Preparation And Property Studies Of 1,8-Naphthalimide-based Fluorescent Probes

The accumulation of heavy metal ions and picric acid ions in the living body seriously threatens the safety of various living organisms.From this standpoint,it is noteworthy that the detection of these ions is,therefore,of high practical significance.The fluorescence molecular probe detection method is not only simple and convenient,but also has outstanding advantages in terms of sensitivity,selectivity,response time,in-situ measurement（such as in fluorescence imaging technology）and long-distance detection using optical fibre,and therefore,traditional receptor molecule.The research field of attaching fluorophores and constructing supramolecular fluorescence probes for metal ions detection has received much attention.The 1,8-naphthalimide compound has good photochemical stability,thermal stability,and versatility of material modification,and can be used for constructing organic light-emitting diodes,fluorescent probes and/or sensors,DNA intercalating substances,and anticancer drugs,etc.The 1,8-naphthalimide derivatives have attracted attention due to their high fluorescence quantum yields,large Stokes shifts,adjustable photophysical and photochemical properties,and good light stability.In recent years,fluorescent probes using naphthalimide as the chromophore unit have received much emphasis in the sensing science research field.In this thesis report,the 1,8-naphthalimide is being selected as the chromophore whilst carboxyl group,amide,and Schiff base are being used as the recognition groups.Five naphthalimide derivative fluorescent ion probes were designed and synthesised,viz.:N-allyl-4--N-ethylenediamine-N,N-（di-3-propionicacid）-1,8-naphthalimide（S1）,N-n-butyl-4-N-ethylenediamine-N,N-（di-3-propionicacid）-1,8-naphthalimide（S2）,N-benzyl-4-N-ethylenediamine-N,N-（di-3-propionicacid）-1,8-naphthalimide（S3）,N-allyl-4-（ethylenediamine-5-methylsalicylidene）-1,8-naphthalimide（S4）and N-allyl-4-iminodi（N-benzylacetamide）-1,8-naphthalimide（S5）.The recognition properties of these probes for the detection of metal ions and picric acid ions were studied.This thesis is split into the following four parts:Firstly,the introduction of the research progress of fluorescent probes.Secondly,the report of fluorescence quenching copper ion fluorescent probes.Fluorescence quenching copper ion fluorescent probes S1 S3 with 1,8-naphthalimide as the chromophore and carboxylic group as the recognition group were designed and synthesised.In DMSO/HEPES（1:1 v/v,pH 7.4）solution,the fluorescence quenching of Cu²⁺ion reached the level of 79.79%,meanwhile,the other metal ions did not interfere with Probe S1.The Job experiment s working line of the probe and mass spectrometry analysis showed that the probe lost a proton and Cu²⁺ion.The ion forms a 1:1 complex;the binding constant and detection limit are 1.14 x 10⁶M^-1and 4.67 x 10^-8M,respectively,indicating that the probe has both high sensitivity and selectivity.The fluorescence quenching of Probe S1by Cu²⁺ion can be attributed to the combined effects of the single-electron effect of divalent Cu²⁺ion and the anti-light-induced electronic effects of the coordination.The probe can be applied for the detection of Cu²⁺ion in real water samples.Meanwhile,the fluorescence quenching of Probe S2 by Cu²⁺ion reached the level of 75.41%,and the binding constant and detection limit are 5.54 10⁵M^-1and 4.33 10^-9M,respectively.The fluorescence quenching of Probe S3 by Cu²⁺reached the level of 83.67%,and the binding constant and detection limit are 1.37 10⁶M^-1and 0.69 10^-8M.Thirdly,the report of a fluorescence-enhanced mercury ion fluorescence probe.A fluorescent enhanced Hg²⁺ion fluorescent Probe S4 with 1,8-naphthalimide as the chromophore and Schiff base as the recognition group was designed and synthesised.Through elemental analysis,infrared spectroscopy,ultraviolet spectroscopy,nuclear magnetic resonance spectroscopy,mass spectrometry and other methods,they were characterised.Ultra-violet and fluorescence spectroscopies were used to investigate the photophysical properties and metal recognition properties of Probe S4.When the metal ions Na⁺,K⁺,Ca²⁺,Mg²⁺,Al³⁺,Pb²⁺,Fe³⁺,Ni²⁺,Cu²⁺,Zn²⁺,Ag⁺,Co²⁺,Cr³⁺,Mn²⁺,and Cd²⁺were added to Probe S4,no significant change in the fluorescence intensity of Probe S4 was found.After adding Hg²⁺,the fluorescence intensity of Probe S4 was significantly enhanced.The experimental results show that in DMF/Tris-HCl（v:v 1:1,p H 7.2）buffer,Probe S4 is highly selective for Hg²⁺recognition.Meanwhile,other metal ions have almost no effect on the fluorescence intensity of Probe S4.With the continuous increase of Hg²⁺ion,the fluorescence intensity of Probe S4 was continuously enhanced.When the added Hg²⁺content reached 0.5 equivalent,the fluorescence intensity of the Probe S4 also reached a maximum value and the fluorescence intensity attained a plateau.No obvious change took place after further additions.The results show that the coordination pattern between Probe S4 and Hg²⁺may be 2:1 and it was found from the Job graph that the coordination ratio between Probe S4 and Hg²⁺is exactly 2:1.The binding constant of Probe S4 to Hg²⁺is 7.35 x 10¹¹M^-1,indicating a strong binding ability between Probe S4 and Hg²⁺.In addition,when the concentration of Hg²⁺is between 0.5-4 M,the fluorescence intensity of Probe S4 has a good linear relationship and can be used for the quantitative detection of Hg²⁺.The detection limit of Probe S4 is obtained from the detection limit formula:C_DL 3/k and is calculated to be 0.26 M.The above results reveal that Probe S4 shows good recognition performance for Hg²⁺ion.Lastly,the report of a fluorescence quenching picric acid ion fluorescent probe.A fluorescent quenching picric acid ion fluorescent Probe S5 with 1,8-naphthalimide as the chromophore unit and amide as the recognition group was designed and synthesised.In DMF–H₂O（15:1）system,the recognition of picric acid ion by Probe S5 was studied by carrying out selectivity experiment,fluorescence titration experiment,ion competition experiment,and pH influence experiment.The results of the identification and sensitivity experiments showed that Probe S5 has a high affinity for picric acid ion without any interference suffered from various competitive anions like F^-,Cl^-,Br^-,I^-,OH^-,Ac^-,NO₃^-,Cl O₄^-,SCN^-,SO₃^2-,SO₄^2-,H₂PO₄^-,and HPO₄².The detection limit was calculated as 6.6 10^-7M and it was speculated that the mechanism of possible fluorescence quenching involves the electron transfer from the naphthalimide compound.The recognition of the picric acid ion may be that the picric acid ion’s oxygen atom forms intermolecular molecular hydrogen bonds with the nitrogen-hydrogen of the amide in Probe S5 resulting in a surplus of the electrons on the chromophore so that the electron transfer process is enhanced to cause fluorescence quenching.