A new class of neutral bis-tridentate Ir(III) metal complexes that show nearly unitary red, green, and blue emissions in solution is prepared and employed for the fabrication of both monochrome and white-emitting organic light-emitting diodes, among which a green device gives external quantum efficiency exceeding 31%.

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...

A series of new bis-tridentate Ir(iii) complexes (1/1b, 2/2b and 3/3b) incorporating both bis(imidazolylidene)benzene and dianionic functional pyrazolyl (or phenyl) pyridine chelates have been synthesized, among which complexes 2 and 2b exhibit intense and structural sky-blue emission in both solution and solid states. In stark contrast, 1/1b is non-emissive in solution, while 3/3b reveals highly red-shifted emission with a featureless spectral profile. This variation in photophysics is associated with the interchange of metal-chelate bonding in the selected tridentate chelate, which affects both the crystal field stabilization energy and the ππ* transition character of the resulting Ir(iii) metal complexes. In 1/1b, the stabilized metal-centered (MC) dd excited states induce a dominant radiationless channel that accounts for the lack of emission in solution. The appreciable ligand-to-ligand charge transfer (LLCT) in 3/3b rationalizes its broad and featureless emission, which is different from the dominant intraligand ππ* transition in 2/2b. The combination of experimental and theoretical approaches thus provides fundamental insight into the influence of chelates as well as the metal-chelate interaction, which is beneficial for the future design of efficient and robust Ir(iii) phosphors for OLED applications.