Synthesis and reversible control of the fluorescent properties of a divalent tin dipyrromethene.

A fluorescent chlorostannylene bearing a dipyrromethene ligand was synthesized. Its fluorescence quantum yield was low, Phi(f) = 0.04, probably because of the existence of the lone-pair orbital energetically close to the pi orbital. However, its fluorescence emission was increased to Phi(f) = 0.42 by dechlorination using silver triflate. The resulting cationic species reverted again to the chlorostannylene upon reaction with tetrabutylammonium chloride, with a corresponding weakening of the fluorescence.