A highly selective and sensitive fluorescent sensor based on a 1,8-naphthalimide with a Schiff base function for Hg2+ in aqueous media

A new fluorescent sensor, N-allyl-4-[(2-(3-methoxysalicylaldimino)ethylamino]-1,8-naphthalimide (HL), for Hg2+ has been developed where the Schiff base substituent acts as a recognition group. This sensor shows a large Stokes shift of 3535-4042 cm(-1) and a general fluorescence quantum yield of 0.05, 249-0.11, 866 in organic solvents of different polarity as expected. It also exhibits highly selective and a sensitive response to Hg2+ (CYRILLIC CAPITAL LETTER EFHg+HL/CYRILLIC CAPITAL LETTER EFHL = 2.28) over other metal ions (Na+, K+, Ca2+, Mg2+, Al3+, Pb2+, Fe3+, Ni2+, Zn2+, Cu2+, Ag+, Co2+, Cr3+, Mn2+ and Cd2+) in solution (DMF/Tris-HCl buffer, 1:1, v/v, pH = 7.2). The Hg2+-induced fluorescence enhancement at 526 nm is proportional to the concentration of Hg2+ in the range of 0.5-4.0 mu m with a detection limit of 0.18 mu m. Based on the fluorescence titration and a Job's plot analysis, the metal-to-ligand ratio of the complex is 2:1 with a binding constant of 1.56 x 10(12) m(-1).