Synthesis, Characterization, and Selective Sr2+ Sensing Study of Copper(I)‐Bridged Calix[4]arene‐Based Binuclear Alkynylplatinum(II) Complexes

Three copper (I)-bridged p-tert-butyl-calix[4]arene tethering binuclear 6-aryl-2,2'-bipyridine (C^N^N) alkynylplatinum (II) complexes have been designed and synthesized. Their photophysical properties and sensing ability to strontium ions (Sr2+) have been investigated in terms of UV-vis absorption, emission, MS and 1H NMR. The binuclear complex bearing aza-[15]crown-5 pendants exhibited a unique emission enhancement at ca. 750 nm toward Sr2+ ion, a result of the alteration of the lowest excited state from non-emissive ligand to ligand charge transfer (LLCT) state to emissive metal-metal to ligand charge transfer (MMLCT) state. A 1:1 sandwiched binding mode between Sr2+ and the two aza[15]crown-5 moieties in the complex is proposed.