A fluoride-selective PCT chemosensor based on formation of a static pyrene excimer

[GRAPHICS] Calixarene-based fluorescent chemosensor 1 with two fluorogenic pyrene units conjugated to amide groups as guest recognition sites is synthesized. Complexation of F- by 1 causes a red shift of its absorption band to 400 nm (Delta lambda = 54 nm) and a blue shift of the excimer emission to 470 nm (Delta lambda = 12 nm) together with enhanced fluorescence intensity. The blue-shifted excimer emission is attributed to a pyrene dimer formed in the ground state, a so-called static excimer.