The imminent global energy crisis and continuing inefficient energy utilization are driving the development of smart energy-efficient devices for display and lighting applications. Energy-efficient organic light-emitting diodes (OLEDs) are considered one of the most competitive candidates for next-generation smart displays and particularly for future energy-saving lighting sources. Recently, much effort has been devoted to attempts to generate white OLEDs comprising both fluorescent and phosphorescent materials. Efficient blue-emitting materials are extremely essential for the commercialization of white OLEDs and play a vital role in energy-efficient solid-state lighting and smart display devices. The molecular designing of efficient deep-blue materials is limited due to their intrinsic wide bandgap, poor carrier charge balance, and low efficiency in the solid state. In recent decades, phenanthroimidazole (PI)-based materials have attracted tremendous interest (due to the ease of their chemical/structural modification at the N1 and C2 positions) to produce efficient deep-blue OLEDs (satisfying the color purity criteria given by the National Television System Committee (NTSC)) (CIE: 0.14, 0.08) and European Broadcasting Union (EBU) (CIE: 0.15, 0.06). This review mainly focuses on the design of PI-based blue/deep-blue emitting materials and their applications in OLEDs. Here at first, some of the PI-based blue-fluorescence emitters endowed with unipolar and bipolar-transporting abilities are comprehensively reviewed. Then attention is focused on the typical PI-based host materials for phosphorescent OLEDs. Finally, PI-based hybridized local and charge-transfer (HLCT) active fluorescent emitters are presented in brief. The rational molecular design concepts and general synthetic routes for PI-based materials are briefly discussed.

Recent development of phenanthroimidazole-based fluorophores for blue organic light-emitting diodes (OLEDs): an overview

A series of bipolar phenanthroimidazole derivatives, TTP-TPI, DPT-TPI, and DPF-TPI, were designed and synthesized by incorporating polyaromatic hydrocarbon groups to phenanthroimidazole through a phenyl bridge. The bulky polyaromatic hydrocarbon units endow the molecules with high glass-transition temperatures, nonplanar twisty structures which reduce molecular aggregations. The bipolar transporting natures of these materials are demonstrated by single-carrier devices with supported of theoretical calculations. Nondoped organic light-emitting devices (OLEDs) using these phenanthroimidazole derivatives as emitters show blue-violet to sky-blue emissions with Commission Internationale de l’Eclairage (CIE) coordinates of (0.16, 0.05) for TTP-TPI, (0.16, 0.07) for DPT-TPI, and (0.17, 0.24) for DPF-TPI. The TTP-TPI-, DPT-TPI-, and DPF-TPI-based nondoped devices show impressive external quantum efficiencies (EQE) of 5.02, 5.25, 4.85%, respectively (corresponding current efficiencies: 2.10, 3.13, and 8.41 cd/A). ...

Bipolar Phenanthroimidazole Derivatives Containing Bulky Polyaromatic Hydrocarbons for Nondoped Blue Electroluminescence Devices with High Efficiency and Low Efficiency Roll-Off

Organic light‐emitting diodes (OLEDs) are the most successful product of organic electronics in the market and continually receive attention from scientific and industrial communities. Imidazoles have been extensively investigated for OLED applications, and demonstrated their versatility in molecular design for different functions. This review presents a summary of recent studies on imidazole (including imidazole derived moieties) derivatives, with special focus on discussing various molecular design tactics, for applications as electron‐transporting materials, emitters, and host materials in OLEDs. At last, perspectives and challenges regarding to imidazole semiconductors for electroluminescence applications are also discussed.

Organic Light-Emitting Diodes Based on Imidazole Semiconductors

A significant improvement of the properties of redox catalysts based on the triarylimidazole framework can be achieved with a simple structural modification. By linking the ortho-carbons of the aromatics positioned at C-4 and C-5, a fused framework is generated, removing the distortion from planarity and enhancing the influence of the substituents on the redox properties. This modification leads not only to a much broader range of available redox potentials for the resulting phenanthro[9,10-d]imidazoles but also to improved stability of the corresponding radical cation. These concepts were verified with eight new phenanthro[9,10-d]imidazole derivatives, using cyclic voltammetry and DFT calculations. For this purpose, an optimized and general synthetic route to the desired compounds was developed. An excellent linear correlation of the calculated effective ionization potentials with the experimental oxidation potentials was obtained, allowing for an accurate prediction of oxidation potentials of derivative...

Optimizing Electron Transfer Mediators Based on Arylimidazoles by Ring Fusion: Synthesis, Electrochemistry, and Computational Analysis of 2-Aryl-1-methylphenanthro[9,10-d]imidazoles

2-(2′-Hydroxyphenyl)benzoxazole (HBO) and 2-(2′-hydroxyphenyl)benzothiazole (HBT) reacted with triphenylborane produced two rigid π-conjugated fluorescent cores 1 (BPh2(BOZ), BOZ = 2-(benzo[d]oxazol-2-yl)phenol) and 2 (BPh2(BTZ), BTZ = 2-(benzo[d]thiazol-2-yl)phenol). Comparisons of photophysical properties and calculations between para- and meta-diphenylamine-substituted derivatives 5 (BPh2(para-NPh2-BTZ)) and 7 (BPh2(meta-NPh2-BTZ)) demonstrated that functionalization at the para-position of the rigid core is effective in tuning the electronic structure and hence the photophysical properties of this type of boron-chelate complex. Simple modification of these frameworks by introducing various amine groups at the para-position allows the synthesis of strongly fluorescent materials 3 (BPh2(para-Cz-BTZ), Cz = 9H-carbazol-9-yl), 4 (BPh2(para-NPh2-BOZ), NPh2 = diphenylamino), 5, and 6 (BPh2(para-NMe2-BTZ), NMe2 = dimethylamino). The emission colors of these newly synthesized complexes together with the parent complexes 1 and 2 covered a wide range from deep blue to saturated red in both solution and the solid state. Crystal structure analysis discloses that two phenyl groups attached to the boron atom effectively keep the luminescent ring-fused π-conjugated skeletons apart, making these fluorophores highly emissive in solid forms (ΦF = 0.36–0.71). Organic light-emitting diodes employing these boron complexes as emitters not only keep the full-color tunable emission feature but also show high electroluminescent (EL) performance; for instance, the greenish-blue device based on 2 showed the highest efficiency of 7.8 cd A−1 and the yellow light-emitting device based on 4 exhibited the highest brightness (31 220 cd m−2) among the boron-containing emitters reported so far.

/pdf/construction-of-full-color-tunable-and-strongly-emissive-1z2r5b94p9.pdf

Construction of full-color-tunable and strongly emissive materials by functionalizing a boron-chelate four-ring-fused π-conjugated core

Four phenanthroimidazole derivatives (a: 1,2-diphenyl-1H-phenanthro[9,10-d]imidazole; b: 2-phenyl-1-p-tolyl-1H-phenanthro[9,10-d]imidazole; c: 1-phenyl-2-p-tolyl-1H-phenanthro[9,10-d]imidazole; d: 1,2-di-p-tolyl-1H-phenanthro[9,10-d]imidazole) were synthesized and their single crystal structures, photophysical, electrochemical and mobility properties were carefully studied. Taking advantage of the thermal stability and the hole transporting (HT) ability, the highly efficient Alq3-based organic light-emitting diodes (OLEDs) have been achieved by employing the compounds a–d as a functional layer between NPB (4,4-bis(N-(1-naphthyl)-N-phenylamino)biphenyl) and Alq3 (tris(8-hydroxyquinoline)aluminium) layers. For the device of [ITO/NPB/d/Alq3/LiF/Al], a maximum luminous efficiency (LE) of 8.1 cd A−1 was obtained with a maximum brightness of 65130 cd m−2, which exhibited much higher efficiency compared to the device with structure of [ITO/NPB/Alq3/LiF/Al]. The results demonstrated not only an alternative idea to design novel HT materials, but also a convenient way to improve the performance of the NPB/Alq3-based devices by introduction of a suitable organic buffer layer.

Phenanthroimidazole-derivative semiconductors as functional layer in high performance OLEDs

As a promising anode candidate, silicon (Si) nanoparticles have been widely studied for use in lithium ion batteries. However, Si nanoparticles suffer from the disadvantage of volume expansion during lithiation/delithiation, which leads to irreversible capacity decrease. In this work, perlite is utilized to prepare Si nanoparticles via magnesiothermic reduction. To alleviate the volume expansion of Si nanoparticles, a nanoporous carbon is prepared to coat Si nanoparticles using chitosan (C) as the carbon source and zinc chloride (Z) as the pore former. TEM micrographs show that the porous carbon with mesoporous size has formed and coated the surface of Si nanoparticles. The prepared carbon coated Si sample (Z-C@Si-5 contains 5 times the mass ratio of Z to C) exhibits suitable pore volume (0.576 cm3 g−1) and pore size (4–6 nm), as well as excellent specific surface area (418.315 m2 g−1) The obtained Z-C@Si-5 also shows promising electrochemical performance with a reversible capacity of 2064.11 mA h g−1 at 0.2C and 847.32 mA h g−1 at 4C, as well as a high capacity retention. The promising electrochemical performance originated from the nanoporous carbon coating, which not only effectively alleviated the volume expansion problem of Si, but also provided a rapid transport channel of lithium ions through its nanoporous structure.

Silicon nanoparticles coated with nanoporous carbon as a promising anode material for lithium ion batteries

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Phenanthroimidazole-derivative semiconductors as functional layer in high performance OLEDs

Silicon nanoparticles coated with nanoporous carbon as a promising anode material for lithium ion batteries