EFFECTS OF AGING ON THE DYNAMICS OF RHODAMINE-6G IN TETRAMETHYL ORTHOSILICATE-DERIVED SOL-GELS

Static and dynamic fluorescence spectroscopy of rhodamine 6G (R6G) in a sol-gel matrix are used to study the effect of aging time and hydrol ysis pH on the local microviscosity. These results demonstrate that th e sol-gel formation cycle is composed of several distinct regions and that the average local microviscosity sensed by R6G changes by 2 order s of magnitude throughout the cycle. However, the probe is never compl etely immobilized as in a vitrified solvent. Dynamic anisotropy experi ments show that the R6G rotational reorientation dynamics are composed of two independent rotational correlation times. These are a manifest ation of the R6G reporting simultaneously from two discrete microdomai ns and not due to anisotropic rotational reorientation of R6G. These m icrodomains are discussed in terms of a simple two (one constant and o ne variable) microdomain model.