A method for preparing a cationic sulfoxide intermediate having the following formula wherein Ar1 and Ar2 are substituted or unsubstituted aryl groups that are the same or different, includes reacting hydrogen peroxide with (i) a compound having the following formula (2) or sulfonic acid R′SO3H, wherein R′ is CH3, CF3, phenyl, toluene, or OH, and (ii) a cationic thioether intermediate having the following formula (4) to obtain the cationic sulfoxide intermediate: wherein R is a substituted or unsubstituted C1-C6 alkyl group; and wherein Ar1 and Ar2 are as defined above and Y is an anion.