Bis‐Tridentate Ir(III) Metal Phosphors for Efficient Deep‐Blue Organic Light‐Emitting Diodes

Abstract

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...

High‐Efficiency Deep‐Blue‐Emitting Organic Light‐Emitting Diodes Based on Iridium(III) Carbene Complexes

“…The second is that as the energy of the emissive triplet state increases, nonradiative recombination via thermally accessible metal‐centered excited states becomes increasingly problematic, leading to emitter degradation . Finally, most iridium(III) complexes do not meet the deep blue chromaticity requirements, and instead possess CIE y ordinates greater than 0.1 as their triplet energies are not sufficiently high (at least 2.8 eV);[3b,8] those that do possess maximal external quantum efficiency (EQE max ) values < 10% …”

Solution electrowriting of highly stable TiN nanofiber pattern for transparent electrode under extreme environment

“…Transparent electrodes, a crucial building block in optical‐electronic devices such as liquid crystal displays (LCD), organic light‐emitting diodes (OLED), solar cells and touch screens, have recently attracted increasing attention . Driven by their broad application fields, more and more efforts have been endeavored on developing new transparent electrodes with high performance in the past few decades.…”

Smart Design on the Cyclometalated Ligands of Iridium(III) Complexes for Facile Tuning of Phosphorescence Color Spanning from Deep‐Blue to Near‐Infrared

“…First, to confine the recombination of hole/electron and triplet excitons inside the deep‐blue EML, bis[2‐(diphenylphosphino)phenyl] ether oxide (DPEPO) was employed as the host material. DPEPO has a large E T of 3.35 eV, which is sufficient for Ir1 ( E T = 3.12 eV) to harvest the triplet energy from the host efficiently. The frontier energy levels of Ir1 are within that of DPEPO, resulting in a good energy transfer from host to dopant.…”

“…In the past two decades, great attention has been focused on designing Ir(III) luminophores that exhibit visible phosphorescent emissions spanning from blue to red . However, literature reports about near‐infrared (NIR) Ir(III) emitters are still rare, despite their great application importance on information‐secured devices, communications, biosensors and phototherapy .…”