Synthesis, characterization, and hole-transporting properties of pyrenyl N-substituted triazatruxenes

Abstract

Two new pyrenyl triazatruxene derivatives (TAT1 and TAT2) were successfully synthesized via Br₂-catalyzed cyclotrimerization of indole and Suzuki cross-coupling with pyrene-1-boronic acid. These compounds exhibited maximum absorption around 344–351 nm and maximum emission around 472–483 nm in CHCl₃ solution. The electrochemical investigation by cyclic voltammetry (CV) suggested that the HOMO and LUMO energy levels of these compounds were around −5.3 and −2.4 eV, respectively. The performance of TAT2 as a hole-transporting material was three-times better than that of the commercial compound N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD). The electroluminescent device of the structure ITO/PEDOT:PSS/TAT2/Alq₃/LiF:Al exhibits a bright green emission with a maximum luminance of 31 971 cd m⁻² at 10.8 V and a turn-on voltage of 2.6 V. In addition, the use of spin-casted films of TAT1 or TAT2 doped with 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) as greenish blue-emitting materials are demonstrated.