Versatile Benzimidazole/Triphenylamine Hybrids: Efficient Nondoped Deep‐Blue Electroluminescence and Good Host Materials for Phosphorescent Emitters

Abstract

Two new bipolar compounds, N,N,N',N'-tetraphenyl-5'-(1-phenyl-1H-benzimidazol-2-yl)-1,1':3',1''-terphenyl-4,4''-diamine (1) and N,N,N',N'-tetraphenyl-5'-(1-phenyl-1H-benzimidazol-2-yl)-1,1':3',1''-terphenyl-3,3''-diamine (2), were synthesized and characterized, and their thermal, photophysical, and electrochemical properties were investigated. Compounds 1 and 2 possess good thermal stability with high glass-transition temperatures of 109-129 degrees C and thermal decomposition temperatures of 501-531 degrees C. The fluorescence quantum yield of 1 (0.52) is higher than that of 2 (0.16), which could be attributed to greater pi conjugation between the donor and acceptor moieties. A nondoped deep-blue fluorescent organic light-emitting diode (OLED) using 1 as the blue emitter displays high performance, with a maximum current efficiency of 2.2 cd A(-1) and a maximum external efficiency of 2.9 % at the CIE coordinates of (0.17, 0.07) that are very close to the National Television System Committee's blue standard (0.15, 0.07). Electrophosphorescent devices using the two compounds as host materials for green and red phosphor emitters show high efficiencies. The best performance of a green phosphorescent device was achieved using 2 as the host, with a maximum current efficiency of 64.3 cd A(-1) and a maximum power efficiency of 68.3 lm W(-1); whereas the best performance of a red phosphorescent device was achieved using 1 as the host, with a maximum current efficiency of 11.5 cd A(-1), and a maximum power efficiency of 9.8 lm W(-1). The relationship between the molecular structures and optoelectronic properties are discussed.

Functionalization of phosphorescent emitters and their host materials by main-group elements for phosphorescent organic light-emitting devices

“…Other bipolar hosts TPAPBA1 and TPAPBA2 have also been obtained by employing phenylbenzimidazole. 161 Due to their stronger conjugation, they show low E T which makes them suitable hosts for green phosphorescent emitters. Owing to its more twisted configuration, TPAPBA1 shows a higher E T of 2.55 eV than that of TPAPBA2 (2.41 eV) (Table 6).…”

A Bipolar Transporter as an Efficient Green Fluorescent Emitter and Host for Red Phosphors in Multi‐ and Single‐Layer Organic Light‐Emitting Diodes

“…A simple and viable strategy for designing them is to simultaneously incorporate an electron donor (D) and an electron acceptor (A) into one molecular skeleton as the basis of a bipolar characteristic. [5][6][7][8][9][10] The advantage of this strategy also rests on the flexibility in optimizing the electronic and optical properties of these bipolar materials through smart selection and chemical tailoring of the D-A pairs. Theoretically, given a perfect balance of carrier injection and transport inside the anode/organic/cathode system, high-efficiency single-layer OLEDs could be readily realized, which indeed are commercially much more favorable than complicated multilayer devices.…”

T‐Shaped Benzimidazole Derivatives as Blue‐Emitting Materials: The Role of C2 Substituents on Photophysical Properties

“…A broad asymmetric band, probably comprising at least two electronic transitions, dominates the absorption spectrum. The absorption peaks at approximately 279–307 nm are assigned to the localized π–π* transitions of the chromophores that include fluorene, pyrene, carbazole and triphenylamine . The longer wavelength peak at approximately 350 nm is attributed to either the delocalized π–π* transition or ICT from the triphenylamine donor to the benzimidazole acceptor .…”