Synthsis of naphtalimide fluorophores for mercury ion sensing

Abstract

Five difference naphthalimide derivatives (1-5) based on 2-(3-(2-aminoethylsulfanyl)propylsulfanyl)ethanamine were prepared for utilizing as selective Hg²⁺ sensors. The compounds were prepared by a conventional two-step or three-sep synthesis using inexpensive starting materials. The sensitive and selective binding behaviors of the sensors were investigated by fluorescence spectroscopy. Sensors 1 and 2 selectively bind Hg²⁺ by exhibiting OFF-ON fluorescence enhancement behaviors of the monomer and/or excimer bands. On the other hand, sensors 3 and 4 senses Hg²⁺ by exhibiting ON-OFF fluorescence quenching behavior in dichloromethane and acetonitrile solutions. Sensors 1-4 provide excellent Hg²⁺-selectivity and discriminate various competing metal ions such as Pb²⁺, Na⁺, K⁺, Mn²⁺, Cd²⁺, Ni²⁺, Ca²⁺, Li⁺, Zn²⁺ and Co²⁺. These optical sensors exhibited detection limits in the range of 10⁻⁷ – 10⁻⁶ M which are sufficient for the detection of sub-micromolar concentrations of Hg²⁺ ions found in environmental and many biological systems.