Optical and electroluminescent performances of dihydrobenzodioxin phenanthroimidazoles based blue-emitting materials

Robust luminogens as cutting-edge tools for efficient light emission in recent decades

Blue luminogens play a vital role in white lighting and potential metal-free fluorescent materials and their high-lying excited states contribute to harvesting triplet excitons in devices. However, in TADF-OLEDs (ΔEST < 0.1 eV), although T1 excitons transfer to S1via RISC with 100% IQE, the longer lifetime of blue TADF suffers from efficiency roll-off (RO). In this case, hybridized local and charge transfer (HLCT) materials have attracted significant interest in lighting owing to their 100% hot exciton harvesting and enhanced efficiency. Both academics and industrialists widely use the HLCT strategy to improve the efficiency of fluorescent organic light-emitting diodes (FOLEDs) by harvesting dark triplet excitons through the RISC process. Aggregation-induced emissive materials (AIEgens) possess tight packing in the aggregation state, and twisted AIEgens with HLCT behaviour have a shortened conjugation length, inducing blue emission and making them suitable candidates for OLED applications. TTA-OLEDs are used in commercial BOLEDs because of their moderate efficiency and reasonable operation lifetime. In this review, we discuss the devices based on TTA fluorophores, TADF fluorophores, HLCT fluorophores, AIEgens and HLCT-sensitized fluorophores (HLCT-SF), which break through the statistical limitations.

Fabrication of high performance based deep-blue OLED with benzodioxin-6-amine-styryl-triphenylamine and carbazole hosts as electroluminescent materials

The present study reports synthesis of phenathroimidazole derivatives structures following donor-acceptor relation for high performance deep-blue light emitting diodes. Herein, methyl substituted benzodioxin-6-amine phenanthroimidazoles Cz-SBDPI and TPA-SBDPI derivatives that provide the blue light were designed and synthesized. These Cz-SBDPI and TPA-SBDPI show higher glass transition (Tg) temperatures of 199 and 194 °C and demonstrate enhanced thermal properties. Apart from enhanced thermal stability these compounds also exhibit superior photophysical, electrochemical and electroluminescent properties. The non-doped carbazole based device display improved electroluminescent performances than those of TPA-based devices. The strong orbital-coupling due to decreased energy barrier between Cz-SBDPI transitions result in deep blue emission with CIE-0.15, 0.06. For non-doped Cz-SBDPI device; high L (brightness):12,984 cd/m2; ηc (current efficiency): 5.9 cd/A; ηp (power efficiency): 5.7 lm/W and ηex (external quantum efficiency): 6.2% was observed. The results show that the D-A emitters can serve as simple but also as an effective approach to devise cheap electroluminescent materials that has high efficiency and can serve as OLED devices.

Organic fluorescent compounds based on phenanthroimidazole: A review of highlight studies

Organic compounds containing phenanthroimidazole, and its optical, thermal, chemical, and high fluorescence, have drawn the interest of numerous researchers. Phenanthroimidazole derivatives are appealing for various applications due to these characteristics. This research provides a summary of the general information contained in studies on the synthesis, characterization, photophysical characteristics, and possible applications of phenanthroimidazole derivative compounds. The focus of this study revolves around the topic of utilization in technological fields such as sensors, solar cells, optical brighteners, and organic light-emitting diodes, and covers significant studies on mentioned topics. We anticipate that this study will provide an outline for researchers aiming to further examine fluorescent organic compounds for technological innovations. Furthermore, we anticipate that this research will be crucial in developing long-term high-organic compounds for optoelectronic devices.

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

New multifunctional blue-emissive materials with superior thermal properties, viz., 4,4'-bis(1-(4-naphthyl)-1H-phenanthro[9,10-d]imidazol-2-yl)binaphthyl (NPIBN), 4,4'-bis(1-(4-cyanonaphthyl)-1H-phenanthro[9,10-d]imidazol-2-yl)biphenyl (CNPIBP), and 4,4'-bis(1-(4-cyanonaphthyl)-1H-phenanthro[9,10-d]imidazol-2-yl)binaphthyl (CNPIBN) have been synthesized. The said molecules show high photoluminescence quantum yield (Φs/f: NPIBN-0.75/0.68, CNPIBP-0.85/0.76, and CNPIBN-0.90/0.88). The fabricated nondoped/doped device with CNPIBN/4,4'-bis(carbazol-9-yl)biphenyl: CNPIBN display maximum efficiencies (ηex 4.96/5.4%; ηc 7.46/7.56 cd A-1; ηp 6.85/6.91 lm W-1) at low turn-on voltage (3.5/3.8 V). Nondoped devices based on D-π-A architecture, 4-(2-(5-(9H-carbazol-9-yl)thiophen-2-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile exhibit maximum efficiencies (ηex 2.32%; ηc 4.00 cd A-1; ηp 3.42 lm W-1) compared to 4-(2-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (ηex 2.01%; ηc 3.89 cd A-1; ηp 3.15 lm W-1).

Tailoring the molecular design of twisted dihydrobenzodioxin phenanthroimidazole derivatives for non-doped blue organic light-emitting devices

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 2E_T1 > E_S1. 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.

Efficient blue emitters, 1-(2,3-dihydrobenzodioxinyl)-2-naphthylphenanthroimidazole, 1-(2,3-dihydrobenzodioxinyl)-2-methoxynaphthylphenanthroimidazole and 1-(2,3-dihydrobenzodioxinyl)-2-pyrenylphenanthroimidazole have been reported.