Synthesis Of Malononitrile-type Thermally Activated Delayed Fluorescent Compounds And Their Application In OLEDs And Fluorescent Probes

TADF?thermally activated delayed fluorescence?is a luminescence phenomenon that takes advantage of the tiny energy gap between the singlet and triplet states of the fluorescent body,and achieves efficient fluorescence emission by means of reverse intersystem crossing of non-radiative triplets to radiative singlets.TADF materials are regarded as the third generation of luminescent materials after fluorescence and phosphorescence due to their unique photophysical properties such as 100%internal quantum efficiency and no need of noble metals,making it a hot topic in the research field of organic luminescent materials.In this thesis,we report the design and synthesis of thermally activated delayed fluorescence molecules with 2-?diphenylmethylene?malononitrile,namely,DPMM,as the core framework.The single crystal structure and photophysical properties of these TADF molecules were investigated and their applications in organic electroluminescent devices and fluorescent probes were studied.The detailed contents are summarized as follows:?1?Three donor-acceptor-donor type emitters containing a propeller-like scaffold 2-?diphenylmethylene?malononitrile?DPMM?as the acceptor unit and triphenylamine?TPA?/carbazole?Ph Cz?/9,9-dimethylacridine?DMAC?as the donor moiety were designed and synthesized.The three compounds exhibited excellent thermal and electrochemical stability and a significant positive solvatochromism with a remarkable redshift of the PL emission peak from the nonpolar hexane solvent to the strong-polar acetonitrile solvent.DPMM-2TPA and DPMM-2DMAC exhibited significant TADF character with an extremely small?E_ST of 0.06and 0.01 e V through efficient reverse intersystem crossing from triplet state to singlet state.As for DPMM-2Ph Cz,TADF phenomenon cannot be detected due to its large energy split between³CT and ¹CT.More importantly,highly efficient red-OLEDs based on DPMM-2TPA and DPMM-2DMAC with the maximum external quantum efficiencies of 16.5 and 12.7%,respectively,had been achieved,which was significantly higher than the average efficiency of previously reported TADF OLEDs with similar color gamut.?2?The TADF compound DPMM-2TPA was used as the recognition molecule to detection N₂H₄,and the changes of fluorescence and fluorescent life of the compound after the interaction of the malononitrile unit of DPMM with hydrazine hydrate.In DMF/PBS?10 m M,DMF:PBS=7:3,v/v,p H=7.4?buffer solution,with the change of hydrazine hydrate content,the solution color change from orange to colorless,the fluorescent color change from orange to blue and the fluorescent life alter from 1.73 to 3.61 ns.The spectral properties showed that DPMM-2TPA had anti-interference ability against other metal ions,anions and organic small molecules,and its detection limit for hydrazine hydrate was 45.22 n M?1.439 ppb?,far lower than the maximum allowable concentration?10 ppb?stipulated by the US Environmental Protection Agency.