Switching of intramolecular charge transfer in cruciforms: Metal ion sensing

Three different cruciforms containing the 1,4-bis-4′-pyridylethynyl-2,5-distyrylbenzene or the 1,4-bis-phenylethynyl-2,5-distyrylbenzene unit were synthesized and investigated with respect to their metal sensing properties. Upon addition of metal cations to these cruciforms, either a bathochromic or hypsochromic shift in emission and absorption is observed. The shift depends on whether the metal coordinates preferentially to the pyridine or to the dibutylaniline branches of the cruciforms. The three cruciforms were exposed to a selection of metal cations in dichloromethane, and their emission was examined. The cruciforms show differential sensing of metal cations, that is, different metals can be specifically discerned upon exposure to three cruciforms but not when exposed to only one. The system can discern calcium from magnesium cations and silver from mercury or lithium cations.