Light-Emitting Molecular Machines: pH-Induced Intramolecular Motions in a Fluorescent Nickel(II) Scorptionate Complex

摘要

A cyclam-like macrocycle has been synthesized with a pendant arm containing a dansylamine group. In the corresponding nickel(II) complex, binding of the pendant arom to the metal is pH controlled. In particular, at pH 4.3, the sulfonamide group deprotonates and coordinates the Ni~(II) center, giving rise to a complex of trigonal bipyramidal stereochemistry, as shown by X-ray diffraction studies performed on the crystalline complex salt. At pH 7.5, an OH~- ion binds the metal and a six-coordinate species forms. The binding-detachment of the pendant arm to/from the Ni~(II) center is signaled by changes in the emission properties of the dansyl subunit in the side chain; the fluorescence of this side chian is high when the pendant arm is not coordinated and low when the sulfonamide group is bound to the metal. The system investigated represents the prototype of a light-emitting molecular machine, driven by a pH change.