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

Abstract

Water-soluble alkynylplatinum(II) terpyridine complexes, [Pt{tpy(C6H4CH2NMe3-4)-4′}(C[triple bond, length as m-dash]C–Ar)](OTf)2 [Ar = C6H3–(OH)2-3,5 (1), C6H4OH-4 (2), C6H3–(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 metal–metal and/or π–π interactions and the emergence of a triplet metal-metal-to-ligand charge transfer (3MMLCT) 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 3MMLCT emission of complex 1 in cellular compartments has been studied using experiments with fixed Madin–Darby 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.