Research On Novel Fluorescent Probes For Heavy Metal Ions Based On 1, 8-Naphthalimide

A series of novel fluorescent probes for heavy metal ions: 4-(2'-N,N-dimethylaminoethylamino)- N-n-butyl-1,8-naphthalimide (MBN), 4-(2'-N,N-dimethylaminoethylamino)- N-(2-dimethylaminoethyl)-1,8-naphthalimide (MMN), 4-(2'-N,N-diethylaminoethylamino)- N- n-butyl-1,8-naphthali mide (EBN), 4-(2'-N,N-diethylaminoethylamino)- N-(2-diethylaminoethyl)-1,8-naphthalimide (EEN) were designed and synthesized from 1,8-naphthalimides and aliphatic amines. Their structures were characterized by FTIR, MS, 1H-NMR and elementary analysis.Study on photo-physical properties in DMF of the probes showed that UV-Vis absorption and fluorescence maxima wavelengths of the probes were red-shift as the polarity of the solvents increased. When the concentration rose, the fluorescence intensity increased at first, then decreased and got the maximums at 5*10^-5mol/L. The fluorescence intensity of the probes depended significantly on pH value, and the probes exhibited stronger fluorescence in acidic condition. Between pH 5.0 to 11.0, the fluorescence intensity dropped linearly when the pH value rose.The research of recognizing heavy metal ions by the probes indicated that: MBN, MMN, EBN and EEN behaved as novel highly sensitive and selective fluorescent probes for Fe³⁺ ions in DMF. In the range of 1.0×10^-5～1.0×10^-4 mol/L Fe³⁺, the fluorescence intensity of the probes had good linearly relationship with the concentration of Fe³⁺. Furthermore, the detection limits, the association constant and the chelation mechanism were analyzed and it was found that 2:1 matal/probe complex was formed. The rank of the selectivity and sensitivity to Fe³⁺ from high to low were EBN>MMN>EEN>MBN and EBN>EEN>MBN> MMN, respectively.