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 cyclometallated iridium(III) bipyridine-aldehyde complexes [Ir(N-C) ₂(bpy-CHO)] (PF ₆) (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 ( ³MLCT) (dπ(Ir)→π ^*(bpy-CHO)) character. For complex 6, the excited state is also mixed with substantial ( ³IL) (π→π ^*) (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. © 2004 Elsevier B.V. All rights reserved.