Design of star-shaped molecular architectures based on carbazole and phosphine oxide moieties: towards amorphous bipolar hosts with high triplet energy for efficient blue electrophosphorescent devices

Abstract

With a carbazole moiety as the electron donor and a phosphine-oxide moiety as the electron acceptor, two novel star-shaped bipolar hosts, 4,4 0 ,4 00 -tri(N-carbazolyl)triphenylphosphine oxide (TCTP) and 3,6bis(diphenylphosphoryl)-9-(4 0 -(diphenylphosphoryl)phenyl)carbazole (TPCz), have been designed and synthesized. Their topology structure differences are that the phosphine-oxide moiety is located in the molecular centre and the periphery for TCTP and TPCz, respectively. The star-shaped architecture imparts them with high decomposition temperatures (T d : 497 C for TCTP and 506 C for TPCz) and results in the formation of a stable amorphous glassy state (T g : 163 C for TCTP and 143 C for TPCz), while the phosphine oxide linkage ensures the disrupted conjugation and the high triplet energy (>3.0 eV). In addition, both TCTP and TPCz possess a bipolar transporting capability. However, TCTP mostly transports holes and TPCz primarily conducts electrons. On the basis of appropriate device configurations, high performance blue electrophosphorescent devices with comparable efficiency (35.0-36.4 cd A À1 , 15.9-16.7%) have been realized using TCTP and TPCz as the host for the blue phosphor, respectively. Compared with the unipolar host, 4,4 0 ,4 00 -tri(N-carbazolyl)triphenylamine (TCTA, 15.9 cd A À1 , 7.8%), the efficiency is improved by more than two-fold. As far as the obtained state-of-the-art performance is concerned, we think that these novel materials should provide an avenue for the design of amorphous bipolar hosts with high triplet energy used for blue PhOLEDs on a star-shaped scaffold.

Diffusion – the Hidden Menace in Organic Optoelectronic Devices

“…Under thermal stress the NR profile began to change at 90 °C, which is above the reported bulk glass transition temperatures of CBP [25][26][27] and BCP, [28][29][30] but below that of TCTA. [31,32] Modeling showed that the change was consistent with the d-BCP layer beginning to diffuse into the emissive guest:host layer ( Figure 2). After stressing the film at 100 °C the d-BCP was found to have diffused throughout the Ir(ppy) 3 :CBP layer but not into the d-TCTA.…”

Properties modulation of organic semi-conductors based on a donor-spiro-acceptor (D-spiro-A) molecular design: new host materials for efficient sky-blue PhOLEDs

“…31 Using an insulating heteroatom is also an efficient strategy to obtain high E T materials with short π-conjugated pathway. 39 HOMO/LUMO levels respectively lie at -5.25 eV/-1.67 eV, and the disrupted conjugation via phosphine-oxide linkage preserves a high E T of 3.03 eV. Thus, the electronic structure of the bipolar molecules is almost identical to those of the corresponding central core, which is a crucial point to avoid the decrease of E T .…”

A Novel, Bipolar Polymeric Host for Highly Efficient Blue Electrophosphorescence: a Non‐Conjugated Poly(aryl ether) Containing Triphenylphosphine Oxide Units in the Electron‐Transporting Main Chain and Carbazole Units in Hole‐Transporting Side Chains

“…Here, TPCz stands for 3,6-bis(diphenylphosphoryl)-9-(4-(diphenylphosphoryl)phenyl)-9H-carbazole, which acts as a hole/exciton-blocking material, and was developed by our group. [ 32 ] The concentration of FIrpic varied from 2.5 wt% to 15 wt%; the best device performance was obtained with a dopant concentration of 5 wt% ( Figure 5 ). This device showed a turn-on voltage of 6 V, a maximum luminous effi ciency ( η l,max ) of 23. , the EQE still remained as high as 9.1%.…”