Aggregation-induced Emission And Mechanofluorochromic Properties Of The Cruciform Conjugated Molecules

The piezochromic color-changing material is a new type of"smart"stimuli-responsive material.This material has very important application value in high-tech fields such as pressure sensors,memory devices,safety inks and optical recording.Recent research results show that rigid?-conjugated cross-shaped fluorescent dyes have unique molecular structure and fascinating optical properties.Recent research results show that rigid?-conjugated cross-shaped fluorescent dyes have unique molecular structure and fascinating optical properties.Therefore,a series of cruciform conjugated fluorescent dyes with benzene ring as the core modified by carbazole,tetrastyrene and triphenylamine were prepared based on the cross-shaped fluorochromic molecules with AIE properties of D-A structure.Their intramolecular charge transfer?ICT?,AIE and MFC properties were investigated.The results of the research obtained are as follows:?1?The compounds DHCS-BC,DMCS-BC and DTCS-BC containing the D-A cross structure with large tert-butylcarbazole units were designed and synthesized,and their ICT emission,AIE behavior and pressure-induced fluorescence discoloration properties were studied.The results showed that the three compounds exhibited significant AIE behavior(?_AIE=9,19 and>492),high solid-state luminous efficiency?0.332,0.425 and 0.492?and reversible high-contrast mechanofluorochromism.The initial powders of DHCS-BC,DMCS-BC and DTCS-BC are capable of emitting bright blue-green?485 nm?,bright blue-green?479 nm?and bright yellow?526 nm?fluorescence,respectively.It is light yellow-green?524 nm?,yellow-green?534 nm?,and orange-red?606 nm?.It is worth noting that the AIE and MFC recoloring activity of the three compounds are identical,that is DHCS-BC<DMCS-BC<DTCS-BC,which is a molecular space generated by the steric hindrance of the substituents on the benzene ring around the molecule.The degree of distortion of the conformation is consistent and exhibits significant substituent dependence.?2?The compounds DHCS-TPE and DMCS-TPE with D-A cross structure were designed and synthesized.The study found that the two cross-shaped dyes exhibited unique ICT emission,significant AIE behavior and strong solid-state luminescence.More interestingly,these two compounds possess a chemiluminescent discoloration behavior that is dependent on the substituent.The steric hindrance created by the four meta-methoxy groups located on the peripheral benzene ring of the DMCS-TPE molecule gives the molecule a more distorted spatial conformation,which in turn exhibits a high contrast chemiluminescence behavior.the solid-state fluorescent color of DMCS-TPE can be effectively switched between the cyan?474 nm?of the initial powder and the yellow?531 nm?of the ground powder.However,DHCS-TPE with relatively poor molecular distortion does not exhibit pressure-induced fluorescence discoloration.This is because the strong intermolecular force of DHCS-TPE and the close packing of molecules make it impossible for external force to destroy its crystal lattice,that is,external force.Stimulation does not cause changes in its solid state fluorescence.?3?Two twisted?-conjugated molecules MDCS-TPA and FMDCS-TPA were designed and synthesized.Studies have shown that both MDCS-TPA and FMDCS-TPA have highly distorted molecular conformation,unique ICT emission properties,typical AIE behavior and high contrast chemiluminescence.under the external force stimulation,the fluorescence color of these two molecules changed from the initial bright green and bright yellow-green to the final yellow and orange,respectively,and their spectral shifts reached 51 nm and 47 nm,respectively.Moreover,the spectral properties and morphology of MDCS-TPA and FMDCS-TPA show good reversibility through grinding-heating or grinding-fumigation processes.The chemiluminescent behavior of these two compounds is attributed to the phase transition between the crystalline and amorphous forms of the molecule.The large spectral red shift produced after milling is derived from the extension of the molecular conjugation length and the subsequent PICT process.