Cyclometallated platinum and palladium complexes with N^C^N-coordinating terdentate ligands : synthesis, luminescence and catalytic properties

• Main Author: Rochester, David Lee
• Published: Durham University 2007
• Subjects: 541.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486174

A series of cyclometallated platinum and palladium(lI) complexes based on the N'C'N coordinating terdentate ligand 1,3-di(2-pyridyl)benzene, HL1, have shown that cyclometalation at C2 of the central ring affords many advantages to square-planar d8-metal complexes. The cyclometalating bond is notably shorter than that observed in many related cyclometallated complexes, e.g. 6phenyl- 2,2'-bipyridine platinum/palladium(lI) chloride and 2-phenylpyridine derivatives. The luminescent properties of the complexes reported herein have been investigated. All complexes are intensely luminescent, in their own right, with quantum yields of luminescence significantly higher than those reported for :related complexes. In the solid-state and at high concentrations, intermolecular interactions create new emissive species, such as self-quenching accompanied 'by excimeric emission observed in solution, Aem =: 700 nm, and multi-centred excited-states in solid samples, Aem =610-700 nm. Modification of both N'C'N and ancillary ligands is shown to manipulate the electronic properties of the d8 _ . metal complexes. Excited-state emission energies have been tuned from 469 nm (blue), L26ptCI, to 588 nm (red), L16ptCI, in the platinum(lI) complexes, and from 466 nm (blue), L1pdCI, to 530 nm (orange), L16pdCI, in the palladium comp!exes. Incorporation of steric incumberance into the ligands can attenuate the excimer emission compared to L1PtCI. Electron-rich pendant ligands encourage the accessibility of charge-transfer excited-states, which adds to the diversity of the photophysical properties, but when coupled with functional groups can give rise to potential in sensory applications. The high quantum yields and special oxygen sensitivity of the platinum complexes have allowed their incorporation into optoelectronic devices. The palladium complexes are of particular interest owing to the limited attention previously paid to palladium complexes as emissive species, particularly, excimeric behaviour is even rarer. Additionally, the electronic tuning which is manifested in the luminescent properties of these complexes has allowed studies into catalytic behaviour of these complexes, revealing some surprising results relating activity to structure.