Several phosphorescent Ir III ppy-type complexes (ppy ¼ 2-phenylpyridine anion) bearing dimesitylboron (B(Mes) 2 ) units have been designed and some of them have been newly prepared. By changing the substitution positions with different electronic characters that can manipulate the electron-accepting ability of the attached B(Mes) 2 moieties, the direction of the metal-to-ligand charge transfer (MLCT) process for these Ir III complexes can be either retained or shifted, which can provide a new strategy toward phosphorescent color tuning. Through computational studies, shifting the substitution position of the B(Mes) 2 moiety on the organic ligand, some electronic features, such as the electron injection/ electron transporting (EI/ET) properties and charge transport balance, can also be conferred to the phosphorescent Ir III complexes to give excellent electroluminescent (EL) characteristics. Highly efficient red phosphorescent bis(5-(dimesitylboryl)-2-phenylpyridinato)iridium(acetylacetonate) (Ir-B-1) based on the above notion shows a very good compatibility with the choice of host materials which can furnish maximum current efficiency (h L ) of 22.2 cd A À1 , external quantum efficiency (h ext ) of 14.7% and power efficiency (h P ) of 21.4 lm W À1 for the devices constructed with the conventional host materials. So, these exciting results will not only provide both the systematic guidelines for the phosphorescent color variation on the Ir III complexes with B(Mes) 2 units as well as a deeper insight into the conventional color-tuning approach on ppy-type Ir III complexes, but also offer a simple outlet to afford unique electronic features to these phosphorescent emitters to show admirable EL performance.
A series of 2-vinylpyridine-type platinum(II) complexes bearing different main-group blocks (B(Mes)2, SiPh3, GePh3, NPh2, POPh2, OPh, SPh, and SO2Ph, where Mes = 2-morpholinoethanesulfonic acid) were successfully prepared. As indicated by the X-ray single-crystal diffraction, the concerned phosphorescent platinum(II) complexes exhibit distinct molecular packing patterns in the solid state to bring forth different interactions between individual molecules. The photophysical characterizations showed that the emission maxima together with phosphorescent quantum yield of these complexes can also be affected by introducing distinct main-group moieties with electron-donating or electron-withdrawing characters. Furthermore, these 2-vinylpyridine-type platinum(II) complexes exhibit markedly different photophysical and electrochemical properties compared with their 2-phenylpyridine-type analogues, such as higher-lying highest occupied molecular orbital levels and lower-energy phosphorescent emissions. Importantly, these complexes can show good potential as deep red phosphorescent emitters to bring attractive electroluminescent performances with Commission Internationale de L'Eclairage (CIE) coordinates very close to the standard red CIE coordinates of (0.67, 0.33) recommended by the National Television Standards Committee. Hence, these results successfully established structure-property relationship concerning photophysics, electrochemistry, and electroluminescence, which will not only provide important information about the optoelectronic features of these novel complexes but also give valuable clues for developing novel platinum(II) phosphorescent complexes.
Promoting triplet energy-transfer in novel phosphorescent polymers with platinum(II) polymetallayne backbones to achieve high EL performances with η L of 11.49 cd A -1 , η ext of 4.38% and η P of 3.78 lm W -1 .
Abstract:Two series of new phosphorescent copolymers with bicarbazole-based platinum(II) polymetallayne backbone have been successfully prepared through Sonogashira cross-coupling with different Ir III ppy-type (ppy=2-phenylpyridine anion) complexes as phosphorescent centers.The photophysical investigations not only indicate highly efficient triplet energy-transfer process from the polymetallayne segments to the phosphorescent units in the polymer solution, but also figure out the structure-property relationship between the triplet energy-transfer process and the energy-levels of different excited states. In addition, the phosphorescent copolymers can furnish yellow-emitting phosphorescent OLEDs (PHOLEDs) with high EL efficiencies with current efficiency ( L ) of 11.49 cd A -1 , external quantum efficiency ( ext ) of 4.38%, power efficiency ( P ) of 3.78 lm W -1 , and red-emitting PHOLEDs with L of 5.86 cd A -1 , ext of 10.1%, P of 2.29 lm W -1 , representing very decent electroluminescent performances ever achieved by the phosphorescent copolymers. This work herein not only furnishes very important clues for further polishing this category novel phosphorescent polymer, but also provides a new approach to design and synthesis of highly efficient phosphorescent copolymers. phosphorescent polymers. Playing the same role of the host materials in the phosphorescent OLEDs with small molecular triplet emitters, the organic segments in the phosphorescent polymers can act as the host of the phosphorescent blocks. Thus, the emission layer (EML) in PHOLEDs can be easily constructed by directly spin-coating a solution of the phosphorescent polymers, which can greatly simplify the device fabrication. Similar to their fluorescent counterparts, PHOLEDs also relates to the charge carrier injection/transporting in their EMLs.Thus, it seems that the phosphorescent polymers with conjugated backbones are preferred to promote the charge carrier injection/transporting in the EML of PHOLEDs. Another critical issue should be addressed in PHOLEDs based on conjugated phosphorescent polymers is blocking the undesired reverse energy-transfer from the emissive triplet states of the phosphorescent units to the non-emissive triplet states of the conjugated backbones in the phosphorescent polymers. 5 In order to achieve high EL performance in PHOLEDs, the reverse energy-transfer process should be restrained as far as possible. With the aim to fulfill this purpose, increasing the triplet energy level of the backbones of phosphorescent polymers should be a feasible way. Hence, the phosphorescent polymers with nonconjugated backbones have also been prepared. Clearly, this type polymer backbone seems unfavorable for charge carrier injection/transporting. In order to overcome the weakness associated with the nonconjugated backbones ...
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