COMPARISON OF SOLVENT AND PROBE REORIENTATION IN POLYACRYLAMIDE GELS

Raman spectroscopy and time-resolved fluorescence anisotropy decay wer e used to measure the rotational relaxation dynamics of acetonitrile a nd the dianion polyphenyl 2 (PP2) in polyacrylamide (PAA) gels in a wa ter-acetonitrile solvent mixture. In the neat solvent mixture the acet onitrile molecule rotates, underlying a reduced friction in comparison to its dynamics in pure acetonitrile. The rotational behavior of PP2 in the mixture is well described by the Stokes-Einstein-Debye equation . In the PAA gels the rotational relaxation of acetonitrile is only we akly influenced by the gel network even at high polymer concentrations . In contrast, the larger probe,molecule PP2 reflects a significant re tardation of the reorientational motion with increasing PAA concentrat ion. We suggest that this behavior results from the different environm ents experienced by the probe and solvent molecules.