?-Conjugated Structure Enhanced Ultraviolet Absorption And Fluorescence And Its Analytical Application

The ?-conjugated structure has become a research hotspot of photofunctional nanomaterials due to its large ?-electron delocalization,structural modification and excellent light responsiveness.This kind of materials are widely used in optical therapy,fluorescence imaging,ophotocatalytic reactions,optoelectronic devices and other fields.In this paper,the effects of ?-conjugate structure on the optical properties of organic molecules and inorganic nanomaterials are studied,and the mechanism of optical properties enhancement is discussed.This property is applied to the development of nitrite high sensitivity UV-visible absorption spectrophotometry and the preparation of gold nanocluster materials with excellent properties.This study clarifies the regulatory mechanism of the introduction of ?-conjugate structures to the optical properties of organic molecules and inorganic nanomaterials,and provides a theoretical basis for the further development of functional inorganic and organic materials with excellent properties.The research content of this thesis is as follows:1.The non-conjugated thiol(glutathione)and the ?-conjugated thiol(2-thiobarbituric acid)are reacted with nitrite under acidic conditions to produce S-nitro thiol compounds(RSNO),and have a absorption peak in the UV range(320-360 nm).It is found that the RSNO containing?-conjugate structure have greater absorbance by ultraviolet-visible spectrophotometry.The experimental data and mechanism prove that the existence of ?-conjugate structure reduces the energy gap value of electron transition,reduces the way of electron transition,improves the electron transition efficiency and makes the ?-conjugate structure thiolate have a high molar absorption coefficient,and then improves the sensitivity of ultraviolet-visible spectrophotometry to detect nitrite.It is proved that the existence of ?-conjugated structure reduces the band gap value and reduces the pathway of electronic transition by experimental data and theory,so that the ?-conjugated thiolate has a higher molar absorption coefficient,and then improves the sensitivity of ultraviolet-visible spectrophotometry to detect nitrite.In addition,non-conjugate structure thiol(tiopronin)and ?-conjugate structure thiol(4-amino-6-hydroxy-2-mercaptopyrimidine monohydrate)were introduced into nitrite,respectively,and it was found that the ?-conjugate structure thiol could improve the molar absorption coefficient of RSNO,and the universality of the method was verified.By comparing the linear range of nitrite and the detection limit by four kinds of thiol molecules,it is concluded that the detection of nitrite by ?-conjugated thiol(2-thiamine barbiturates)has low detection limit and high sensitivity.2.The ?-conjugated structure is used to improve the optical performance of inorganic nanomaterials.Taking gold nanoclusters as a case study,the surface ligand of using non-conjugated thiol(glutathione)and ?-conjugated thiol(4-amino-6-hydroxy-2-mercaptopyrimidine monohydrate)with gold nanocluster has a great influence on its luminescence performance.At pH=3,it was found that the fluorescence intensity of ?-conjugate thiol gold nanoclusters was much higher than that of non-conjugated thiol gold nanoclusters.Experimental data and calculations show that the?-conjugate hydrogen bond aggregation enhancement fluorescence.At the same time,the use of non-conjugated thiol(tiopronin)and ?-conjugate thiol(2-thioxanthine)was used to verify the universality of ?-conjugate hydrogen bond aggregation enhancement fluorescence.The ?-conjugate hydrogen bond aggregation results in a limited rotation of the ligand on the gold surface,reducing the non-radiation transition,resulting in a longer fluorescencelife and a higher quantum yield.In addition,the gold nanocluster aggregates can maintain high fluorescence intensity in a wide pH range after heat treatment,which lays a good foundation for its further application in biochemistry and catalysis.