Synthesis And Photophysical Properties Of Small Organic Molecules Based On Nitrogen/Sulfur Heterocycles

Luminescence materials have been widely concerned due to their potential applications in optoelectronic devices,anti-counterfeiting encryption,biological imaging and so on.Compared with inorganic luminescence materials,pure organic luminescence materials have the advantages of low cost,low biotoxicity,simple preparation and easy structure modification.With the development of this field,organic luminescence materials with multiple luminescence properties show unique advantages and exhibit a better application prospect.In addition,the adjustment of luminescence properties of organic luminescence materials is not limited to the change of molecular structure,but also its micro stacking form.The study of molecular conformation-stacking-property relationship will help us to understand organic luminescence materials and guide the molecular design.In this paper,DBTDO-DMAC,DBTDO-DPA,DBTDO-Cz and DBT-4-Cz were designed and synthesized.The structures of the target molecules were identified by ¹H NMR,¹³C NMR,high resolution mass spectrum and single crystal X-ray diffraction.The photophysical properties of the corresponding molecules were characterized by uv-visible absorption spectra,fluorescence spectra,phosphorescence spectra,fluorescence lifetime,phosphorescence lifetime and luminescence quantum yields.According to single crystal or powder X-ray diffraction,the stacking modes of compounds were analyzed.The relationship between stacking and properties was discussed.The main research contents are as follows:1.The research progress of fluorescence,room temperature phosphorescence（RTP）,mechanoluminescence（ML）,and mechanochromism（MC）materials was reviewed in chapter one.We focused on the relationship between molecular packing and properties,and the design of organic luminescence materials with multiple luminescence properties.Finally,the design idea of this paper was put forward.2.The D-A compound DBTDO-DMAC was designed and synthesized according to the folded or planar conformation of 9,10-dihydro-9,9-dimethylacridine.The crystal G showed a red shift from 495 nm to 530 nm after grinding with the increase of quantum yield.Crystal Y showed obvious yellow RTP.Single crystal analysis indicated that the dimer of crystal G exhibited staggered arrangement with weaker intermolecular interactions and the molecular arrangement was easy to change under the stimulation of force to produced MC properties.While the dimer of crystal Y exhibited an antiparallel stacking mode with abundant symmetric intermolecular interactions to suppress the non-radiative transition and realize RTP.In addition to the electronic properties,the regulatory role of molecular conformation in aggregates should be paid more attention.3.DBTDO-DPA and DBTDO-Cz compounds were designed and synthesized to compare with DBTDO-DMAC.Single crystal analysis shows that asymmetric interleaved stacking is conducive to the realization of MC,and effectiveπ-πstacking is benefit for the production of RTP.This work has some guidance for the design of other MC or RTP molecules.4.DBT-4-Cz was designed and synthesized by covalent bonding of two common donor units（carbazole and dibenzothiophene）.The as prepared DBT-4-Cz microcrystals exhibited weak dark blue ML.The bulk single crystal of DBT-4-Cz exhibited the thermal activation delayed fluorescence properties with the lifetime of 148 ms and obvious RTP with lifetime of 572 ms（phosphorescence quantum yield of 2.07%）.This compound realized multiple emission of fluorescence-TADF-RTP successfully,and showed blue-white luminescence under ultraviolet light with quantum yield of 21.93%.This work provides some guidance for the design of multi-luminescence materials.