Water-soluble branched phenylene-ethynylene fluorophores with N-phenylcarbazole core

Three new water-soluble fluorophores containing N-phenylcarbazole core are synthesized by Sonogashira coupling of the triiodo core with arylethynes followed by ester hydrolysis or amino quaternization. In comparison with their analogs with triphenylamine core, these new fluorophores exhibit greater quantum efficiencies which could cause by the enhanced molecular rigidity. The quantum yield improvement is more pronounced in the systems devoid of intramolecular energy transfer (ICT) process. The fluorophore with salicylate peripheries exhibits a selective fluorescence switching-off by Cu2+ above 4 micromolar. Detailed investigations indicated that the peripheries on the carbazole nitrogen is responsible for fluorescent quenching, whereas those on the 3- and 6-position of carbazole function as the fluorescent signal amplifying units. The fluorescence switching-off is postulated to cause by synergetic works between superquenching induced by multiple complexation of Cu2+ with the fluorophore and quenching signal amplification fetched by efficient ICT.