Zuan Huang

Versatile phosphorescent color tuning of highly efficient borylated iridium(III) cyclometalates by manipulating the electron-accepting capacity of the dimesitylboron group

Several phosphorescent IrIII ppy-type complexes (ppy = 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 IrIII 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 IrIII 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 (ηL) of 22.2 cd A−1, external quantum efficiency (ηext) of 14.7% and power efficiency (ηP) of 21.4 lm W−1 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 IrIII complexes with B(Mes)2 units as well as a deeper insight into the conventional color-tuning approach on ppy-type IrIII complexes, but also offer a simple outlet to afford unique electronic features to these phosphorescent emitters to show admirable EL performance.

Dynamic dual stage phosphorescence chromatic change in a diborylated iridium phosphor for fluoride ion sensing with concentration discriminating capability

By adding a strongly electron-accepting B(Mes)2 group to the ppy-type ligand of phosphorescent iridium(III) cyclometalated complexes, more stabilized metal-to-ligand charge-transfer (MLCT) states can be obtained by transferring electron density from the pyridyl moiety to the boron atom of the B(Mes)2 group in the metallophosphors to give red phosphorescence. Taking advantage of the binding effect between boron atom and F− ion, the phosphorescent emission color of the iridium(III) cyclometalated complex can be dynamically changed by the external F− ions sequentially from red to yellow and to green through modulation of the charge-transfer emitting states, representing very unique F− ion sensing behavior. In the first step, destabilization of the MLCT states is caused by the weak binding between boron and F− ion, which is then accompanied by switching of the MLCT process to form high-energy MLCT states as induced by the strong binding between boron and F− ion in the second step. Not only does the dynamic phosphorescence chromatic variation depend significantly on the substitution mode of the B(Mes)2 moiety on the ppy ligands, but the dynamic emission response also would pave the way to the development of a novel F− ion sensor showing a unique concentration discrimination feature in aqueous solution with good color reversibility and optical response to the naked eye, high selectivity and sensitivity. All of these data provide valuable insight into the molecular design of a new generation of F− ion sensors featuring both concentration discriminating capability and good potential for practical applications.

Novel phosphorescent polymers containing both ambipolar segments and functionalized IrIII phosphorescent moieties: synthesis, photophysical, redox, and electrophosphorescence investigation

Two series of novel phosphorescent polymers have been successfully synthesized by the Suzuki cross-coupling reaction among functionalized phosphorescent IrIII ppy-type (ppy = 2-phenylpyridine anion) complex monomers with hole-injection/transporting (HI/HT) properties, fluorene-based silane moieties and triphenylamine-oxadiazole hybrid units showing ambipolar features. Their photo-physical, electrochemical, and electroluminescent (EL) properties have been investigated. The concerned results have indicated the efficient energy-transfer from the organic segments to the phosphorescent units in the polymer backbone. The electrochemical characterization has shown that introducing the triphenylamine-oxadiazole hybrid blocks can facilitate the injection processes for both kinds of charge carriers and afford ambipolar features to the copolymers. All these features associated with these novel phosphorescent polymers will guarantee their exceptional EL performances, which have been shown by organic light-emitting devices (OLEDs). The OLEDs based on these phosphorescent polymers can furnish a maximum current efficiency (ηL) of 30.54 cd A−1, an external quantum efficiency (ηext) of 12.93%, and a power efficiency (ηP) of 10.12 lm W−1. So, these attractive results will offer a new outlet to afford functionalized phosphorescent polymers for constructing highly efficient OLEDs with low-cost device fabrication.

Effective blocking of the molecular aggregation of novel truxene-based emitters with spirobifluorene and electron-donating moieties for furnishing highly efficient non-doped blue-emitting OLEDs

Several truxene-based blue fluorescent emitters bearing different functional moieties and peripheral spirobifluorene groups have been successfully designed and synthesized. Through tuning the chemical structures and electronic characters of the functional moieties, both optimized molecular configuration and elevated highest occupied molecular orbital (HOMO) energy levels have been afforded to the truxene-based emitters, representing a new effective strategy for solving the problems of molecular aggregation and poor charge carrier injection/transport associated with the truxene-based blue emitters. Owing to the sophisticated strategy, the concerned emitters can furnish highly efficient non-doped blue-emitting OLEDs with a maximum current efficiency (ηL) of 7.41 cd A−1, an external quantum efficiency (ηext) of 4.33%, and a power efficiency (ηP) of 6.79 lm W−1, representing the state-of-the-art EL efficiencies ever achieved by the truxene-based blue emitters. All promising results will not only show the great potential of the concerned truxene-based blue fluorescent emitters in the field of OLEDs, but also furnish valuable clues for developing high-performance truxene-based emitters.

Platinum(II) polymetallayne-based phosphorescent polymers with enhanced triplet energy-transfer: synthesis, photophysical, electrochemistry, and electrophosphorescent investigation

Two series of new phosphorescent copolymers with bicarbazole-based platinum(II) polymetallayne backbones have been successfully prepared through Sonogashira cross-coupling with different IrIII ppy-type (ppy = 2-phenylpyridine anion) complexes as phosphorescent centers. The photophysical investigations not only indicate a 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 produce yellow-emitting phosphorescent OLEDs (PHOLEDs) with high EL efficiencies and a current efficiency (ηL) of 11.49 cd A−1, an external quantum efficiency (ηext) of 4.38%, a power efficiency (ηP) of 3.78 lm W−1, and red-emitting PHOLEDs with a ηL of 5.86 cd A−1, ηext of 10.1%, and a ηP of 2.29 lm W−1, representing very decent electroluminescent performances achieved by the phosphorescent copolymers. Herein, this work not only furnishes very important clues for further polishing of this category novel phosphorescent polymer, but also provides a new approach to the design and synthesis of highly efficient phosphorescent copolymers.

Enhancing the electroluminescence performances of novel platinum(II) polymetallayne-based phosphorescent polymers through employing functionalized IrIII phosphorescent units and facilitating triplet energy transfer

Novel orange phosphorescent polymers with platinum(II) polymetallayne-based backbones have been successfully developed through Sonogashira cross-coupling among bicarbazole moieties, functionalized IrIII phosphorescent blocks with electron injection/transporting (EI/ET) features, and trans-[PtCl2(PBu3)2]. Importantly, the very efficient energy-transfer process is observed from the triplet states of the polymetallayne-based backbone to the triplet metal-to-ligand charge transfer states (3MLCT) of the phosphorescent units in the polymer backbone, which will guarantee the high phosphorescent ability of these polymers. Benefiting from the weak conjugation-extending ability of the platinum(II) ions, the polymetallayne-based backbones show high triplet energy-level to effectively block the undesired reverse energy-transfer process. Furthermore, the EI/ET features of the functionalized IrIII phosphorescent units should balance the hole injection/transporting (HI/HT) of the bicarbazole moieties to improve the EL performances of these phosphorescent polymers. Benefiting from these merits, the phosphorescent polymers can furnish solution-processed phosphorescent OLEDs (PHOLEDs) with high EL efficiencies with current efficiency (ηL) of 9.17 cd A−1, external quantum efficiency (ηext) of 4.50% and power efficiency (ηP) of 4.04 lm W−1, representing very decent electroluminescent performances achieved by the orange phosphorescent polymers. This work herein might not only show the great potential of platinum(II) polymetallayne as the host segments in phosphorescent polymers, but also provide a new outlet to design and synthesise highly efficient phosphorescent copolymers.

Synthesis of 2,2′-biimidazole-based platinum(II) polymetallaynes and tuning their fluorescent response behaviors to Cu2+ ions through optimizing the configuration of the organic spacers and steric effect

Under controlled conditions, platinum(II) polymetallaynes with different 2,2′-biimidazole-based organic spacers have been synthesized readily. Their photophysical properties and fluorescent response behaviors to Cu2+ ions have been investigated in detail. By adjusting both the configuration of the 2,2′-biimidazole-based spacers and the steric effect, the fluorescent response behaviors of the polymetallaynes to Cu2+ ions can be tuned dramatically. The fluorescent signal from the polymetallayne with an optimized structure can be quenched rapidly by Cu2+ ions with a high Stern–Volmer constant KSV of ca. 6.8 × 104 M−1 and a low detecting limit (DL) of ca. 0.99 ppm. These results not only highlight the great potential of these polymetallaynes as novel Cu2+ sensors, but also provide new strategies for optimizing the sensing abilities of the 2,2′-biimidazole-based ion sensors.

CCDC 942860: Experimental Crystal Structure Determination

Related Article: Xiaolong Yang, Xianbin Xu, Jiang Zhao, Jing-shuang Dang, Zuan Huang, Xiaogang Yan, Guijiang Zhou, Dongdong Wang|2014|Inorg.Chem.|53|12986|doi:10.1021/ic502122t