emission λmax values ranging from 456 to 600 nm. Well-resolved vibronic fine structureis observed in all of the emission spectra (room temperature and 77 K). Strong spin−orbit coupling of the platinumatom allows for the formally forbidden mixing of the 1MLCT with the 3MCLT and 3π−π* states. This mixing leadsto high emission quantum efficiencies (0.02−0.25) and lifetimes on the order of microseconds for the platinumcomplexes.
- A series of cyclometalated platinum complexes of the general structure C∧NPtO∧O, where C∧N is a cyclometalated ligand (e.g., 2-phenylpyridine) and O∧O is a β-diketonato ligand (e.g., acetyl acetonate) are presented. These compounds emit from a mixed 3LC/MLCT state which is governed by the nature of the cyclometalating ligand. The photophysics and electrochemistry are discussed.
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