SYNTHESIS AND CHARACTERIZATION OF 2 RUTHENIUM(II) HETEROLEPTIC COMPLEXES OF ANNELATED DERIVATIVES OF 2,2'-BIPYRIDINE

The synthesis and characterization of two annelated 2,2'-bipyridine mo lecules (L) and of the corresponding ruthenium(II) heteroleptic comple xes, [Ru(bpy)(2)(L)][PF6](2) are described. The ligands L bear a terbu toxypropyl chain substituent at position 2. We discovered that under b asic conditions condensation between an enolisable ketone and an alpha ,beta-unsaturated ketone gives exclusively the 1,2-addition isomers wi th good yields. In contrast to 2,2'-bipyridine, the annelated ligands L show fluorescence emission, probably due to the rigidity of the mole cules. Spectroscopic and photophysical results of the heteroleptic com plexes at room temperature and at 77 K are similar to the reference co mplex, [Ru(bpy)(3)](2+), except for less intense emission quantum yiel ds and lifetimes at room temperature. This behaviour is due to the pre sence of a substituent and its position adjacent to the nitrogen of th e annelated ligands engaged in the coordination, rather than to the ri gidity of these ligands. As shown by the crystallographic data, this s ubstituent induces a lengthening of the adjacent Ru-N bond (2.16 Angst rom as compared to 2.05 Angstrom for the other Ru-N bonds). As a resul t, the octahedral structure of the heteroleptic complexes is distorted and the probability of nonradiative processes is thus favoured.