In this work, spherical polymer-based fluorescent sensor with high sensitivity for Hg²⁺ was first designed and synthesized. Dendritic hyperbranched poly(phenylene sulfide) (HPPS) with an average molecular weight of 10.910 kD and spherical conformation was synthesized via one-pot reaction procedure with 2,4-dichlorothiophenol as monomer. Because of aryl groups conjugated with sulfur atoms and dendritic topology, HPPS displayed remarkable chemical stability, fluorescent and multiple reaction sites. It inspires us to employ it as a smart matrix to develop polymer fluorescent sensor. Through the nucleophilic substitution and hydrolysis reaction, peripheral Cl atoms of HPPS were modified by NH₂ groups, and the resulted HPPS-NH₂ was achieved. The fluorescent sensor (HPPSNT) was fabricated by HPPS-NH₂ azo N=N covalently bonded to small probe molecule Benzamide, N-[[[2-(phenylamino)ethyl]amino]thioxomethyl], which can react with Hg²⁺sensitively and selectively, causing desulfurization and cyclization. The results showed that HPPSNT sensor exhibited excellent sensitivity towards Hg²⁺, and can selectively recognize Hg²⁺ over other metal ions, such as Al³⁺, Ba²⁺, Cd²⁺, Cu²⁺, Fe³⁺, Zn²⁺, Pb²⁺, Mg²⁺, K⁺, Ag⁺. It was found that the decreased absorption of fluorescent signal intensity was proportional to the mercury content concentration in a range of 2.5～100 nmol/L with a coefficient of correlation R of 0.9931, and a detection limit of 0.46 nmol/L. The mechanism of high sensitivity was discussed. HPPS was rich in sulfur atoms inside, which has a strong affinity for Hg²⁺, Cu²⁺, Fe³⁺, Ag⁺, consequently, fluorescence of HPPS-NH₂ was quenched dramatically in the presence of these ions. As the peripheral small probe molecules preferentially reacted with Hg²⁺ via desulfurization and cyclization reaction, it is by such reactions instead of by quenching to cause fluorescence intensity of HPPSNT weakened. The decline of fluorescence intensity via desulfurization and cyclization reaction can be explained through the simulation calculation of bond length by Gaussian 09.

Key words: dendritic polymer, hyperbranched poly(phenylene sulfide), mercury ions, fluorescene, highly sensitive sensor