Improvement of the Dymanic Range of the pH Sensing by Using a Luminescent Tricarbonylpolypyrydilrhenium(I) Complex with Three Different Protontion Sites

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

INORGANIC CHEMISTRY

American Chemical Society

Lugar: Washington D.C; Año: 2008

0020-1669

The complex [Re(4,4’-(CO2H)2-bpy)(CO)3(4,4’-bpy)](CF3SO3), 1 (4,4’-(CO2H)2-bpy = 4,4’-dicarboxyl-2,2’-bipyridine, 4,4’-bpy = 4,4’-bipyridine), synthesized and characterized by spectroscopic techniques, displays a strong dependence of its photophysical properties on pH. From both emission intensity and lifetime measurements at different pH values, three values for the protonation constants of the excited states have been determined ( pKa1* = 1.8 ± 0.1, pKa2* = 3.9 ± 0.1 and pKa3* = 5.6 ± 0.1). The unusual bell-shaped variations of these photophysical properties can be accounted for by the changes of energy levels ordering induced by each protonation, as confirmed by TD-DFT calculations. Since the solubility, stability and dynamic range of pH sensing by 1 have been improved respect to similar tricarbonylpolypyridylrhenium(I) complexes, we conclude that 1 can be used as an efficient molecular switch of the on-off-on type.