A series of platinum(II) terpyridyl alkynyl complexes that have been derivatized with basic amino functionalities, [Pt(tpy)(Cequivalent toC-C6H4-NR2-4]X (X = OTf-, R = CH3 1, R = CH2CH2OCH3 2, R = H 3; X = Cl- R = CH3 4, R = CH2CH2OCH3 5, R = H 6) (tpy = 2,2':6',2"-terpyridine), have been synthesized and characterized. Their photophysical responses at various acid concentrations were studied. The abilities of the complexes to function as colorimetric and luminescence pH sensors were demonstrated with dramatic color changes and luminescence enhancement upon introduction of acid.