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 hydrolysis pH on the local microviscosity. These results demonstrate that the sol-gel formation cycle is composed of several distinct regions and that the average local microviscosity sensed by R6G changes by 2 orders of magnitude throughout the cycle. However, the probe is never completely immobilized as in a vitrified solvent. Dynamic anisotropy experiments show that the R6G rotational reorientation dynamics are composed of two independent rotational correlation times. These are a manifestation of the R6G reporting simultaneously from two discrete microdomains and not due to anisotropic rotational reorientation of R6G. These microdomains are discussed in terms of a simple two (one constant and one variable) microdomain model.