Proton-Induced Luminescence of Mono- and Dinuclear Rhenium(I) Tricarbonyl Complexes Containing 4-Pyridinealdazine

CATTANEO, MAURICIO; FAGALDE, FLORENCIA; KATZ, NÉSTOR E.

INORGANIC CHEMISTRY

American Chemical Society

Lugar: Washington D.C, EE.UU; Año: 2006 vol. 45 p. 6884 - 6891

0020-1669

ABSTRACT New mono- and dinuclear rhenium(I) tricarbonyls, of formulae [Re(bpy)(CO)3(PCA)]+ (1), [(bpy)(CO)3ReI(PCA)ReI(CO)3(bpy)]2+ (2) , and [(bpy)(CO)3ReI(PCA)RuII(NH3)5]3+ (3),  (bpy = 2,2´-bipyridine, PCA = 4-pyridinecarboxaldehyde azine) have been synthesized as PF6- salts and characterized by spectroscopic, electrochemical and photophysical techniques.  These species do not emit at room temperature in CH3CN; however, in aqueous solutions, a decrease in pH induces luminescence in all of them, due to protonation of one of the N atoms of the ?C=N-N=C-  chain of PCA, as indicated by the pKa values of the ground states, obtained by absorption measurements, which are ca. three  orders of magnitude lower than the pKa value of the pyridine N of PCA in complex 1. On the other hand, the values of pKa* of the excited states, obtained by emission measurements, of complexes 1 and 2 are similar (pKa* = 2.7 ± 0.1, at I = 0.1 M) and higher than those of the corresponding ground sates. At low values of pH, chemical decomposition takes place rapidly in complex 3, but not in 1 and 2, supporting the possible use of these latter species as luminescent sensors of pH. The heterodinuclear complex, of formula [(bpy)(CO)3ReI(PCA)RuIII(NH3)5]4+, was obtained by bromine oxidation of the [ReI,RuII] precursor in CH3CN solution; from spectral and electrochemical measurements, the recombination charge transfer reaction [ReII, RuII ] ® [ReI, RuIII], that occurs after photo-excitation, is predicted to lie in the Marcus inverted region.