which the developments still lag behind the green and red counterparts due to the intrinsically wider energy gaps. [2] Efficient blue-emitters are expected to reduce power consumption and improve color gamut; therefore, they have emerged as one paradigm of the full-color OLED displays and solid-state lighting. [3] Among the various known blue phosphors, the sky-blue emitter FIrpic is considered to be the archetypal design; hence, its modulation is at the forefront of modern research in OLEDs. [4] OLEDs made with FIrpic typically have Commission Internationale de l'Eclairage (CIE (x,y) ) coordinates of (0.17, 0.34) which is far from the National Television Standards Committee pure blue values of (0.14, 0.08). Progress with blue phosphors is further complicated by other issues, such as chemical and physical stabilities, emission quantum yield, and relative radiative lifetime. Moreover, almost all reports of decent blue phosphors were focused on the so-called tris-bidentate architectures, i.e., with either three bidentate cyclometalates of higher ligand-centered ππ* energy gap or two of these cyclometalate plus a third bidentate ancillary. [5] However, these complexes suffer from possible chelate dissociation upon excitation, giving inferior device performances and longevity. [6] Recently, Whittle and Williams, [7] Haga and co-workers, [8] De Cola and co-workers, [9] and Esteruelas and co-workers [10] have independently conducted studies on emitters bearing two tridentate chelates; namely bis-tridentate metal complexes. This class of molecular designs is expected to be more robust and should be of higher efficiency attributed to the concomitant higher rigidity versus the traditional design bearing three bidentate chelates. [11] Despite the obvious advantages, these associated studies were greatly hampered by the lack of systematic syntheses and poor performances on OLEDs. These difficulties were recently solved by proper selection of chelates to give the charge-neutral architecture [12] and the installment of a higher field strength coordination unit. [13] One known bis-tridentate metal complex is the sky-blue Ir(III) phosphor [Ir(mimf)(pzpyph F )] (SB = "sky-blue"), [14] where the tridentate 6-pyrazolyl-2-phenylpyridine (pzpyph F ) and pincer dicarbene chelate (mimf) act as the chromophoric and ancillary chelates, respectively (Scheme 1). These ligands control the emission color and give the greater ligand field strength needed for the efficient phosphors. [15] Hence, the OLED derived from SB gave maximum external quantum efficiency (max. EQE) of 27% and EQE of 24% at the practical Emissive Ir(III) metal complexes possessing two tridentate chelates (bis-tridentate) are known to be more robust compared to those with three bidentate chelates (tris-bidentate). Here, the deep-blue-emitting, bis-tridentate Ir(III) metal phosphors bearing both the dicarbene pincer ancillary such as 2,6-diimidazolylidene benzene and the 6-pyrazolyl-2-phenoxylpyridine chromophoric chelate are synthesized. A deep-blue organic light-em...

Sky‐blue and blue‐emitting, carbazolyl functionalized, bis‐tridentate Ir(III) phosphors Cz‐1–Cz‐3 with bright emission and short radiative lifetime are successfully synthesized in a one‐pot manner. They exhibit very high photostability against UV–vis irradiation in degassed toluene, versus both green and true‐blue‐emitting reference compounds, i.e., fac‐[Ir(ppy)3] and mer‐[Ir(pmp)3]. Organic light‐emitting diodes (OLEDs) based on Cz‐2 exhibit maximum external quantum efficiency (EQE) of 21.6%, EQE of 15.1% at 100 cd m−2, and with CIEx , y coordinates of (0.17, 0.25). This study provides a conceptual solution to the exceedingly stable and efficient blue phosphor. It is promising that long lifespan blue OLED based on these emitters can be attained with further engineering of devices suitable for commercial application.

There is growing interest in the bis-tridentate Ir(III) emitters as they are expected to display both improved emission efficiency and improved photostability. Herein, we turned to the new emitters m2h-1−3 and m6h-1−3, bearing a pincer carbene ancillary and a chromophoric chelate derived from judiciously selected phenyl-pyrimidine-pyrazole entities (pzm2h F )H 2 and (pzm6h F )H 2 , which differ in terms of the location of phenyl and pyrazole substituents on the central pyrimidine. Density functional theory calculations revealed a notable change in the spin density distribution from the pyrimidine-pyrazolate entity in m2h to the pyrimidine-phenyl fragment in m6h. As a consequence, the m6h emitters exhibited both shortened emission lifetimes and improved stabilities during extensive photolysis in solution, while corresponding organic light-emitting diodes (OLEDs) doped with green-emitting m6h-1 and sky-blue-emitting m6h-2 and m6h-3 exhibited external quantum efficiencies of 17.6, 15.9, and 17.6%, respectively, superior to those of all of their m2h counterparts at a practical luminance of 10 3 cd/m 2 . This finding suggests a new methodology for fine-tuning the electronic transition that is important to high-performance and durable phosphorescent OLEDs. 49 increase of the emitting excited state energy, which is needed 50 to achieve blue emission, also reduces the energy separation 51 between this emitting excited state and the upper-lying metal-52 centered (MC) dd states. These quenching states are capable 53 of fostering a fast nonradiative decay, giving an unsatisfactory 54 efficiency. 19−21 Notably, one method for blocking this 55 nonradiative process is to employ metal phosphors with a 56 bis-tridentate architecture, 22−24 for which the imposed higher 57 rigidity and multiple metal−chelate coordination bonding are 58 expected to offer higher ligand-field strength and, hence, a 59 much destabilized MC dd excited state and more efficient blue 60 emission.

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