In this research project the effects of counter-ion-exchanged zeolites on the oxidation of para-substituted diaryl radicals to carbocations were investigated using state-of-art nanosecond laser diffuse reflectance spectroscopy. Diaryl radicals were generated by photo-induced decarboxylation of diaryl acetic acids. It was found that diaryl radicals are not directly oxidized to the respective carbocations; instead it was suggested that the carbocation is generated from the excited-state radical. It was also found that diaryl radicals appear to be stabilized by larger counter-ions, whereas carbocations are more stable in the presence of small counter-ions such Li+.