| Y-shaped imidazole derivatives has attracted much attention because of its excellent nonlinear optical properties.This type of imidazoles was formed by introducing an aromatic system at the 2,4,5-position of the imidazole ring to form a large conjugation system,the luminescence properties are adjusted by different substituents,and there is a greater application prospect in fluorescent sensors and the like.Based on the research of our group of Y-type imidazole derivatives,28 kinds of unreported 2,4,5-tris（4-substituted styryl）imidazoles and 3 kinds of 2-（4-substituted phenyl）-4,5-di（4-substituted styryl）imidazoles were synthesized using 2,3-butanedione,4-substituted benzaldehyde,4-substituted cinnamaldehyde and ammonium acetate as the main raw materials.Five 2-（4-substituted phenyl）-4,5-bi（4-substituted phenyl）imidazoles was synthesizedviathefunctionalgroupstransformationof2-（4-substituted phenyl）-4,5-di（4-substituted styryl）imidazoles.Studied the optical properties of the above compounds,the contents are as follows:（1）Four different substituents of 1,6-bis（4-substituted phenyl）-1,5-hexadiene-3,4-dione（MTones）were synthesized using 2,3-butanedione and 4-substituted benzaldehyde as raw materials by the Claisen-Schmidt reaction.When the methanol solution of 2,3-butanedione was added dropwise to the reaction flask within 4 hours,the yield increased by more than 4%.The structure of these compounds was characterized by FTIR、1H NMR and 13C NMR.The UV absorption properties were investigated by UV absorption spectrum.The molar absorptivity was more than 1.9×104 L?mol-1?cm-1.（2）Based on 2-（4-bromophenyl）-4,5-bis（4-methoxystyryl）imidazole,2-（4-bromophenyl）-4,5-bis（4-hydroxystyryl）imidazole（2a）was synthesized by demethylation reaction.The structure of these imidazoles was characterized by FTIR,1H NMR and 13C NMR.The UV absorption spectrum showed no significant change in UV absorption properties.Fluorescence spectrum showed that the fluorescence intensity was significantly enhanced and a"double"fluorescence emission peak was formed.Using quinine sulfate as a standard reference,the relative fluorescence quantum yield of the compound was measured,which was 20.0%higher than before and the light-emitting efficiency was higher.（3）On the basis of 2-（4-formylphenyl）-4,5-di（4-substituted styryl）imidazole,4 kinds of2-（4-thiosemicarbazone phenyl）-4,5-di（4-substituted styryl）imidazoles（2b-2e）was synthesized by introducing thiosemicarbazide derivatives,which structure was characterized by FTIR,1H NMR and 13C NMR,and the UV was investigated.The above four compounds have ultraviolet absorption properties,the maximum absorption wavelength was about 385nm,the molar absorption coefficient was greater than 5.5×104 L?mol-1?cm-1,and the UV absorption performance is better.The fluorescence spectrum of the compound was analyzed using a fluorescence spectrometer.The emission wavelength of all the compounds was above495 nm,and the converted compound had a longer fluorescence emission wavelength and a larger Stokes shift.The relative fluorescence quantum yield of the compound was measured with quinine sulfate as the standard reference.The fluorescence quantum yield before conversion was only about 5.0%,and the fluorescence quantum yield of the compound after conversion was above 17.0%.The compound emits light more efficiently.（4）28 kinds of unreported 2,4,5-tris（4-substituted styryl）imidazoles were synthesized using MTones,4-substituted cinnamaldehyde and ammonium acetate as raw materials by modified Debus reaction.The structure of all the above compounds was proved using FTIR,1H NMR and 13C NMR.UV absorption properties of the above 28 compounds were investigated by UV.The maximum absorption wavelength of all compounds was above 380nm,and the molar absorption coefficient was greater than 2.0×104 L?mol-1?cm-1.The synthesized compound has strong absorption ability to ultraviolet light.（5）The fluorescence spectra of these imidazoles were measured by using a fluorescence spectrometer.The fluorescence excitation wavelength of all the compounds was about 380nm,the fluorescence emission wavelength was above 480 nm,the Stokes shift was above 85nm,and the highest was 125 nm.When the imidazole ring was attached to the 2-position phenyl ring substituent is strongly electron-withdrawing,the Stokes shift could be increased.（6）The relative fluorescence quantum yields of all compounds were measured with quinine sulfate as the standard.Except for the 2-position phenyl ring substituent of the imidazole ring was-NO2,the fluorescence quantum yields of other compounds were all greater than 30.0%.The quantum yield of the compound with-NO2 substituted at the2-position of the imidazole ring is only about 14.0%,and the strong electron-withdrawing groups at the 2-position of the phenyl ring substituent of the imidazole ring would reduce the luminescenceeffectivenessofthecompounds.Therefore,choosingsuitable electron-withdrawing groups as the 2-position phenyl ring substituents of the imidazole ring can make imidazole compounds have both large Stokes and good fluorescent luminous efficiency. |
