Venturi, M.; Marchioni, F.; Balzani, V., Opris, D.; Henze, O., Schlüter, A.D.
"A Photophysical and Electrochemical Investigation on a Phenylacetylene Macrocycle Containing Two 2,2'-Bipyridine Units, Its Protonated Forms, and Ru(II) and Os(II) Complexes"
Eur. J. Org. Chem. 2003, 4227-4233

The phenylacetylene macrocycle 1, which incorporates two 2,2'-bipyridine (bpy) chelating units in opposite sites in its shape-persistent structure, shows an intense absorption band in the UV spectral region (max = 305 nm, max = 118000 M-1cm-1) and a very strong fluorescence band in dichloromethane solution max = 381 nm, t = 0.8 ns, = 0.9). Upon titration with trifluoromethanesulfonic acid, the two bpy units are independently protonated with formation of a [1.2H]2+ species that shows a new absorption band with max = 355 nm (max = 42000 M-1cm-1) and a weak fluorescence (max = 520 nm). The dinuclear [(bpy)2Ru(1)Ru(bpy)2]4+ and [(bpy)2Os(1)Os(bpy)2]4+ complexes do not show any ligandcentred emission and exhibit absorption and emission bands in the visible region {[(bpy)2Ru(1)Ru(bpy)2]4+, absorption: max = 453 nm, emax = 19000 M-1cm-1; emission: max = 625 nm, t = 792 ns, F = 0.05; [(bpy)2Os(1)Os(bpy)2]4+ absorption: max = 488 nm, emax = 15500 M-1cm-1; emission: max = 740 nm, t = 59 ns, F = 0.003}. The photophysical behaviour of the macrocyclic ligand 1 and the dinuclear complexes at 77 K has also been investigated. The electrochemical properties of 1, the model compound ligand 3 and bpy ligand were investigated in purified tetrahydrofuran under vacuum conditions. The electrochemical behaviour of the dinuclear complexes was studied in argon-purged dichloromethane and compared with that of the model compounds [Ru(bpy)2(3)]2+, [Ru(bpy)3]2+, and [Os(bpy)3]2+. In the dinuclear complexes the two metal centres and the two 2,2'-bipyridine units of macrocycle 1 behave independently, as shown by the reversible bielectronic processes observed on oxidation and reduction. Both 1 and its dinuclear complexes contain reactive substituents and can therefore be used as starting components for the construction of photo- and redox-active supramolecular species. (Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim.