PHOTOPHYSICS OF SUPERCOMPLEXES - ADDUCT BETWEEN RU(BPY)(CN)(4)(2-) AND THE [32]ANE-N8H88+ POLYAZA MACROCYCLE

The formation of a supercomplex between the Ru(bpy)(CN)(4)(2-) (bpy = 2,2'-bipyridine) complex and the [32]-ane-N8H88+ macrocycle (1) has be en studied in water and in acetonitrile. In acetonitrile, supercomplex formation is accompanied by (i) large hypsochromic shifts in the abso rption spectrum (color changes from deep violet to yellow) and in the emission spectrum, (ii) large anodic shifts in standard oxidation (0.7 3 V) and reduction (0.37 V) potentials, (iii) typical shifts of H-1-NM R signals for the macrocycle N-bound protons and the complex bipyridin e protons, and (iv) a large increase in the MLCT excited-state lifetim e of the complex. In water, the spectral shifts and the changes in sta ndard potential are much less pronounced, but supercomplex formation i s evidenced by C-13-NMR (and H-1-NMR) and by emission lifetime changes . In both solvents, supercomplex formation is complete in 1:1, 1.0 x 1 0(-4) M solutions, indicating very large stability constant values. A structure of the supercomplex with the macrocycle bound in a ''boat'' conformation to the four cyanide ligands of the complex, plausible in terms of molecular models, is consistent with all the experimental dat a. In water, the supercomplex further associates with added negative s pecies containing carboxylate functions, as shown by partial reversal of the lifetime changes. When the added species is also a potential el ectron transfer quencher (such as, e.g., Rh(dcb)(3)(3-), dcb = 4,4'-di carboxy-2,2'-bipyridine), however, association is not accompanied by q uenching. This behavior is attributed to the structure of the supercom plex-quencher adduct, in which the macrocycle acts as an insulating sp acer between the excited complex and the quencher.