A Novel Crown Ether Bridge Squaraine Dyes:Synthesis,Properties And Application

Crown ethers,a family of well-known "host molecules",possess a well-defined cavity,endowing them demonstrated distinctive ionophoric properties toward many guest molecules,including inorganic and organic species.Squaraines are a group of near-infrared dyes possessing excellent fluorescence emission and electrochemical properties,and have characteristics of good optical stability and easy to modify.Owing to their unique photophysical properties,many functionalized squaraine dyes have been synthesized and applied in various fields."Aggregation-caused quenching"is a common mechanism in fluorescence probes,and its reverse process from aggregation to disaggregation could cause a recovery or enhancement of fluorescence signal.Therefore,designing fluorescence probes for the detection of mental ions based on the mechanism of "aggregation and disaggregation",can be widely applied in various fields.According to the special properties of squaraines and crown ethers,we have now designed and synthesized a novel crown ether bridged squaraine fluorescent probe on the basis of previous work,which has been successfully applied to respond with Fe3+and Pb2+.The structure has been characterized by IR,ESI-MS,1H NMR,and 13C NMR,and the basic spectroscopic properties and Ion recognition of these crown ether bridged squaraine dyes have been studied.(1)A series of crown ether bridged squaraine dyes SQ-(1-3)have been designed and synthesized.The introduction of the ether chain,not only improve the stability and solubility of squaraine dyes.Crown ether bridged on squaraine dyes but also can form the structure of cavity,make its ability to capture with metal ions.(2)Aggregation of probes is usually due to high concentration.However,some organic groups(such as crown ethers,polyamines,macrocyclic amines,pyridines and acetates)of the reporters can form strong non-covalent interactions with metal ions,and then induce the formation of compounds,which results in aggregation and fluorescence quenching.This process is called "mental-coordinated aggregates".The new fluorescence probes SQ-1 and SQ-2,which has realized the detection of Fe3+based on the mechanism of "mental-coordinated aggregates".And the modes of interaction between SQ-1 and SQ-2 with Fe3+ have been proved by FL,1H NMR and DLS(dynamic light scattering).The experiment results indicate that the extension of the crown chain can improve the solution of the squaraine dyes and the recognition ability of SQ-1 and SQ-2 toward Fe3+.SQ-land SQ-2 shown strong fluorescence intensity in DMSO/H2O(20:80,v/v)mixed solution,upon addition of Fe3+ the fluorescence intensity drops gradually,and the color of the solution change to colorless from blue,achieving the selectivity response with Fe3+.(3)Squaraine dyes have a high tendency to aggregate in water solutions;which can fluorescence quenching.Some metal ions can complex with squaraine dye,disaggregated the monomer from aggregation,turning on the fluorescence.This process is called "mental-induced disaggregates".The new fluorescence probe SQ-3,which has realized the detection of Pb2+ based on the mechanism of "mental-induced disaggregates".The experiment results show that there is no fluorescence when SQ-3 in MeCN/H2O(90:10,v/v)solution,As the concentration of Pb2+ increased,the fluorescence intensity of SQ-3 was gradually enhanced,which has realized the selectively detection of Pb2+.And the modes of interaction between SQ-3 with Pb2+ have been proved by FL,1H NMR and DLS.The practicality of this novel fluorescent chemosensor was validated for the detection of Pb2+ concentration in urine and shrimp samples,demonstrating its advantage of simplicity,selectivity,and sensitivity.