Facile Synthesis of Highly Efficient Lepidine‐Based Phosphorescent Iridium(III) Complexes for Yellow and White Organic Light‐Emitting Diodes

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506

336

Due to the characteristics of optical rotation, selective emission of polarized light, and circular dichroism, circularly polarized luminescent materials have aroused extensive attentions, and they have exhibited wide optoelectronic applications, such as optical data storage, liquid crystal display, and backlights in 3D displays. Here, the research progress of circularly polarized luminescent materials for organic optoelectronic devices is summarized. First, the definition and measurement of the circularly polarized light, such as optical rotatory dispersion, circular dichroism, and circularly polarized luminescence, are systematically introduced. Subsequently, the design strategies for various kinds of circularly polarized luminescent materials, including luminescent lanthanide and transition‐metal complexes, small organic luminophores, conjugated polymers, supramolecules, and liquid crystals are summarized. These materials exhibit circularly polarized luminescence with different magnitudes of luminescence dissymmetry values (glum). They are further applied in optoelectronic devices with excellent performance, and the influence factors on the glum values of these materials are presented in detail. Finally, the current opportunities and challenges in this rapidly growing research field are discussed systematically. The circularly polarized luminescent materials with large glum and high luminescence efficiency are very promising for applications in organic optoelectronic fields.

Section: Phosphorescent Transition‐metal Complexesmentioning

confidence: 99%

Recent Progress on Circularly Polarized Luminescent Materials for Organic Optoelectronic Devices

Han

Guo

et al. 2018

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506

336

“…Phosphorescent transition‐metal complexes have played the vital role in the rapid development of OLEDs, because they can harvest both singlet and triplet excitons to achieve an internal quantum efficiency of 100% owing to the highly efficient spin‐orbit coupling effect induced by heavy‐metal atoms . For example, noble metal‐based phosphors including iridium(III) complexes, platinum(II) complexes, and gold(III) complexes have been widely used in phosphorescent OLEDs (PhOLEDs). However, these noble metals suffer from the low abundance and high cost.…”

Section: Key Performance Of the Devices A–cmentioning

confidence: 99%

Designing Highly Efficient Phosphorescent Neutral Tetrahedral Manganese(II) Complexes for Organic Light‐Emitting Diodes

Qin

Tao

Gao

et al. 2018

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coupling effect induced by heavy-metal atoms. [5,6] For example, noble metal-based phosphors including iridium(III) complexes, [7][8][9][10][11][12][13][14][15][16] platinum(II) complexes, [17][18][19][20] and gold(III) complexes [21,22] have been widely used in phosphorescent OLEDs (PhOLEDs). However, these noble metals suffer from the low abundance and high cost. Hence, the relatively abundant, lowcost, and low-toxic phosphorescent metal complex have been drawing great interests for PhOLEDs.Recent explorations of phosphorescent manganese(II) complexes appear to be a new and attractive alternative toward highly efficient PhOLEDs. The manganese(II) complexes display strong photoluminescence in solid state originating from the metal-centered d-d ( 4 T 1 (G) → 6 A 1 ) radiative transition. [23][24][25] The well-known green light-emitting manganese(II) complexes are ionic compounds consisting of organic cations and inorganic tetrahalogenomanganate(II) anions. [26,27] Attributed to their excellent solid-state photophysical properties, this kind of organic-inorganic hybrid complexes have exhibited promising optoelectronic applications. For example, Chen and co-workers have realized the solution-processed PhOLEDs based on the ionic tetrabromide manganese(II) complex ((Ph 4 P) 2 (MnBr 4 )) as an emitting dopant, the external quantum efficiency (EQE) of this device can reach 9.6% for the doped OLEDs. [28] However, the ionic manganese(II) complexes often suffer from low stability and can be easily hydrolyzed Phosphorescent transition-metal complexes have played the vital role in the rapid development of organic light-emitting diodes (OLEDs) as the most promising candidates for next-generation flat-panel display and solid-state lighting techniques. In this work, novel and low-cost phosphorescent neutral tetrahedral manganese(II) complexes (DBFDPO-MnX 2 , X = Br, or Cl) based on dibenzofuran-based phosphine oxide derivative as ligand are designed and synthesized. The manganese(II) complexes exhibit intense green phosphorescence with high photoluminescence quantum yields (PLQYs) of as high as 81.4% (DBFDPO-MnBr 2 ). Using complex DBFDPO-MnBr 2 as dopant, a green OLED with current efficiency (CE max ) of 35.47 cd A −1 , power efficiency (PE max ) of 34.35 lm W −1 , and external quantum efficiency (EQE max ) of 10.49% is fabricated. Interestingly, red exciplex emission is also observed in electroluminescence, arising from the interaction between the host materials (bis(2-(2-hydroxyphenyl)-pyridine)beryllium (Bepp 2 ) or 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBi)) and the dopant (DBFDPO-MnBr 2 ).The exciplex-based red OLED in this study exhibits the maximum CE and PE reaching 18.64 cd A −1 and 17.92 lm W −1 , respectively, which are among the up-to-date highest values for exciplex-based red OLEDs. Beneficial from the exciplex, it has the great potential to broaden the electroluminescent spectra with manganese(II) complex. Phosphorescent OLEDsThe ORCID identification number(s) for the author(s) of this article can be fou...

“…Organic persistent room‐temperature phosphorescence (OPRTP) from long‐lived triplet states in the ambient atmosphere is significant to the advanced optoelectronic technologies, such as organic light‐emitting diodes, sensing, bioimaging, and anti‐counterfeiting applications . Pure organic OPRTP materials are more attractive compared to the transition metal or rare earth‐based phosphorescent materials owing to their low production cost, easy synthesis, low toxicity, and good flexibility .…”

Section: Introductionmentioning

confidence: 99%

Achieving Dual Persistent Room‐Temperature Phosphorescence from Polycyclic Luminophores via Inter‐/Intramolecular Charge Transfer

Guo

Qin

et al. 2019

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bioimaging, [3] and anti-counterfeiting applications. [4] Pure organic OPRTP materials are more attractive compared to the transition metal or rare earth-based phosphorescent materials owing to their low production cost, easy synthesis, low toxicity, and good flexibility. [5] However, OPRTP is rare in pure organic molecules because of the forbidden transition from singlet to triplet excited states. The reported metal-free OPRTP materials are usually substituted with aromatic carbonyl groups [6] or heavy atoms [7] to facilitate the intersystem crossing (ISC) process, while crystallization, [8] host-guest interaction, [9] and polymer doping [10] are utilized to suppress the nonradiative decay and stabilize the triplet states.Solid-state phosphorescence is highly dependent on molecular stacking, such as aggregation-caused quenching. [11] Recently, OPRTP has been observed in H- [8a] or J-aggregates, [12] while the influence of T-shaped (edge-to-face) arrangement on phosphorescence has been rarely discussed. Published work mainly focused on the stabilization of triplet excited states by molecular packing, but packing-induced intermolecular charge transfer received less attention in OPRTP materials although it strongly affected ISC efficiency and the energy gap (ΔE ST ) between singlet and triplet excited states. [3c,13] Polycyclic π-conjugated compounds, such as indolo[3,2-b] carbazoles (ICZs) and their analogues, are important organic semiconductors, which have been widely used in organic optoelectronic fields, such as organic field-effect transistors and photovoltaic cells, owing to their excellent carrier transporting properties. [14] In this work, 6,12-diphenyl-5,6,11,12tetrahydroindolo[3,2-b]carbazole (Ben-H, Figure 1), one of the ICZ analogues, unexpectedly exhibited OPRTP after the cease of UV light irradiation. Unlike most reported OPRTP materials, there were no commonly used groups such as aromatic carbonyl groups or heavy atoms in Ben-H. Based on the energy level diagram and single-crystal structure of Ben-H, we hypothesized that charge transfer (CT) played a dominant role in persistent emission (Figure 2). In the isolated molecular state, intramolecular charge transfer (ICT) from the indole rings to the benzene rings gave rise to the ISC process with narrow ΔE ST energy gap, while in the dimers, T-shaped CH···π interactions induced Organic persistent room-temperature phosphorescence (OPRTP) materials show great prospects in optoelectronic and biomedical applications, such as display, anti-counterfeiting, sensing, and bioimaging. However, the reported OPRTP material systems are relatively rare, and it is a challenge to achieve the tunability of OPRTP. In this work, a series of polycyclic luminophores are developed based on an indole derivative (6,12-diphenyl-5,6,11,12tetrahydroindolo[3,2-b] carbazole, Ben-H) as the structural skeleton. These compounds unexpectedly exhibit dual OPRTP at 442 to 623 nm with lifetimes spanning from 2 to 759 ms. Experimental data and theoretical calculations suggest th...