Research On Synthesis And Photophysical Properties Of Imidazoles With Mechanofluorochromism

Mechanofluorochromic（MFC）is a dynamic optical phenomenon which the wavelength or intensity of fluorescence changes under the force.Small organic molecules with MFC properties have been applied in security ink,information storage,biological imaging and other fields.The synthesis of small molecules and constructing strategies of their fluorescence properties have become a significant field recently.In this paper,imidazoles with different number groups and group isomerization was designed and synthesized.The photophysical properties of compounds in solution and solid state have been studied,and the mechanism of their MFC activity has been investigated.The main contents are as follows:1.A series of 1,2,4,5-tetrarylimidazole compounds（IMV0-V3DMA）with different amounts of vinyl have been synthesized and the effect of the number of vinyl groups on the fluorescence properties of IMV0-V3DMA compounds has been studied.It was found that IMV0-V3DMA showed positive solvochromic fluorescence emission in the solution state,and the emission wavelength gradually red-shifted with the increase of solvent polarity,but the emission intensity of IMV0-V3DMA decreased with the increasing number of vinyl.In the solid state,IMV0-V3DMA showed dynamic and reversible MFC activity,but the corresponding MFC activity decreased with the increasing number of vinyl groups.The increase of the moment of inertia of the electron-donating group on the N₁-phenyl group of imidazole might be responsible for the decrease of compound MFC activity.The results of XRD and DSC showed that the force-induced morphologic transformation is responsible for the reversible MFC activity of IMV0-V3DMA.2.The imidazole groups were introduced into C₃or N₉atoms of phenothiazine（PTZ）,IMC-PTZ and IMN-PTZ linked isomers were synthesized.The fluorescence properties of IMN-PTZ showed that there was a nearly vertical dihedral angle between PTZ and N₁-phenyl on the imidazole nucleus.The partialπconjugation of PTZ with imidazole is severely hindered,and the emission of the compound in solution and crystal is very weak.However,the dihedral angle between PTZ and N₁-phenyl on imidazole nucleus was small in IMC-PTZ,and the fluorophore produced strong emission in solution and crystal.The results of XRD and DSC showed that the force-induced morphologic transformation were responsible for the compounds MFC activity.The red-shifted emission of IMN-PTZ is larger than that of IMC-PTZ stimulated by force.It was confirmed that the intense intermolecular interaction of the compound in IMN-PTZ crystals was responsible for the significant red-shifted emission in solution and crystal state.3.BIM_NPYand BIM_CPYwere synthesized by using pyrene group as electron-donating group and 4-cyanophenyl group as electron-withdrawing group.The BIM_NPYexhibits positive solvent effect in solution,but the emission wavelength of the BIM_CPYis not sensitive to solvent polarity.The fluorescence colors of the crystal compounds are blue and cyan green,respectively.The fluorescence wavelengths of the compounds blue-shifted after stress,and become blue and cyan blue after liquid nitrogen quenching,respectively.The fluorescence of the BIM_NPYcan recover under solvent fumigation or hot annealing,while the BIM_CPYdoes not recover.The results of XRD and DSC show that dichloromethanes which is involved in the formation of eutectic compounds due to the molecular stacking of BIM_CPY.The molecular stacking of BIM_CPYis destroyed under force,and the emission wavelength of BIM_CPYis difficult to recover to the crystal phase state under the condition of fumigation and annealing.Combined with the theoretical calculation results,the MFC mechanism of the larger plane modified groups based imidazole derivatives was declared from the perspective of molecular stacking.