COUNTERION-DEPENDENT REORIENTATION DYNAMICS OF AN OXAZINE IN POLAR PROTIC AND APROTIC-SOLVENTS

The rotational diffusion characteristics of oxazine 725 perchlorate and chloride have been measured in several polar protic and aprotic solvents. Oxazine 725 salts exhibit counterion-dependent reorientation in methanol and acetonitrile, but not in 1-propanol, 1-hexanol, N,N-dimethylformamide, dimethyl sulfoxide, or water. Counterion-dependent reorientation arises from the associative ion pair formed in solution between the oxazine 725 cation and its counterion. The observation of counterion-dependent reorientation is shown to depend not only on the degree of complexation of each salt but also on the reorientation times of the different species present in solution.