Synthesis And Characterization Of OLEDs Dopants Based On Platinum(?) And Thermally Activated Delayed Fluorescence Complexes

The development of organic light emitting diodes(OLEDs)materials play an important role in the progress of OLEDs technology.Many attentions have been focused on the emissive materials during the research of OLEDs materials.Since the invention of OLEDs in 1987,the OLEDs materials have achieved great progress.The emissive materials have been developed rapidly from first-generation organic fluorescent compounds to second-generation heavy-metal-complex-based phosphorescent molecules and furtherly to third-generation thermally activated delayed fluorescent(TADF)compounds.Compared with the conventional fluorescent compounds,phosphorescent metal complexes can harvest both singlet and triplet excitons through the spin-orbital coupling via metal ions,theoretically achieving a 100% internal quantum yield.Since TADF materials have small singlet-triplet splitting energy,it can efficiently harvest triplet excitons by taking the advantage of reverse intersystem crossing(RISC)from the lowest triplet(T1)excited state to the lowest singlet(S1)excited state.It can also achieve a 100% internal quantum yield in theory.At present,the highly efficient and stable blue emissive OLEDs materials are highly desirable,and they can be considered as the bottleneck to the development of OLEDs technology.Therefore,the exploitation of new efficient and stable blue OLEDs materials are particularly imperative.In this thesis,our work mainly focuses on the study of blue emitting materials(phosphorescent and TADF materials).In the first part of the work,three emitting Pt(II)complexes(Pt1,Pt2 and Pt3)composed by imidazo[1,2-f]phenanthridine-containing tetradentate ligands have been designed and prepared.Because of this imidazo[1,2-f]phenanthridine unit have strong rigidity and high triplet energy(ET),it is suitable for the preparation of blue-emitting complexes.At the same time,the introduction of heteroatom linkage and spiro linkage into these Pt(II)complexes would be effective in breaking the conjugation,leading the wide bandgap and high ET.Furthermore,bulky mesityl group was attached to the reactive 3-position of imidazo[1,2-f]phenanthridine to reduce the strong intermolecular interaction under electric-excitation condition and increase the solubility of resulting complexes.Organic light-emitting diodes(OLEDs)based on these three guest complexes were fabricated.Among these three Pt(II)complexes,Pt1 showed the highest OLEDs performance with the maximum CE,PE,and EQE of 36.5 cd A-1,33.1 lm W-1,and 16.2%,respectively,which was comparable to the best sky-blue Pt(II)-based emitters.In addition,all these three OLEDs devices exhibited excellent spectral stability in different doping ratio.In the second part of the work,we designed and synthesized three blue TADF materials Cy-2Cz,Cy-3Cz and Sf-3Cz by tuning the donor units and the acceptor units.In this work,highly twisted structures are applied in Cy-2Cz and Cy-3Cz to separate the highest occupied molecular orbitals(HOMOs)and lowest unoccupied molecular orbitals(LUMOs),where the ?EST is reduced by using biphenyl as a twisting unit between the donor and the acceptor.Within Sf-3Cz,we used high-triplet-energy carbazole units as the donor part,and a typical TADF acceptor(sulfone)as the electron-withdrawing part.All these three molecules have high triplet energy levels and small ?ESTs.Organic lightemitting diodes(OLEDs)based on these TADF guests were fabricated.The deep blue OLEDs based on the Cy-2Cz and Sf-3Cz exhibited high device performance,the maximum current efficiency are(11.8 cd A-1,19.2 cd A-1)and the maximum external quantum efficiency are(11.9%,15.8%)respectively.