Design,Synthesis And Properties Of Cationic Responsive Near Infrared Fluorescent Molecules

Compared with other detection methods,fluorescence detection has the advantages of specific recognition,simple and convenient operation and visual detection.It has become one of the important methods for metal ion detection in environmental and biological systems.So far,existing fluorescent probes mostly emit light in the visible range?400-650 nm?,while fluorescent probes emitting in the near-infrared?NIR,650-900 nm?are less reported.The near-infrared fluorescent probe has the advantages of small damage to the biological matrix,deep tissue penetration and small interference of biological background fluorescence.It has become a research hotspot of fluorescence detection and fluorescence imaging technology.In this paper,six near-infrared fluorescent probes were designed and synthesized by Schiff base reaction,and the reaction conditions were mild and the conversion rate was high.The specific detection performance of the prepared fluorescent probes for three metal ions of iron,mercury and copper in biological systems was explored.The main work content is as follow:1?The fluorophore parent molecule 9-?2-carboxyphenyl?-6-?diethylamino?-4-[?1-methyl-1H-indol-3-yl?methylene]-1,2,3,4-tetrahydroxanthylium?ICPDT,fluorescence emission wavelength is at 700 nm?was designed and synthesized by the mechanism of the rhodamine derivative having the fluorescence"on/off"with the opening and closing of the spironolactam in the molecule.The spironolactam compound ADMT was synthesized with hydrazine hydrate.Two near-infrared fluorescent molecules were obtained by Schiff base reaction:?1?6'-?diethylamino?-2-[?3,5-difluorobenzylidene?amino]-4'-??1-methyl-1H-indol-3-yl?meth ylene?-1',2',3',4'-tetrahydrospiro[isoindoline-1,9'-xanthen]-3-one?RHCF?,?2?6'?diethylamino?-2-[[?8-hydroxyquinolin-2-yl?methylene]amino]-4'-[?1-methyl-1H-indol-3-yl?methylene]-1',2',3',4'-tetrahydrospiro[isoindoline-1,9'-xanthen]-3-one?RHCC?.The molecular structure was analyzed and characterized by nuclear magnetic resonance?NMR?and time-of-flight mass spectrometry?TOF-MS?.The specific recognition and detection of iron ions(Fe³⁺)in aqueous systems by two fluorescent molecules were carried out by UV-vis spectrophotometry?UV-vis?and fluorescence spectroscopy.The results show that two probes can specifically recognize Fe³⁺and have strong anti-interference ability.The binding ratio of RHCF and RHCC to Fe³⁺is 1:1,and their complexation constants are 1.06×10⁵ M^-1 and 5.81×10⁴ M^-1,respectively.The detection limits are 6.40×10^-7 M and 1.20×10^-77 M,respectively.Fluorescence imaging experiments of A549 cells and zebrafish showed that RHCF and RHCC can monitor Fe³⁺in biological systems.2?Compounds 6'-?diethylamino?-2-[?2-pyridinecarboxaldehyde?amino]-4'-??1-methyl-1H-indol-3-yl?methylene?-1',2',3',4'-tetrahydrospiro[isoindoline-1,9'-xanthen]-3-one?L1?,6'-?diethylamino?-2-[?3-pyridinecarboxaldehyde?amino]-4'-??1-methyl-1H-indol-3-yl?methylene?-1',2',3',4'-tetrahydrospiro[isoindoline-1,9'-xanthen]-3-one?L2?and 6'-?diethylamino?-2-[?4-pyridinecarboxaldehyde?amino]-4'-??1-methyl-1H-indol-3-yl?methylene?-1',2',3',4'-tetrahydrospiro[isoindoline-1,9'-xanthen]-3-one?L3?were designed and synthesized.The above compounds were characterized by NMR and LC-MS.The results of UV-vis and fluorescence spectroscopy indicate that L1 has high selectivity to copper ions(Cu²⁺).When complexed with Cu²⁺,it emits 690 nm fluorescence,and the solution changes from colorless to green,enabling naked-eye detection.The complexation ratio of the probe L1 to Cu²⁺was found to be 1:1,and its detection limit and complexation constant were 4.40×10^-7 M and 5.89×10⁴ M^-1,respectively.Fluorescence imaging experiments prove that probe L1 can detect Cu²⁺in living organisms.3?The spironolactam compound ADMT and 4-fluorobenzaldehyde are reacted by Schiff base to obtain 6'-?diethylamino?-2-[?4-fluorobenzaldehyde?amino]-4'-??1-methyl-1H-indol-3-yl?meth-ylene?-1',2',3',4'-tetrahydrospiro[isoindoline-1,9'xanthen]-3-one?NIR-Hg?.The results of UV-vis and fluorescence spectroscopy indicated that NIR-Hg can selectively detect mercury ions(Hg²⁺)with a low detection limit(3.40×10^-7 M).The complexation constant of the probe is 4.43×10⁴ M^-1.After complexing with Hg2+,the color of the probe solution changes from colorless to green,enabling naked eye detection.A549 cells and zebrafish experiments have shown that NIR-Hg can be used as a detection probe in vivo.