Induced self-assembly and disassembly of water-soluble alkynylplatinum( ii ) terpyridyl complexes with switchable near-infrared (NIR) emission modulated by metalmetal interactions over physiological pH: demonstration of pH-responsive NIR luminescent probes in cell-imaging studies

Water-soluble alkynylplatinum( ii ) terpyridine complexes, [Pt{tpy(C 6 H 4 CH 2 NMe 3 -4)-4}(CCAr)](OTf) 2 [Ar = C 6 H 3 (OH) 2 -3,5 ( 1 ), C 6 H 4 OH-4 ( 2 ), C 6 H 3 (OMe) 2 -3,5 ( 3 )], have been synthesized and characterized. The photophysical and electrochemical properties of the complexes have been studied. Complex 1 has been found to undergo aggregation at low pHs, leading to metalmetal and/or interactions and the emergence of a triplet metal-metal-to-ligand charge transfer ( 3 MMLCT) emission in the near-infrared (NIR) region, the intensity of which has been enhanced 1350-fold over that at physiological pH. Such switchable NIR emission of complex 1 was employed in cell-imaging experiments. The pH response of the 3 MMLCT emission of complex 1 in cellular compartments has been studied using experiments with fixed MadinDarby canine kidney (MDCK) cells, while live cell-imaging experiments revealed that complex 1 could function as a NIR luminescent probe for the tracking of the location of acidic organelles such as lysosomes