Triarylboryl‐Functionalized Oxadiazole as a Host Material with Electron Transporting Property for Green PhOLEDs

Abstract

A triarylboryl-functionalized oxadiazole compound, 2,5-bis-(m-dimesitylboryl-phenyl)-1,3,4-oxadiazole (1) was prepared and characterized to investigate multi-functional properties in phosphorescent OLEDs (PhOLEDs). X-ray crystal structure revealed that two Mes 2 B groups are oriented toward the same side and the entire fragments of oxadiazole, phenylene, and trigonal boron are in a nearly coplanar arrangement. From the optical and electrochemical measurements, 1 was shown to possess high triplet energy (E T = 2.75 eV) and deep HOMO (E HOMO = 6.02 eV) and low LUMO levels (E LUMO = 2.53 eV), which are suitable for electron transporting (ETM) and/or host materials in PhOLEDs. Green PhOLED devices incorporating 1 as electron transporting material (ETM), host, or host/ETM were fabricated and compared their performance with that of the devices based on the well-known CBP (9,9 0 -(1,1 0 -biphenyl)-4,4 0 -diylbis-9H-carbazole) host and TPBi (1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene) ETM. Among them, the devices based on 1 as host/ETM showed the highest performance that is comparable to that of the reference device.

Ultrafast Intermolecular Energy Transfer in OLED Materials: Excited-State Dynamics of a Blend of Poly(vinylcarbazole) and Oxadiazole Derivative in Solution and Film States

“…A significant investigation has been carried out to increase the performance of the small molecules or polymers used in thin-film OLEDs because of their potential usages in large-scale, cheap, environmentally friendly, energy-saving, flat panel displays and solid-state lighting technologies. − The most widely used materials in the UV-OLEDs are nonconjugated polyvinyl carbazole (PVK ), an electron-rich and hole-transporting polymer, , and oxadiazole, electron-transport materials. , The inherent photophysical characteristics of PVK and OXD , including the formation of excimers, exciplex, electroplex, and feasible energy transfer, were explored to improve the efficiency of the OLED devices. − The electroluminescence of the blend of PVK and OXD exhibited the exciplex emission with a current efficiency of 1.63 Cd/A . Using iridium complex as the guest, green electrophosphorescent light-emitting diodes and light-emitting electrochemical cells were made with a mixture of PVK and oxadiazole derivatives as the host, where the excitation energy was extracted by the Förster resonance energy transfer (FRET) and charge trapping mechanism, leading to higher external quantum efficiency.…”

“…1−4 The most widely used materials in the UV-OLEDs are nonconjugated polyvinyl carbazole (PVK), an electron-rich and hole-transporting polymer, 5,6 and oxadiazole, electron-transport materials. 7,8 The inherent photophysical characteristics of PVK and OXD, including the formation of excimers, exciplex, electroplex, and feasible energy transfer, were explored to improve the efficiency of the OLED devices. 9−11 The electroluminescence of the blend of PVK and OXD exhibited the exciplex emission with a current efficiency of 1.63 Cd/A.…”

Blue Phosphorescent Organic Light‐emitting Diode Using a Novel Starburst‐type Donor and Acceptor Material as a Co‐host

“…Phosphorescent materials have been used for the efficient harvesting of triplet excitons in organic light‐emitting diode (OLED) devices . In the case of red and green phosphorescent devices, phosphorescent dopants and host materials having excellent efficiencies and device lifetime characteristics have been developed and used in commercialized devices . However, in the case of blue phosphorescent devices, although theoretical levels with maximum external quantum efficiencies of ~30% have been reached, drawbacks remain for these devices, including the short lifetimes, high power consumption, and poor color purity because of the molecular structures of the phosphorescent hosts and dopant material, and operating environments requiring high electric fields …”