Manipulating The Photoelectric Properties Of Iridium(Ⅲ) Complexes:Material Design And Device Fabrication

Recently, organic light-emitting diodes(OLEDs) offer an intriguing future for the next generation of flat-panel displays and lighting techniques because of their low energy consumption, wide viewing angle and flexible display, etc. Among many luminescent materials used for OLEDs, iridium(III) complexes are drawing extensive attention due to their high luminescence efficiencies, good photo-thermal stability and easy tunability of emission wavelength. Nevertheless, like other luminescent materials, iridium(III) complexes suffer from the concentration self-quenching effect in the operation process of devices, which impedes their performance improvement and application in OLEDs. Moreover, most OLEDs based on iridium(III) complexes are usually faced with serious efficiency roll-off and color drift problems. Therefore, it is indispensable and important to make further investigations on the structure and property of iridium(III) complexes for obtaining excellent luminescent materials and improving their application value in OLEDs.In this dissertation, we designed and synthesized a series of novel iridium(III) complexes via adopting different cyclometalated and ancillary ligands. OLEDs exhibiting favorable performance based on them have been successfully fabricated through manipulating their luminescent properties. The relative studies are outlined as follows:(1) The design and synthesis of blue iridium(III) complexes based on phenyl-triazole ligands and manipulation of their photoelectric properties. With the help of quantum chemical calculations, the phenyl-triazole derivatives were selected here as the cyclometalated ligands and pyridyl-pyrazol derivatives were used as the ancillary ligands to construct target molecules. A series of novel blue iridium(III) complexes with different degrees of steric hindrance were subsequently prepared through introducing methyl and propyl groups. The photoluminescence and electroluminescence properties were systematically studied. The experimental results indicated that the introduction of propyl groups into the cyclometalated ligands was probably beneficial to reducing the concentration self-quenching effect, thus increasing the photoluminescence quantum yields(PLQYs) in neat films and electroluminescence(EL) efficiencies.(2) The synthesis of green cationic iridium(III) complexes with different degrees of steric hindrance and the regulation of their photoelectric properties. The carbazole was employed as hindrance moiety and introduced into the cyclometalated ligand 1,2-diphenyl-1H-benzoimidazole(Hpbi) to prepare green cationic iridium(III) complexes showing different degrees of steric hindrance. The photophysical experiment results suggested that the introduction of carbazole group was effective to enhance their PLQYs in neat films. In view of their crystal structures, it was tentatively speculated that carbazole moieties could help separate the emissive cores from each other in the cationic iridium(III) complex and depress self-quenching problems as a result.(3) Synthesis of highly efficient green iridium(III) complexes were and fabrication of favorable OLEDs possessing stable efficiency. The Hpbi was selected as a cyclometalated ligand together with pyridyl-triazole and pyridyl-benzimidazole derivatives as the ancillary ligands to prepare novel green neutral iridium(III) complexes. The obtained OLEDs adopting these iridium(III) complexes as the guest materials displayed high efficiencies with a peak current efficiency(ηc) of 45.0 cd A–1 and power efficiency(ηp) of 47.9 lm W–1. More encouragingly, little efficiency roll-off values upon increasing the brightness were observed in their doped OLEDs, which still retained high efficiencies of 44.5 cd A–1 and 31.5 lm W–1 at 1000 cd m–2.(4) The design and synthesis of green iridium(III) complexes with promising luminescent properties as well as fabrication of high quality non-doped OLEDs. The Hpbi presented here was used as a cyclometalated ligand together with pyridyl-triazole and pyridyl-benzimidazole derivatives as the ancillary ligands to obtain four green iridium(III) complexes. These complexes displayed strong emissions with high PLQYs of 70–92% in CH2Cl2 at 298 K. Non-doped OLEDs using the complexes as emitters possessed outstanding performance with a maximum ηc of 19.8 cd A–1 and ηp of 20.4 lm W–1 whilst simultaneously displaying low efficiency roll-off at high luminance.(5) Synthesis of novel orange iridium(III) complex for fabricating of high-performance white OLED(WOLED). Through expanding the conjugation degree of molecular system, an orange iridium(III) complex using Hpbi as the cyclometalated ligand was designed and synthesized. The orange complex was effectively available to combine with the traditional blue-emitting material(FIr6) for successfully fabricating high quality two-element WOLED. The resultant WOLED showed a peak ηc of 22.1 cd A–1 and ηp of 25.5 lm W–1, simultaneously possessing favorable color rendering index(CRI) of 80. Especially, this WOLED displayed qualified R9 of 13 and Duv of –0.0013, which conformed to the required standard for lamp illumination of the ENERGY STAR and Commission Internationale de L′Eclairage(CIE).