Synthesis And Properties Of Resonant Thermally Actived Delayed Flerescent Materials Based On Carbazole And Diphenylamine Derivativese

The advent of Thermally Activated Delayed Fluorescence(TADF)materials has made it possible to prepare pure Organic Light-Emitting Diodes(OLEDs)with 100%internal quantum efficiency,usually by constructing structures of donor-acceptor(Donor-Acceptor(D-A)to achive the Highest Occupied Molecular Orbital(HOMO)and the Lowest Unoccupied Molecular Orbital(LUMO)are effectively separated to design molecules,thus the search for a smaller energy level difference that facilitates the crosstalk between anti-systems,converting non-luminescent trilinear excitons into single-linear excitons that can be used for luminescence.In commercial applications we can use colour filtering or optical microcavities to improve the colour purity and obtain excellent CIE,but this reduces the energy utilisation and makes the device fabrication process more complex.However,boron-nitrogen resonance-induced TADF materials(MR-TADF),which are based on boron and nitrogen atoms at specific positions in the rigid structure,can induce resonance effects,resulting in a high colour purity luminous spectrum with TADF properties.There are few MR-TADF related reports,so there is a need to further develop new resonant MR-TADF materials and prepare high colour purity OLED devices.This paper focuses on the synthesis and properties of MR-TADF materials based on carbazole and diphenylamine derivatives constructs as follows.In Chapter 2,carbazole and diphenylamine derivatives were used as the basis f or synthesizing the parent nucleus of the resonance structure,and tert-butyl dip henylamine donor was introduced at the peripheral HOMO and LUMO position s to achieve the light color coverage from deep blue light to sky blue light th rough the adjustment of the molecular structure.Subsequently,the electrolumine scent devices prepared with these three luminescent materials showed better per formance,with the maximum external quantum efficiency reaching 15.6%for t he deep blue light devices and 18.8%for the sky blue light devices,but their devices still had serious efficiency roll-off problems.In Chapter 3,to avoid the introduction of peripheral donor bodies disrupting the resonance structure while achieving a further red-shift of the luminescence wavelength.We designed and synthesised an MR-TADF material,DBNO,by employing the strategy of para-B-?-B and para-O-?-O,N-?-N to increase the donor-acceptor capacity with the concept of boron,oxygen and nitrogen embedded in polycyclic aromatic hydrocarbons.The designed molecule exhibits a vivid green emission in toluene solution with a high photoluminescence quantum yield(PLQY,96%)and an extremely narrow FWHM(19 nm),which surpasses all previously reported green TADF emitters to date and is even comparable to quantum dots.In addition,the long strip molecular structure gives a high level of emission dipole rate of 96%along the direction of the leaping dipole moment.The DBNO-based fabricated organic light-emitting diodes show narrow-band green emission with a peak at 504 nm and a FWHM of 24 nm.In particular,the device performance is greatly enhanced by the TADF-sensitisation(hyperfluorescence)mechanism with a FWHM of 27 nm,achieving a state-of-the-art maximum external quantum efficiency(EQE_max)of 37.1%and a reduced efficiency roll-off.