Abstract
Three fused polycyclic aryl fragments, namely, naphthyl, methoxynaphthyl, and pyrenyl have been used to construct blue-emissive phenanthroimidazole-functionalized target molecules, i.e., 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazole (1), 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(1-methoxynaphthalen-4-yl)-1H-phenanthro[9,10-d]imidazole (2), and 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-(pyren-10-yl)-1H-phenanthro[9,10-d]imidazole (3). The up-conversion of triplets to singlets via a triplet–triplet annihilation (TTA) process is dominant in these compounds due to 2ET1 > ES1. The pyrenyl dihydrobenzodioxin phenanthroimidazole (3)-based nondoped OLED exhibits blue emission (450 nm) with CIE (0.15, 0.14), a luminance of 53 890 cd m−2, power efficiency of 5.86 lm W−1, external quantum efficiency of 5.30%, and current efficiency of 6.90 cd A−1. The efficient device performance of pyrenyl dihydrobenzodioxin phenanthroimidazole is due to the TTA contribution to the electroluminescent process.
Highlights
Ever since the dawn of organic light-emitting diodes (OLEDs) Tang and coworkers reported there has been a sustained pursuit to develop high efficient, stable devices for applications capable of generating light of all visible colors.1 the research on OLEDs is far behind in commercial at-panel displays with 100% internal quantum efficiencies (IQE) utilizing green and red electrophosphorescent devices,2 fabricating efficient blue OLEDs is of signi cant interest.3 the majority actual practical blue devices still rely on electroluminescence based on anthracene derivatives4–6 due to the longevity of triplet excitons, efficiencies reaching unity, generation of radiative decay, which lead to quenching at high current density
High Td of dihydrobenzodioxin phenanthroimidazoles indicated the high resistance of the fused aromatic rings on thermolysis; high Tm and Td could enhance the lifetimes of devices,49–51 and the formation of a stable lm can be expected upon device fabrication
Three blue-emissive fused polycyclic aryl phenanthroimidazoles with a side-capping dihydrobenzodioxin moiety showed high thermal device stabilities with efficient device performances
Summary
Ever since the dawn of organic light-emitting diodes (OLEDs) Tang and coworkers reported there has been a sustained pursuit to develop high efficient, stable devices for applications capable of generating light of all visible colors. the research on OLEDs is far behind in commercial at-panel displays with 100% internal quantum efficiencies (IQE) utilizing green and red electrophosphorescent devices, fabricating efficient blue OLEDs is of signi cant interest. the majority actual practical blue devices still rely on electroluminescence based on anthracene derivatives due to the longevity of triplet excitons, efficiencies reaching unity, generation of radiative decay (kr), which lead to quenching at high current density. The majority actual practical blue devices still rely on electroluminescence based on anthracene derivatives due to the longevity of triplet excitons, efficiencies reaching unity, generation of radiative decay (kr), which lead to quenching at high current density. It is desirable to incorporate the bulky side-capped dihydrobenzodioxin at the imidazole nitrogen to reduce the packing between the molecules, which limits emission quenching. This can enhance the stability of blue emission and improve the quantum efficiency.. Since a pyrenyl substituent at the imidazole carbon (C25) of phenanthroimidazole can extend p-conjugation, exhibit efficient electronic properties, and provide effective steric hindrance in the interchromophore packing and TTA contribution, the results showed enhanced quantum efficiency
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