THE USE OF THE RIGIDOCHROMISM OF RECL(CO)(3)-2,2'-BIPYRIDINE AS A PROBE OF GELATION, AGING AND DRYING IN SOL-GEL-DERIVED ORMOSILS

Changes that occur during gelation, aging and drying of a sol-gel-derived ormosil (organically modified silicate) are studied spectroscopically using the probe molecule 2,2'-bipyridinetriscarbonylchlororhenium(I) The emission band maximum of this molecule is known to shift to higher energy as the viscosity of its local environment increases. The range of this viscosity-dependent shift was measured in the fluid and frozen (20 K) ormosil sol and in each of the sol's components. Changes that occur during the processing of the ormosil were observed by measuring the changes in the luminescence band maximum of the probe. The emission maximum shifts gradually from 16300 +/- 300 cm(-1) in the sol (indicative of a fluid environment) to 17400 +/- 300 cm(-1) in dried ormosil. The final band position suggests that the probe molecule is trapped in a flexible organic site. By cooling the dried gels, a further blue shift in the luminescence of the probe molecule occurs. The properties of the ormosil are contrasted with those of silicate and aluminosilicate sol-gel matrices.