PHOTOPHYSICAL AND PHOTOCHEMICAL STUDIES OF RUTHENIUM TRIS(BIPYRIDINE) ON HECTORITE

The nature of the interaction of ruthenium tris(bipyridine) with an aqueous clay colloid has been investigated by both steady-state and time-resolved photophysical and photochemical techniques. Time-resolved emission spectra display a red shift in the emission maximum over time. Results of kinetic and spectral analyses indicate the existence of two distinct adsorption environments for the luminescent probe molecule on the flat clay surface. Each type of adsorption of the probe molecule results in a unique lifetime and emission spectrum, which are obtained through mathematical deconvolution of observed data based on a multiexponential model. Additional experiments utilizing clay powders and films, luminescence quenching reactions, ion-exchange measurements, and chemical modifications of the clay surface provide evidence for the nature of the distinct adsorption mechanisms. An interpretation is proposed on the basis of the existence of two different types of adsorption zones at the surface of the clay. At one type of adsorption zone the water is held rigidly and presents an environment to the ruthenium tris(bipyridine) probe that results in a short lifetime and a blue-shifted emission. The second absorption zone involves a stronger interaction directly with the clay surface so that the photophysics are less influenced by the nature of the surrounding water. Direct comparison of photophysical properties of the luminescent probe on the clay and in ice at -20°C supports the model. © 1990 American Chemical Society.