The N-atoms in two polymers, poly(4,4＇-dinonyl-5,5＇-bithiazole-2,2＇-diyl-co-5-tert-butylphenylene-1,3-diyl) (PBT) and poly(4,4＇-bis(p-dodecylphenyl)-2,2＇-bithiazole-5,5＇diyl) (DBT), have been quaternized by the reaction of the polymer with methyltriflate to give their respective N-methylated derivatives, MPBT and MDBT. Quaternization of the ring nitrogen atom lowers the energy levels of both the HOMO and LUMO and, hence, alters those polymer properties which are dependent on these energy levels. Both the absorbance and emission spectra red shift upon methylation, and the electrochemical reduction potential increases by 0.88 V. An increase of up to 8 orders of magnitude was also observed in the conductivity.