Iridium ppy

Iridium ppy - Published on Web Synthesis and...

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Synthesis and Characterization of Facial and Meridional Tris-cyclometalated Iridium(III) Complexes Arnold B. Tamayo, Bert D. Alleyne, Peter I. Djurovich, Sergey Lamansky, Irina Tsyba, Nam N. Ho, Robert Bau, and Mark E. Thompson* Contribution from the Department of Chemistry, Uni V ersity of Southern California, Los Angeles, California 90089-0744 Received February 6, 2003; E-mail: [email protected] Abstract: The synthesis, structures, electrochemistry, and photophysics of a series of facial ( fac ) and meridional ( mer ) tris-cyclometalated Ir(III) complexes are reported. The complexes have the general formula Ir( C N ) 3 [where is a monoanionic cyclometalating ligand; 2-phenylpyridyl ( ppy ), 2-( p -tolyl)pyridyl ( tpy ), 2-(4,6-difluorophenyl)pyridyl ( 46dfppy ), 1-phenylpyrazolyl ( ppz ), 1-(4,6-difluorophenyl)pyrazolyl ( 46dfppz ), or 1-(4-trifluoromethylphenyl)pyrazolyl ( tfmppz )]. Reaction of the dichloro-bridged dimers [( ) 2 Ir( μ -Cl) 2 Ir- ( ) 2 ] with 2 equiv of H at 140 - 150 ° C forms the corresponding meridional isomer, while higher reaction temperatures give predominantly the facial isomer. Both facial and meridional isomers can be obtained in good yield ( > 70%). The meridional isomer of Ir( ) 3 and facial and meridional isomers of Ir( ) 3 and Ir( ) 3 have been structurally characterized using X-ray crystallography. The facial isomers have near identical bond lengths (av Ir - C ) 2.018 Å, av Ir - N ) 2.123 Å) and angles. The three meridional isomers have the expected bond length alternations for the differing trans influences of phenyl and pyridyl/ pyrazolyl ligands. Bonds that are trans to phenyl groups are longer (Ir - Cav ) 2.071 Å, Ir - Nav ) 2.031 Å) than when they are trans to heterocyclic groups. The Ir - C and Ir - N bonds with trans N and C, respectively, have bond lengths very similar to those observed for the corresponding facial isomers. DFT calculations of both the singlet (ground) and the triplet states of the compounds suggest that the HOMO levels are a mixture of Ir and ligand orbitals, while the LUMO is predominantly ligand-based. All of the complexes show reversible oxidation between 0.3 and 0.8 V, versus Fc/Fc + . The meridional isomers are easier to oxidize by ca. 50 - 100 mV. The phenylpyridyl-based complexes have reduction potentials between - 2.5 and - 2.8 V, whereas the phenylpyrazolyl-based complexes exhibit no reduction up to the solvent limit of - 3.0 V. All of the compounds have intense absorption bands in the UV region assigned into 1 ( π f π *) transitions and weaker MLCT (metal-to-ligand charge transfer) transitions that extend to the visible region. The MLCT transitions of the pyrazolyl-based complexes are hypsochromically shifted relative to those of the pyridyl-based compounds. The phenylpyridyl-based Ir(III) tris-cyclometalates exhibit intense emission both at room temperature and at 77 K, whereas the phenylpyrazolyl-based derivatives emit strongly only at 77 K. The emission energies and lifetimes of the phenylpyridyl-based complexes (450 - 550 nm, 2 - 6 μ s) and phenylpyrazolyl-based compounds (390 - 440 nm, 14 - 33 μ s) are characteristic for a mixed ligand-centered/MLCT excited state. The meridional isomers for both pyridyl and pyrazolyl-based
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This note was uploaded on 03/27/2011 for the course CHEM 2211L taught by Professor T.a. during the Spring '08 term at UGA.

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Iridium ppy - Published on Web Synthesis and...

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