Dendritic polyelectrolyte fluorophores with n-aryl carbazole core

Abstract

Novel dendritric fluorophores are designed and synthesized using N-phenyl carbazole as the core and benzoate, salicylate, or quaternaryammonium as the pheripheral groups. The synthesis relies on Sonogashira couplings between the core and ethynyl benzenes with different substituents. Upon conversion of the peripheries into carboxylate or trimethylammonium groups, water-soluble fluorophores with quantum efficiencies greater than their triphenylamine-cored analogs are obtained. This improved quantum yields results from the enhanced structural rigidity, which decreases the geometrical relaxation of the excited molecules. However, this quantum efficiency improvement approach is more apparent in the case where the molecule is lack of the internal charge transfer phenomenon. In addition, it is found that the fluorescent signal of fluorophore with salicylate group can be selectively quenched by copper (II) ion. The non-linear relationship between fluorescent intensity and concentration of copper (II) ion reveals a turn-off fluorescent switching property for the copper (II) ion at 4 micromolar and above. The fractional investigation of this fluorophore indicates that the ethynyl salicylate group attached on the phenyl ring of the core is responsible for fluorogenic response towards copper (II) ion, where as the other parts of molecule function as fluorescent signal amplification units.