Efficient Blue‐ and White‐Emitting Electrophosphorescent Devices Based on Platinum(II) [1,3‐Difluoro‐4,6‐di(2‐pyridinyl)benzene] Chloride

Abstract

Electrophosphorescence based on cyclometalated Ir and Pt complexes has attracted broad attentions from academia and industries, owing to the potential of these complexes for harvesting both electrogenerated singlet and triplet excitons to achieve 100% internal quantum efficiency.[1] Efficient blue, green, and red phosphorescent organic light-emitting devices (OLEDs) have been fabricated with the judicious ligand design of these Ir and Pt complexes. [2][3][4] Compared with reported efficient green-and red-phosphorescent OLEDs, [2] few choices of materials are provided for the fabrication of blue-phosphorescent OLEDs, which is considered to be important to the applications of OLEDs for displays and solid-state lighting. So far, the approaches to achieve efficient blue-phosphorescent OLEDs are focused on Ir-based complexes, by either adopting high-tripletenergy ligands such as 4,6-difluorophenylpyridine [3a-e] and 1-phenyl-3-methylimidazolium [3f] or by using electronwithdrawing ancillary ligands such as picolinate (FIrPic), [3a] tetrakis(1-pyrazolyl)borate (FIr6), [3b,c] triazolate (FIrtaz), and tetrazolate (FIrN4).[3d] Although some Pt complexes have been reported to show blue phosphorescent emission at room temperature, the quality of light emission and the efficiency of devices that use current Pt complexes are not comparable to those using Ir alternatives.[4a-c] For example, devices based on (Fig. 1) Therefore, designing and studying Pt(N^C^N)X materials for application in blue-and white-phosphorescent OLEDs is a worthwhile undertaking. In this Communication we report the photophysics, electrochemistry, and electroluminescent properties of a novel platinum [1,3-difluoro-4,6-di(2-pyridinyl)benzene] chloride , shown in Figure 1. Blueemitting devices based on this complex showed a peak EQE of 16% ph/el and CIE coordinates of (0.15, 0.26). Single-dopant white-emitting devices based on this complex showed a peak EQE of ca. 9.3% ph/el and CIE coordinates of (0.33, 0.36). The electrochemistry of FPt and Pt-4 was examined using cyclic voltammetry. Pt-4 showed a reversible reduction at À2.06 V (versus Fc þ /Fc) and an irreversible oxidation at 0.5 V in N,N-dimethyl formamide (DMF) solution, whereas FPt has a reversible reduction at À2.29 V and an irreversible oxidation at 0.5 V, comparable to the literature data.[4a]The lower reduction potential of Pt-4 suggests that Pt-4 has a deeper lowest unoccupied molecular orbital (LUMO) energy level than FPt. The room-temperature absorption and emission spectra of FPt and Pt-4 are shown in Figure 2. Both of them display very intense absorption bands (e > 1.5 Â 10 4 M À1 cm À1 ) at wavelength between 250-300 nm, assigned to 1 p-p* transitions of the cyclometalating ligands.Weaker bands at longer wavelength (300-400 nm, e ¼ 5000-9000 M À1 cm À1) were assigned to metal-to-ligand charge-transfer (MLCT) transitions. The lowest-energy absorption bands (460-470 nm, e ¼ 40-150 M À1 cm À1

Epindolidiones—Versatile and Stable Hydrogen‐Bonded Pigments for Organic Field‐Effect Transistors and Light‐Emitting Diodes

“…Excimer-emitting materials are nevertheless an interesting concept to achieve polychromic emission from a single semiconducting material, and have been suggested as a possible route to achieving practical white-light emitting OLEDs. [36][37][38] …”

A Synthesis and Characterization of Pt(II) Complexes with Bipyrimidin-based Back-bone System

“…발광 착체들의 중심금속으로는 이리듐(III)이 많이 사용되고 있지만, 백금(II)착체에 대한 관심도 증가하고 있다 [11]. 백금의 경우, 단파장(400~500 nm)에서의 발광특성이 보고되어 있고 결합된 배위 자의 종류에 따라서 발광파장이 이동되는 것이 보고되었다 [13][14][15][16].…”

Efficient organic light-emitting devices with platinum-complex emissive layer

“…16 Emissive layers were sandwiched between a 20 nm hole-transporting/electron-blocking 1,3-bis͑N-carbazolyl͒benzene ͑mCP͒ layer and 40 nm electron-transporting/hole-blocking 1,3-bis͓4-tert-butylphenyl-1,3,4-oxadiazolyl͔phenylene ͑OXD-7͒ layer. Poly͓3,4-ethylenedioxythiophene͔ doped with poly͓styrene-sulfonate͔ ͑PEDOT:PSS͒ and NPB functioned as the holeinjection and hole-transporting layers, respectively.…”

“…Values of the highest occupied molecular orbital ͑HOMO͒ and lowest unoccupied molecular orbital ͑LUMO͒ levels of organic materials, work function of the electrodes are cited based on published literature. 15,16,18 A noticeable mismatch between the LUMO level of mCP and HOMO level of OXD-7 and those of the platinum-complexes allows for the confinement of carrier re- combination activity in the platinum-complex layer. In addition, the high triplet state energy of mCP and OXD layers minimizes possible quenching of excited states formed in the emissive layer.…”

“…8% and 15 lm W −1 , respectively. In order to improve the efficiency, platinum͑II͓͒1,3-difluoro-4,6-di͑2-pyridinyl͒benzene͔ chloride ͑Pt-4͒, 16 an efficient blue phosphor, is incorporated in the device structure. Figure 3͑c͒ displays the EL spectra of devices with an emissive layer structure of Pt-4 ͑0.1 nm, 0.2 nm͒/FPt ͑0.7 nm͒ at different drive voltages.…”