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)](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 (3MLCT) (dπ(Ir) → (bpy–CHO)) character. For complex 6, the excited state is also mixed with substantial (3IL) () (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.