The Unusual Electrochemical and Photophysical Behavior of 2,2‘-Bis(1,3,4-oxadiazol-2-yl)biphenyls, Effective Electron Transport Hosts for Phosphorescent Organic Light Emitting Diodes

Abstract

The fluorescence and phosphorescence of 2,2'-bis(5-phenyl-1,3,4-oxadiazol-2-yl)biphenyl shows good spectral matching with the absorption spectra of the MLCT1 and MLCT3 transitions of Ir(ppy)3. The red-shift of the 0-0 band in the phosphorescence at 77 K is due to the intramolecular pi-pi interactions between the oxadiazole side chains. Maximum brightness of 43,000 cd/m2 with an efficiency of 26 cd/A at 200 cd/m2 was achieved when BOBP was used as the host material for Ir(ppy)3 in the PHOLED study. [structure: see text].

Effective adjustment of the optoelectronic properties of organic conjugated materials by synthesizing p-n diblock molecules

“…They synthesized a novel p-n diblock copolymer 13, which is composed of an electron-rich moiety carbazole (CBZ) and an electron-deficient aromatic OXD to balance the injection and transport of holes and electrons ( Figure 5) [14]. Electrochemical analyses by cyclic voltammetry (CV) indicate that the polymer can be reversibly n-doped and irreversibly p-doped.…”

Molecular hosts for triplet emitters in organic light-emitting diodes and the corresponding working principle

“…Taking Ir(ppy) 3 (3), the most intensively studied phosphorescent material in PhOLEDs, as an example, the variations of performance are demonstrated in Table 1, the features of host materials and different devices characteristics, together with device performance are compared, and the related references are listed for further survey [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44].…”

“…Toward searching hosts for triplet emitters, as shown in Figure 10, typical electron transport materials with functionalities of triazole (TAZ1 (26) [34,79]), phenathroline (BCP (27) [34]), oxadiazole (BOBP-3 (28) [35,38]), and silole (si(bph) 2 (29) [80]) were studied. Mainly due to their relatively low triplet energy, these electron transport materials are scarcely used for the blue triplet emitter.…”

“…Later, they reported that with TAZ1 (26) and (ppy) 2 Ir(acac) (4), the green device with the efficiency of 19.0% (65 lm/W) was obtained [79]. Oxadiazole derivatives (BOBP-3 (28)) as triplet hosts were introduced by Lee and Leung et al [35,38]. BOBP-3 (28) and Ir(ppy) 3 (3) based device exhibits an efficiency of 24 cd/A (10 lm/W).…”

“…BOBP-3 (28) and Ir(ppy) 3 (3) based device exhibits an efficiency of 24 cd/A (10 lm/W). This device was claimed of longer lifetime compared to the corresponding CBP (7) host based device [38]. Lee et al regarded that EML consisting of BOBP-3 (28) (they termed as OXD) doped with Ir(ppy) 3 (3) was an ambipolar layer, due to the electron transport property of BOBP-3 (28) and the hole transport property of Ir(ppy) 3 (3) [35].…”