Pyrenyl truxenes as materials in organic light-emitting diodes

Abstract

A new series of truxene derivatives with different numbers of dipyrenylcarbazole substituents have been synthesized via C-N cross-coupling. The Cu-catalyzed C-N coupling between the iodinated truxene core and dipyrenylcarbazole thus provides the target molecules (1-3) which are characterized by 1H-NMR, 13C-NMR and MALDI-TOF mass spectroscopy. These compounds emitted in the blue region (lem= 421 to 423 nm) and showed excellent thermal stabilities (Td10% above 440°C) suitable for application in optoelectronic devices. All compounds were used as hole-transporting non-doped emitters and BCP as a hole blocking layer in the OLEDs with the structure of ITO/PEDOT:PSS/1–3/BCP/LiF:Al. All devices emitted deep blue color according to the CIE coordinates (CIE, x= 0.15, y= 0.10 to 0.19) with high luminance efficiencies as compared to the reference device using NPB. Among the three materials, compound 2 could give lead to the best device performance with high maximum brightness of 8,001 cd/m2 at 9.6 V and turn-on voltage (Von) at 3.4 V. In addition, the hole-transport properties of these compounds compared with the commercial standard NPB were investigated using devices configuration of ITO/PEDOT:PSS/1–3/Alq3/LiF:Al. All devices displayed a bright green emission of Alq3 (lem= 512 to 517 nm, CIE 0.26, 0.50). Their ability as HTL for green OLEDs was comparable to a common hole-transporter NPB. The device based on 2 exhibited the best performance with highest maximum brightness of 44,773 cd/m2 at 10.8 V and turn-on voltage (Von) at 2.8 V.