Synthesis And Properties Of Nitrogencontaining Condensed Heterocyclic Organic Small Molecule Fluorescent Compounds

The nitrogen-containing fused heterocyclic organic small molecules are widely used in medicine,dyes,pesticides,optoelectronic materials and other fields.As a fluorescent molecule,research on fluorescent probes,fluorescent dyes,and fluorescent materials has achieved many results.However,most compounds have complex structures,difficult synthesis and limited applications.So it is still of great significance to construct fluorescent molecules with long wavelength emission and high luminous efficiency.In this thesis,three series of small molecule fluorescent compounds were designed and synthesized around the structure of nitrogen heterocycles,and their fluorescence properties were studied in detail.The first part used 2-benzoylpyridine,substituted salicylaldehyde and ammonium acetate as raw materials.Four imidazo[1,5-a]pyridines 2-2 were synthesized by a three-component one-pot reaction,its yield was 49%～77%.Based on this,four corresponding N,O-fluoroboron complexes 2-3 were formed by complexing with boron trifluoride ether,and the yield was 30%～79%.Precursor compound 2-2 and fluoroboron complex2-3 have good fluorescence emission both in solvent and solid state,and have a large Stokes shift（up to 213 nm）in the solvent.The introduction of an electron-withdrawing group causes a red shift in the fluorescence emission wavelength of the compound,and the introduction of an electron-withdrawing group causes the fluorescence to be almost quenched.The fluorescence intensity of compound 2-2c will be significantly enhanced under significantly acidic conditions and it exhibits green fluorescence quenching after introducing Cu²⁺in Me CN/H₂O mixed solution.Which can be used as a“Turn-Off”type fluorescent probe that specifically recognizes Cu²⁺.Finally,the structures of compounds 2-2a～2-2d and 2-3a～2-3d were optimized by DFT calculation,and the test results were verified by TD-DFT calculation.In the second part,three 2-amino-1,3,4-thiadiazolyl coumarin compounds 3-3were synthesized using substituted coumarin carboxylic acid and aminothiourea as raw materials.The yield was between 57%and 85%.After reacting with the substituted benzoyl chloride,three corresponding amide derivatives 3-4 were produced,and the yield was 86%～92%.Based on this,three corresponding N,O-fluoroboron complexes3-5 were formed by complexing with boron trifluoride ether,and the yield was56%～70%.A total of 9 compounds in these three categories all have high fluorescence quantum yields（up to 0.95）.Compound 3-4c has a red-shifted fluorescence emission wavelength under alkaline conditions and can be used as an acid-base p H probe.The introduction of Fe²⁺into the Et OH/H₂O mixed solution of compound 3-4c can greatly reduce the fluorescence intensity,and it can be used as a fluorescent probe that specifically recognizes Fe²⁺.Compound 3-5c has strong fluorescence in non-polar solvents,but almost quenches the fluorescence in polar solvents.In addition,its fluorescence gradually increases under alkaline conditions.So it can be used as a p H probe under alkaline conditions.Finally,the structures of compounds 3-4a～3-4c and 3-5a～3-5c were optimized by DFT calculation,and the test results were verified by TD-DFT calculation.The third part uses coumarin as the direct raw material,or uses substituted salicylaldehyde and ethyl acetoacetate as raw materials to synthesize 3-acetyl coumarin compounds,which are then brominated to produce the corresponding 3-（2-bromo Acetyl）coumarin.Then reacted with thioamide compounds to synthesize 9 3-thiazolyl coumarin compounds 4-5,and the yield was 49%～87%.The fluorescence of these compounds is greatly affected by the solvent and the substituent.The Stokes shifts of compounds 4-5a～4-5c are very large,generally above 200 nm.The diethylamine-substituted compounds 4-5g～4-5i have higher fluorescence quantum yields（about0.40）.It was found that compounds 4-5a,4-5b,and 4-5c all exhibit different fluorescence responses under different p H conditions,and they can be used as p H-type fluorescent probes.Compounds 4-5a～4-5c have good solid fluorescence,among which the solid fluorescence quantum yield of 4-5b reaches 0.30.Finally,the structure of compounds 4-5a～4-5c was optimized by DFT calculation,and the test results were verified by TD-DFT calculation.