Showing papers by "Mitchio Okumura published in 1980"

Lifetimes, spectra, and quenching of the excited states of polypyridine complexes of iron(II), ruthenium(II), and osmium(II)

Abstract: The lifetimes of the excited states formed by 530-nm excitation of polypyridine complexes of iron(II) (FeL/sub 3//sup 2 +/) and osmium(II) (OsL/sub 3//sup 2 +/) have been determined by laser flash-photolysis techniques. The FeL/sub 3//sup 2 +/ lifetimes, measured in water at room temperature using picosecond absorption spectrometry, are as follows (L,tau +- sigma(ns)):2,2',2''-terpyridine (2.54 +- 0.13); 2,2'-bipyridine (0.81 +- 0.07); 4,4'-dimethyl(2,2'-bipyridine) (0.76 +- 0.04); 1,10-phenanthroline (0.80 +- 0.07); 4,7-(diphenyl sulfonate)-1,10-phenanthroline (0.43 +- 0.03). Lifetimes for the analogous complexes of osmium(II) lie in the range 10-100 ns under the same conditions. Unlike the excited states of Ru(bpy)/sub 3//sup 2 +/ and Os(bpy)/sub 3//sup 2 +/ (lambda/sub max/430-460 nm, epsilon approx. 5 x 10/sup 3/ M/sup -1/ cm-/sup 1/), the excited state of Fe(bpy)/sub 3//sup 2 +/ does not luminesce or absorb significantly in the visible (epsilon < 10/sup 3/ M/sup -1/ cm/sup -1/ at lambda greater than or equal to 350 nm) but does exhibit intense absorption below approx. 325 nm. Rate constants for the quenching of the excited states of polypyridine complexes of osmium(II) and ruthenium(II) by ground-state polypyridine complexes of iron(II), ruthenium(II), and osmium(II) are reported and are ascribed to either electron-transfer or energy-transfer processes. The excited statesmore » of tris(2,2'-bipyridine)iron(II) and of bis(2,2',2''-terpyridine)iron(II) undergo reaction with Fe/sub aq//sup 3 +/ (0.5 M H/sub 2/SO/sub 4/, 25/sup 0/C) with a rate constant less than or equal to 1 x 10/sup 7/ M-/sup 1/ s/sup -1/. Based on a comparison of its properties with those of the luminescent charge-transfer excited states of ruthenium(II) and osmium(II) polypyridine complexes the excited state of FeL/sub 3//sup 2 +/ is identified as a ligand-field state.« less