Mechanofluorochromic Properties Of Salicylaldehyde Hydrazone Derivatives

Organic photochromic materials have developed rapidly in recent years,and have great application in fluorescence tracking reagents,organic light-emitting diodes,stress detection,anti-counterfeiting and encryption,and biological cell imaging.Mechanofluorochromic materials（MFC）is a new type of stimulus-responsive material that has emerged in recent years.The most important point for developing MFC dyes was to design D-π-A fluorescent dyes,which were controlled by tuning the electron-donating ability of D,electron accepting ability of A,and the space size of theπbridge unit.D-π-A conjugated compounds with AIE activity usually had strong twisted skeletons and showed intramolecular charge transfer（ICT）.And the structure can be easily destroyed under external force stimulation,resulting in MFC phenomenon.Organoboron complexes have developed into an important molecular system in the field of stimulus-responsive functional materials due to their unique photochemical and photophysical properties.Summarizing the development of mechanofluorochromic materials,it is not difficult to see that in the future,the construction of MFC molecules with simple structure,easy-synthesis,and strong contrast will become the mainstream of research.Therefore,the design and synthesis of fluorescent materials with strong contrast.In this paper,we designed and synthesized a salicylaldehyde acylhydrazone derivative DHBH and two salicylaldehyde organoboron compounds DPDP and DPDN with AIE activity,and studied their aggregation-induced luminescence characteristics and（MFC）properties,respectively,and the recognition performance of the fluorescent probe DHBH for Al³⁺.The specific content is as follows:Chapter 1:We mainly summarized the development status and influencing factors of mechanofluorochromic materials in recent years,briefly introduced acylhydrazone derivatives,and summarizes the fluorescent color changing properties of salicylaldehyde acylhydrazone derivatives.The recognition performance of fluorescent probes for ions and the fluorescence characteristics of organoboron compounds were also discussed.Finally,the main research content and research significance of this thesis are summarized.Chapter 2:A simple salicylaldehyde hydrazone derivative DHBH with AIE activity was designed and synthesized,which had reversible force-induced fluorescence color change properties.The molecular conformation and stacking mode of DHBH will cause changes in its optical properties under external stimulation.Powder X-ray diffraction（PXRD）and single crystal test results showed that the MFC characteristics of compound DHBH were caused by the reversible phase transition from its crystalline state to the amorphous state.In addition,the compound DHBH showed good selectivity for Al³⁺.Chapter 3:Two new salicylaldehyde hydrazide organoboron complexes DPDP and DPDN with AIE activity were designed and synthesized.The research results showed that both of them exhibited reversible MFC behavior.This phenomenon can be easily switched multiple times through the grinding-fumigation process without fatigue.The results of powder X-ray diffraction（PXRD）and field emission scanning electron microscopy（FESEM）further showed that the MFC behavior of the compounds DPDP and DPDN resulted from the transition between the crystalline and amorphous states under external stimuli.