Indolo[3,2-b]carbazole/benzimidazole hybrid bipolar host materials for highly efficient red, yellow, and green phosphorescent organic light emitting diodes

Abstract

By incorporating electron-accepting benzimidazole and electron-donating indolo [3,2-b]carbazole into one molecule, two novel donor-acceptor bipolar host materials, TICCBI and TICNBI, have been synthesized. The photophysical and electrochemical properties of the hybrids can be tuned through the different linkages (C-or N-connectivity) between the electronic donor and acceptor components. The promising physical properties of these two new compounds made them suitable for use as hosts doped with various Ir or Os-based phosphors for realizing highly efficient phosphorescent organic light emitting diodes (PhOLEDs). PhOLEDs using TICCBI and TICNBI as hosts incorporated with Irbased emitters such as green (PPy) 2 Ir(acac), yellow (Bt) 2 Ir(acac), and two new red emitters (35dmPh-6Fiq) 2 Ir(acac) (i3) and (4tBuPh-6Fiq) 2 Ir(acac) (i6) accomplished high external quantum efficiencies ranging from 14 to 16.2%. Nevertheless, the red PhOLED device incorporating TICNBI doped with the red emitter osmium(II) bis[3-(trifluoromethyl)-5-(4-tert-butylpyridyl)-1,2,4-triazolate] dimethylphenylphosphine [Os(bpftz) 2 (PPhMe 2 ) 2 ] achieved a maximum external quantum efficiency, current efficiency, and power efficiency of 22%, 28 cd A À1 , and 22.1 lm W À1 , respectively, with CIE coordinates of (0.65,0.35). The external quantum efficiency remained high (20%) as the brightness reached to 1000 cd m À2 , suggesting balanced charge fluxes within the emitting layer, rendering devices with limited efficiency roll-off.

Pyrrolo[1, 2‐a]quinoxaline‐Based Bipolar Host Materials for Efficient Red Phosphorescent OLEDs

“…Also this can be explained by their different geometrical characteristics, molecular planarity which indicategood intramolecular charge transfer between carbazole donor and pyrrolo[1, 2‐a]quinoxaline acceptor. The more coplanar conformation of 4CBZ‐PQ is expected to generate more ordered molecular arrangement, which is favorable to rapid charge hopping and transportation and higher current densities in devices …”

Molecular Topology Tuning of Bipolar Host Materials Composed of Fluorene‐Bridged Benzimidazole and Carbazole for Highly Efficient Electrophosphorescence

“…The results from single-carrier devices indicate that the electron-transport behavior is better and the hole-transport property is worse on altering the linking topology from C to N connectivity of the benzimidazole unit, which is consistent with our previous report of indolocarbazole-benzimidazole hybridized materials (TICCBI and TICNBI). [15] To evaluate the utilization of CzFCBI and CzFNBI as host materials for different dopants (from blue to red), we selected blue [bis (4,6-difluorophenyl) [16] green bis (2phenylpyridinato) [17] yellow-green bis(meta-tolylpyrimidine)iridium- [5b] and red bis[3-(trifluoromethyl)-5-(4-tertbutylpyridyl)-1,2,4-triazolate]dimethylphenylphosphine osmium(II) ([OsA C H T U N G T R E N N U N G (bpftz) 2 A C H T U N G T R E N N U N G (PPhMe 2 ) 2 ], OS1) [18] as dopants (Scheme 2). To improve the hole injection from the anode, poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS) was spun onto the precleaned ITO substrate to form a 30 nm thick polymer buffer layer.…”

Indolo[3,2‐b]carbazole‐based poly(arylene ethynylene)s through Sonogashira coupling for optoelectronic and sensing applications

“…The two nitrogen atoms in ICZs are ex situ to each other in the carbazole fragment yielding an electron‐donating character, rigid and coplanar structure with a more extended conjugation, and higher charge carrier mobility compared to carbazole. Their high glass transition temperatures offer high thermal and structural stability in ambient conditions …”