Synthesis and photophysical properties of dinuclear organometallic rhenium(I) diimine complexes linked by pyridine-containing macrocyclic: Phenylacetylene ligands

Two novel pyridine-containing hexagonal phenylacetylenic macrocyclic ligands have-been synthesized from Pd-catalyzed cross-coupling or Cu-catalyzed oxidative coupling reactions. The se ligands have been subsequently us ed to prep are dinuclear 4,4'-di-tert-butyl-2,2'-bipyridine Re(I) tricarbonyl complexes. Both ligands and complexes show strong luminescence in room-temperature solution. There is no concentration dependence in the H-1 NMR spectra for these ligands and complexes, which rules out ground-state self-association. However, both of the free ligands exhibit concentration-dependent fluorescence. The fluorescence bands' of the ligands are red-shifted with increasing concentration,:and this behavior is ascribed to the formation of excimers in the excited states. In contrast, both of the organometallic complexes do not exhibit any concentration-dependent luminescence.