Design,Synthesis,and Properties Of Stimuli-Responsive Organic Fluorescent And Room Temperature Phosphorescent Materials

Stimuli-responsive organic light-emitting materials have received widespread attention because of their potential applications in bioimaging,anti-counterfeiting and sensing.The materials usually change in the way molecules are stacked or their spatial configuration in response to external stimuli,thus exhibiting changes in luminescent colour（wavelength）or luminescent intensity,which can achieve dynamic anti-counterfeiting.This thesis firstly targets mechanically force-responsive organic fluorescent dyes and proposes a design strategy for this class;secondly,the supramolecular self-assembly behaviour of non-classical organic gels with rigid conjugated structures was investigated;finally,some attempts were made in the design of organic phosphorescent materials.Details of the research are as follows:Chapter 1: The mechanism of fluorescence and phosphorescence phenomenon generation;the more common kinds of stimulus response behavior of luminescent materials and stimulus response fluorescent materials and room temperature phosphorescence materials application research are reviewed.Chapter 2: Based on the fact that polymorphic molecules are usually able to exhibit reversible force-changing properties.Therefore,polymorph predictions were used to calculate the possible crystalline forms of two D-π-A molecules（named DNV-I and MBAV-I,respectively）with the same electron donor but different electron acceptors.The theoretical calculations show that the molecules with dicyanomethyl as acceptor may crystallise in different polycrystalline forms,with strong intermolecular π-π interactions in some crystalline forms,while no π-π stacking is found in some crystalline forms.In particular,three crystals with large differences in emission wavelengths were obtained by incubation of the crystal structure of compound DNV-I,and the crystal structure agreed well with the predicted results.Monomer and π-molecule clusters can be reversibly transformed by external stimuli to achieve high-contrast trichromatic force chromogenic properties.Furthermore,the force-chromic properties are temperature dependent,showing changes in emission in response to both force and thermal stimuli.This work provides an effective strategy for the development of highcontrast force-changing molecules.Chapter 3: Based on literature research,aromatic heterocycles can be used to build AIEtype molecules instead of benzene ring bridges in the bis-cyano-vinyl skeleton;in addition,the bis-cyano-vinyl structure facilitates further gelation.Based on the above characteristics,this chapter therefore designs and synthesizes an organogel with AIE properties was named MPTN,by introducing a cyclic compound thiophene containing S atoms as a fluorophore and using π-π interactions in the system as the main driving force,and the gelant responds well to ethylenediamine.Chapter 4: In this chapter,a β-diketone boron difluoride（BF₂-tPMO）compound without heavy atoms was designed and synthesised by the ’one-pot method’.The β-diketone-based boron difluoride dye with room temperature phosphorescence（RTP）is further promoted by the introduction of two benzene rings with multiple methoxy groups in the β-diketone-boron difluoride backbone,as the introduction of sp3 oxygen-bridged electron donors may enhance the triplet state activity and further promote spin-orbit coupling.In addition,the oxygen atoms in the multiple methoxy units may interact with hydrogen,boron and fluorine atoms in other molecules,thus promoting tight molecular stacking to establish a rigid environment to suppress non-radiative relaxation through vibrational stretching and external bursting.The compound has been shown experimentally to have RTP and thermally delayed fluorescence（TADF）properties suitable for security inks printed on large areas and for applications in anticounterfeiting.Chapter 5: This chapter summarized the content of the work during the postgraduate period,synthesized and studied fluorescent materials with obvious response properties to external stimuli and phosphorescent materials with room temperature phosphorescent properties,this work provides design ideas for both research directions,in addition to an outlook on the current research on the subject.