Synthesis, photophysical and electrochemical properties, and biological labelling studies of luminescent cyclometallated iridium(III) bipyridine-aldehyde complexes

We report the synthesis, characterisation, and photophysical and electrochemical properties of a series of luminescent cyclo-metallated iridium(III) bipyridine-aldehyde complexes [Ir(N-C)(2)(bpy-CHO)](PF6) (HN-C = 2-phenylpyridine, Hppy (1); 2-(4-methylphenyl)pyridine, Hmppy (2); 1-phenylpyrazole, Hppz (3); 3-methyl-1-phenylpyrazole, Hmppz (4); 7,8-benzoquinoline, Hbzq (5); 2-phenylquinoline, Hpq (6); bpy-CHO = 4-formyl-4-methyl-2,2'-bipyridine). The X-ray crystal structures of complexes 1 and 4 have been determined. On the basis of the photophysical data, the emission of these complexes is assigned to an excited state of predominantly triplet metal-to-ligand charge-transfer ((MLCT)-M-3) (dpi(Ir) --> pi*(bpy-CHO)) character. For complex 6, the excited state is also mixed with substantial ((IL)-I-3) (pi --> pi*) (pq(-)) character. The protein bovine serum albumin has been labelled with these complexes to produce luminescent bioconjugates. The photophysical properties of the luminescent conjugates have also been investigated. (C) 2004 Elsevier B.V. All rights reserved.