Synthesis Of Sulfur-containing Heterocyclic Small Molecular Light Emitting Organic Materials And Their Highly Efficient Blue And White Organic Light Devices

During the past 30 years, the field of organic photoelectric materials has expericend great development such as in the organic light emitting diodes(OLEDs), organic solar cells(OSC), optical sensors etc., and in particular organic light-emitting diodes have been successfully realized commercially application and has brought new experience to people’s life. Among the organic R, G, B three-color light-emitting materials, the efficiency and device stability of red and green materials are very good, but blue material is relatively inferior. Thus the paper focuses on the blue light emitting materials and its performance, which includes traditional fluorescent materials and thermally activated delayed fluorescence(TADF) material.In chapter 2, a series of blue emitters incorporating spiro-[fluorene-9,9′-thioxanthene] or spiro[fluorene-9,9′-thioxanthene-S,S-dioxide] as the core and phenylcarbazole or triphenylamine as the arms were designed and synthesized. Their spiro conformation is beneficial for their thermal stability and for reducing the trend of aggregation quenching. By tuning the valence of the sulfur atom, highly efficient local excited(LE) state deep blue emitters and charge-transfer(CT) state blue emitters are obtained. The devices based on the LE emitters TPA-S and CzB-S as the nondoped emissive layer exhibit high external quantum efficiency of 1.76% and 2.03% and Commission Internationale de l’Eclairage(CIE) coordinates of(0.158, 0.039) and(0.160, 0.054), respectively, and their CIEy values are among the smallest ever reported for the deep blue OLEDs and are readily very close to that of the inorganic light-emitting diode [CIE(0.16, 0.02)]. The nondoped device based on the CT emitter TPA-SO2 as the emissive layer also exhibits a high current efficiency of 5.46 cd/A and CIE coordinates of(0.154, 0.168). To fully utilize the 25% singlet and 75% triplet excitons, fluorescent/phosphorescent hybrid white organic light-emitting diodes in a single-emissive-layer architecture were also fabricated with TPA-SO2 as the blue emitter as well as the host of orange phosphorescent emitter to give forward-viewing power efficiency of 47.9 lm/W, which is the highest value ever reported for the devices in a similar architecture without using any out-coupling technology.In chapter 3, two novel bipolar isomeric blue fluorophores, PPI-TPA-SO2-1 and PPI-TPA-SO2-2, consisting of electron-withdrawing phenanthro[9,10-d]imidazole and sulfone-locked electron-donating triphenylamine, were designed and synthesized. The sulfone lock induces a more twisted molecular conformation, and thus a higher triplet energy level and better triplet exciton confining ability compared with the analogue TPA-PPI without the sulfone lock. In addition, the introduced sulfone lock also offers the developed materials improved electron affinities and an electron dominant transporting ability. They were utilized as the blue emitter and the host for a yellow phosphorescent emitter to fabricate fluorescence–phosphorescence(F–P) hybrid white organic light-emitting diodes(WOLEDs) in a single-emissive-layer architecture, giving forward-viewing maximum current efficiencies of 44.2 and 47.6 cd/A, power efficiencies of 49.5 and 53.4lm/W, and external quantum efficiencies of 14.4% and 15.6%, respectively, which are much higher than those of the devices based on TPA-PPI(29.5 cd/A, 33.1lm/W, and 9.6%) due to their superior singlet and triplet exciton separation and utilization ability over TPA-PPI. These efficiencies are also the highest values ever reported for the F–P hybrid WOLEDs in a similar architecture, and their power efficiencies are even comparable with most reported highly efficient all phosphorescent WOLEDs without using any out-coupling technology.In chapter 4, two thioxanthone derived isomeric series thermally activated delayed fluorescence(TADF) emitters 1,6-2TPA-TX/3,6-2TPA-TX and 1,6-2TPA-TXO/3,6-2TPA-TXO with the same electron acceptor and electron donor but different donor combining strategy are developed for organic light-emitting diodes. The emitters 3,6-2TPA-TX and 3,6-2TPA-TXO with symmetrical configuration and relieved twisted dihedral angle between the donor and acceptor could possess an acceptable singlet-triplet splitting energy(ΔEST) as well as a large photoluminescence quantum yield. Blue emission TADF devices based on 3,6-2TPA-TX realized an extremely high maximum external quantum efficiency(EQE) of 23.7%. In addition, a unprecedented ever high maximum EQE of 24.3% was achieved for yellow emission TADF devices based on 3,6-2TPA-TXO by solely changing the sulfur atom valence state of the thioxanthone core. On the contrary, their corresponding asymmetric isomers are dominated by more severe non-radiative deactivation pathway to give much low EQE values(<5%). By utilizing 3,6-2TPA-TX as a blue emitter and 3,6-2TPA-TXO as a yellow emitter, ever highest EQE of 20.4% could be achieved for all fluorescence white organic light-emitting diodes.