Hemilabile coordination complexes for sensing applications

Complexes containing hemilabile ligands provide a potential site for the reversible binding of analytes to a transition metal center because of their dynamic chelating ability. Due to their ability to reversibly bind analytes, hemilabile coordination complexes have recently been explored for application as small molecule chemosensors. Hemilabile complex sensors based on a Ru(II) bipyridyl system containing phosphine ether ligands have been shown to exhibit an analyte-dependent absorbance and emission response. When small molecule ligands such as water, acetonitrile, triethylamine, dodecanethiol and dimethylsulfamide (L) are in the presence of (1), an equilibrium forms between (1) and (1·L), the coordination complex resulting from substitution of the labile ether position. The binding of the Lewis bases creates dramatic changes in the photoluminescence. These photophysical changes are manifested as energetic shifts in the absorption and emission spectra, as well as changes in the temperature dependence of the emission lifetime. The photophysical characterization of ruthenium hemilabile complexes for the detection of moisture and small molecules is reported and analyzed in light of molecular orbital energy changes. It is shown that ruthenium hemilabile complexes hold potential as reversible sensors that exhibit ligand-dependent absorbance and luminescent signals.