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-deri ved ormosil (organically modified silicate) are studied spectroscopica lly using the probe molecule 2,2'-bipyridinetriscarbonylchlororhenium( I) The emission band maximum of this molecule is known to shift to hig her energy as the viscosity of its local environment increases. The ra nge of this viscosity-dependent shift was measured in the fluid and fr ozen (20 K) ormosil sol and in each of the sol's components. Changes t hat occur during the processing of the ormosil were observed by measur ing the changes in the luminescence band maximum of the probe. The emi ssion maximum shifts gradually from 16300 +/- 300 cm(-1) in the sol (i ndicative of a fluid environment) to 17400 +/- 300 cm(-1) in dried orm osil. The final band position suggests that the probe molecule is trap ped in a flexible organic site. By cooling the dried gels, a further b lue shift in the luminescence of the probe molecule occurs. The proper ties of the ormosil are contrasted with those of silicate and aluminos ilicate sol-gel matrices.