Synthesis and optoelectronic properties of a monodispersed macrocycle oligomer consisting of three triarylamine units

A monodispersed macrocyclic oligomer constructed by three triarylmine units ((TPAT)3) was designed and readily synthesized from the monomer of 3-(4′-(phenyl(4″-methylphenyl)amino)-phenyl)pentan-3-ol (TPAT) by means of a simple Friedel–Crafts alkylation reaction. The structure of the resultant macrocycle was examined using FT-IR, NMR and MALDI-TOF mass spectroscopy. Compared with 1,10-bis(di-4-tolylaminophenyl) cyclohexane (TAPC) and tri-p-tolylamine (TTA), (TPAT)3 possesses the three-dimensional chair conformation and the higher Tg. In the photoluminescence (PL) spectrum of (TPAT)3 film, there are no excimer emission peaks in the range of 400–550 nm region as those of TAPC and TTA. Besides an EL peak at 386 nm, the single-layer device occured only the 438 nm excimer emission peak, whose intensity increased with the excitation voltage increase. Using 1,3,5-Tris(N-phenylbenzimidazol-2-yl)-benzene (TPBI) as the electron-transporting layer, the resulting double-layer device ITO/(TPAT)3 (40 nm)/TPBI (40 nm)/Mg:Ag (10:1; 50 nm)/Ag (100 nm) only exhibited a 438 nm maximum symmetrical emission peak under an excitation voltage of 14 V. However, as the applied voltage was increased from 14 V to 19 V, the intensity of the symmetrical curve with a 468 nm peak from exciplex emission gets stronger and stronger. In fact, the resultant emission curve was asymmetrical, due to the overlap of two symmetrical curves with 438 nm and 468 nm peaks, respectively. The maximum luminance and luminous efficiency are 2240 cd m−2 at 18.8 V and 1.73 cd A−1 at 1878 cd m−2 (13.9 V).