A novel polytriarylamine (PTAA)-type alternating copolymer with on-chain crystal violet moieties has been generated which shows the expected strong dependence of its UV-Vis absorption spectrum from the pH value of the surrounding medium. Starting from the colorless leucocrystal violet form subsequent protonation/water elimination (by trifluoroacetic acid) leads to the formation of a blue colored, cationic copolymer with on-chain crystal violet units that displays a characteristic Vis absorption band peaking at 627 nm. Further protonation leads to the generation of the corresponding dicationic species which is accompanied by a red shift of the long wavelength absorption maximum to 713 nm. The novel pH-sensitive polytriarylamine derivatives will be investigated as potential p-type semiconductors for OFET (gas) sensors.