PHOTOCHEMISTRY OF BIS(2,2'-BIPYRIDYL)(METHYLENE-LINKED DIAMINE)RUTHENIUM(II) COMPLEXES, [RU(BIPY)2(L)]2+ (L=H2N-(CH2)N-NH2N=2 AND 3)

The photophysical processes and photochemical reactions of bis(2,2'-bipyridyl)(methylene-linked diamine)-ruthenium(II) complexes, [Ru(bipy)2L]2+ (bipy = 2,2'-bipyridyl; L = H2N-(CH2)n-NH2;n = 2, 3) have been examined in order to study the effect of the chain length of the diamine ligands on photosubstitution reactions. The low temperature (77 K) emission properties, luminescent lifetimes and the temperature dependence of the emission intensities were similar for both complexes but much reduced compared with tris(2,2'-bipyridyl)ruthenium(II). Low values of quantum yields for the replacement of the diamine ligand by Cl- anions in CH3CN and CH2Cl2 solutions were found for both n = 2 and n = 3 complexes although the photosubstitution reactions have low apparent activation energies. Bis(2,2'-bipyridyl)(ethylenediamine)ruthenium(II) showed a lower quantum yield than bis(2,2'-bipyridyl)(1,3-propylenediamine)ruthenium(II) reflecting the fact that the complex with larger chelate ring bas a less efficient ring reclosure process. Extended photolysis afforded oxidation of the methylene linked ligand, such that, in pure CH3CN and H2O, bis(2,2'-bypyridyl)(ethylenediamine)ruthenium(II) underwent a photo-oxidation process which transformed the ethylenediamine ligand into a coordinated 1,2-ethylenediimine ligand.