Journal of Physical Chemistry, Vol.98, No.1, 17-22, 1994
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.
Keywords:HYDROCARBON REGION;FLUORESCENT PROBES;GLASSES;VISCOSITY;PHASE;MICROVISCOSITY;TRANSITION;DIFFUSION;SENSORS;SILICA