A series of platinum(II) terpyridine complexes featuring an aminostilbene donor-acceptor framework was synthesized. The complex with a dithiaazacrown moiety exhibits a highly sensitive and selective colorimetric response to a Hg2+ cation through modulation of the relative strength of ICT and MLCT transitions. The results from H-I NMR titration suggest the existence of a weak Pt-II...Hg-II metallophilic interaction at low Hg2+ concentration.