Pyridine-containing phenanthroimidazole electron-transport materials with electron mobility/energy-level trade-off optimization for highly efficient and low roll-off sky blue fluorescent OLEDs

Abstract

By incorporating the pyridine ring to the different position of rigid phenanthroimidazole skeleton, three new pyridine-containing phenanthroimidazole derivatives, 1-phenyl-2-(4-(pyridin-3-yl)phenyl)-1H-phenanthro[9,10-d]imidazole(CPI-p3Py), 2-phenyl-1-(4-(pyridin-3-yl)phenyl)-1H-phenanthro[9,10-d]imidazole(NPI-p3Py) and 1,2-bis(4-(pyridin-3-yl)phenyl)-1H-phenanthro[9,10-d]imidazole(CNPI-p3Py), were designed and synthesized as electron-transport materials (ETMs). Their photophysical properties, energy levels and electron mobilities can be readily regulated through changing the connecting position. Through optimizing electron mobility and energy levels trade-offs, CNPI-p3Py exhibits not only lower-lying HOMO/LUMO energy levels, but also relatively higher electron mobility around 10 -3 cm 2 V -1 s -1 , which is 2-fold greater than that of the widely used material BPhen. More interesting, the blue fluorescent OLEDs with CPI-p3Py or CNPI-p3Py as an electron-transporting layer (ETL) exhibited superior performance compared to that using Bphen, remarkably lowering the driving voltage and improving efficiencies. In particular, the device with CNPI-p3Py as an ETL showed a maximum current efficiency of 15.17 cd A -1 , a maximum power efficiency of 10.65 lm W -1 , a maximum external quantum efficiency (EQE) of 7.75% and low efficiency roll-off even at an illumination-relevant luminance of 10,000 cd m -2 by the efficient utilization of the up-conversion of a triplet excited state, which are among the most efficient ETMs and proposes a new strategy for the molecular design of high-performance ETMs.

Derivatives of Cyanonaphthyl-Substituted Phenanthroimidazole as Blue Emitters for Nondoped Organic Light-Emitting Diodes

“…This is ascribed to the newly generated CT owing to conjugation among the donors (triphenylamine or carbazole) and acceptor (phenanthroimidazole) as the donor moieties attached to the para carbon of thiaphenyl phenanthroimidazole. 51 New-born emitters exhibit similar absorption (sol/film) 254 (ε max = 39 370 cm –1 M –1 ), 308/252, 316 (TPNCN-TPA), and 250 (ε max = 40 000 cm –1 M –1 ), 301/246, 295 nm (TPNCN-Cz) because the core fragment is not different. The absorption from 301 and 308 nm is due to intramolecular charge transfer 52,53 from the donor (carbazole/triphenylamine) to acceptor (phenanthrimidazole).…”

“…In addition, the absorption at 300–340 nm is attributed to intramolecular CT from the donor to acceptor unit. 51 Compared with parent compounds bis phenanthrimidazoles (NPIBN, CNPIBP, and CNPIBN), D−π–A materials (TPNCN-TPA and TPNCN-Cz) show larger absorption intensity. This is ascribed to the newly generated CT owing to conjugation among the donors (triphenylamine or carbazole) and acceptor (phenanthroimidazole) as the donor moieties attached to the para carbon of thiaphenyl phenanthroimidazole.…”

Effective Energy Transfer for Green, Orange, and Red Phosphorescent Organic Light‐Emitting Diodes Based on a Bipolar Deep‐Blue Emitter with Low Efficiency Roll‐Off at High Brightness

“…[ 23 ] The weak shoulder at ≈363 nm should be assigned to the π – π * electronic transition of PI unit. [ 24 ] Optical bandgap ( E g ) is calculated from the threshold of its absorptions to be 3.18 eV, showing the potential to achieve deep‐blue emission in OLEDs.…”

Benzimidazole–phosphine oxide hybrid electron transporters for unilateral homogeneous phosphorescent organic light-emitting diodes with enhanced power efficiency

“…All the developed electron-transport materials were purified by silica gel chromatography and then repeated thermal gradient vacuum sublimation before characterization and device fabrication. The molecular structures were confirmed by 1 H NMR, 13 C NMR and mass spectroscopy. The detailed This journal is © The Royal Society of Chemistry 2015 synthetic methods and analysis are described in the Experiment section.…”

“…Therefore, the development of electron-transport materials (ETMs) with high electron mobility and appropriate energy levels is urgent. [11][12][13] In recent years, the diphenylphosphine oxide (DPPO) group has been widely used as a unique electroactive insulating linkage. 14,15 It has been reported that its strong electron-withdrawing inductive effect can polarize molecules and enhance electron transport properties.…”