Stepwise Toward Pure Blue Organic Light-Emitting Diodes by Synergetically Locking and Shielding Carbonyl/Nitrogen-Based MR-TADF Emitters

Deep-blue multi-resonance (MR) emitters with stable and narrow full-width-at-half-maximum (FWHM) are of great importance for widening the color gamut of organic light-emitting diodes (OLEDs). However, most planar MR emitters are vulnerable to intermolecular interactions from both the host and guest, causing spectral broadening and exciton quenching in thin films. Their emission in the solid state is environmentally sensitive, and the color purity is often inferior to that in solutions. Herein, a molecular design strategy is presented that simultaneously narrows the FWHM and suppresses intermolecular interactions by combining intramolecular locking and peripheral shielding within a carbonyl/nitrogen-based MR core. Intramolecularly locking carbonyl/nitrogen-based bears narrower emission of 2,10-dimethyl-12,12-diphenyl-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-4,8(12H)-dione in solution and further with peripheral-shielding groups, deep-blue emitter (12,12-diphenyl-2,10-bis(9-phenyl-9H-fluoren-9-yl)-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine-4,8(12H)-dione, DPQAO-F) exhibits ultra-pure emission with narrow FWHM (c.a., 24 nm) with minimal variations (∆FWHM ≤ 3 nm) from solution to thin films over a wide doping range. An OLED based on DPQAO-F presents a maximum external quantum efficiency (EQEmax) of 19.9% and color index of (0.134, 0.118). Furthermore, the hyper-device of DPQAO-F exhibits a record-high EQEmax of 32.7% in the deep-blue region, representing the first example of carbonyl/nitrogen-based OLED that can concurrently achieve narrow bandwidth in the deep-blue region and a high electroluminescent efficiency surpassing 30%.

Molecular Engineering of Perylene Diimide Polymers with a Robust Built-in Electric Field for Enhanced Solar-Driven Water Splitting

The built-in electric field of the polymer semiconductors could be regulated by the dipole moment of its building blocks, thereby promoting the separation of photogenerated carriers and achieving efficient solar-driven water splitting. Herein, three perylene diimide (PDI) polymers, namely oPDI, mPDI and pPDI, are synthesized with different phenylenediamine linkers. Notably, the energy level structure, light-harvesting efficiency, and photogenerated carrier separation and migration of polymers are regulated by the orientation of PDI unit. Among them, oPDI enables a large dipole moment and robust built-in electric field, resulting in enhanced solar-driven water splitting performance. Under simulated sunlight irradiation, oPDI exhibits the highest photocurrent of 115.1 μA cm-2 for photoelectrochemical oxygen evolution, which is 11.5 times that of mPDI, 26.8 times that of pPDI and 104.6 times that of its counterparts PDI monomer at the same conditions. This work provides a strategy for designing polymers by regulating the orientation of structural units to construct efficient solar energy conversion systems.

Thiyl Radical Trapped by Cobalt Catalysis: An Approach to Markovnikov Thiol-Ene Reaction

In the presence of a thiyl radical species, the catalytic Markovnikov thiol-ene reaction is challenging because it prefers to proceed via a radical pathway, thereby leading to anti-Markovnikov selectivity. In this work, a rare example of thiyl radical engaged in Markovnikov thiol-ene reaction enabled by cobalt catalysis is reported. This protocol features the avoidance of unique oxidants, exclusive regioselectivity, and broad substrate scope. Scalable synthesis and late-stage modification of complex molecules demonstrate the practicability of the protocol.

Nitrogen-doped carbon dots for efficient deep-blue light-emitting diodes with CIE closely approaching the HDTV standard color Rec.BT.709

Here, we demonstrate deep-blue carbon dots (CDs) with luminescence centered at 415 nm and PLQY exceeding 60% via nitrogen doping. A bright and high-color-purity CDs-based light-emitting diode (CLED) is achieved with an external quantum efficiency (EQE) of 1.74%, a maximum luminance of 1155.0 cd m^-2, and a colour coordinate (0.16, 0.08) closely approaching the HDTV standard color Rec.BT.709 (0.15, 0.06) specification.

Interface-Engineered Ni-Coated CdTe Heterojunction Photocathode for Enhanced Photoelectrochemical Hydrogen Evolution

Photoelectrochemical (PEC) water splitting for hydrogen production using the CdTe photocathode has attracted much interest due to its excellent sunlight absorption property and energy band structure. This work presents a study of engineered interfacial energetics of CdTe photocathodes by deposition of CdS, TiO₂, and Ni layers. A heterostructure CdTe/CdS/TiO₂/Ni photocathode was fabricated by depositing a 100-nm n-type CdS layer on a p-type CdTe surface, with 50 nm TiO₂ as a protective layer and a 10 nm Ni layer as a co-catalyst. The CdTe/CdS/TiO₂/Ni photocathode exhibits a high photocurrent density (J_ph) of 8.16 mA/cm² at 0 V versus reversible hydrogen electrode (V_RHE) and a positive-shifted onset potential (E_onset) of 0.70 V_RHE for PEC hydrogen evolution under 100 mW/cm² AM1.5G illumination. We further demonstrate that the CdTe/CdS p-n junction promotes the separation of photogenerated carriers, the TiO₂ layer protects the electrode from corrosion, and the Ni catalyst improves the charge transfer across the electrode/electrolyte interface. This work provides new insights for designing noble metal-free photocathodes toward solar hydrogen development.

Minisci reaction of heteroarenes and unactivated C(sp3)-H alkanes via a photogenerated chlorine radical

Here, an efficient Minisci reaction of heteroarenes and unactivated C(sp³)-H alkanes was achieved using an inexpensive FeCl₃ as a photocatalyst. The photogenerated chlorine radical contributed to the HAT of C-H and subsequently initiated this reaction. Surprisingly, salt water and even seawater can act as a chlorine radical source, which provided an enlightening idea for future organic synthesis methods.

Regulable cross-coupling of alcohols and benzothiazoles via a noble-metal-free photocatalyst under visible light

Here, we realize a regulable cross-coupling reaction using alcohols as alkylating reagents to functionalize benzothiazoles. Two types of cross-coupling products are obtained with the highest isolated yields of up to 99% and 90% for alkyl- and acetyl-derived benzothiazoles, respectively, which opens up a broad research prospect for expanding alcohols as alkylating reagents.

Deep-Blue OLEDs with Rec.2020 Blue Gamut Compliance and EQE Over 22% Achieved by Conformation Engineering

To achieve high-efficiency deep-blue electroluminescence satisfying Rec.2020 standard blue gamut, two thermally activated delayed fluorescent (TADF) emitters are developed: 5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-10,10-diphenyl-5,10-dihydrodibenzo[b,e][1,4]azasiline (TDBA-PAS) and 10-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-9,9-diphenyl-9,10-dihydroacridine (TDBA-DPAC). Inheriting from their parented organoboron multi-resonance core, both emitters show very promising deep-blue emissions with relatively narrow full width at half-maximum (FWHM, ≈50 nm in solution), high photoluminescence quantum yield (up to 92.3%), and short emission lifetime (≤2.49 µs) with fast reverse intersystem crossing (>10⁶ s^-1 ) in doped films. More importantly, replacing the spiro-centered sp³ C atom (TDBA-DPAC) with the larger-radius sp³ Si atom (TDBA-PAS), enhanced conformational heterogeneities in bulky-group-shielded TADF molecules are observed in solution, doped film, and device. Consequently, OLEDs based on TDBA-PAS retain high maximum external quantum efficiencies ≈20% with suppressed efficiency roll-off and color index close to Rec.2020 blue gamut over a wide doping range of 10-50 wt%. This study highlights a new strategy to restrain spectral broadening and redshifting and efficiency roll-off in the design of deep-blue TADF emitters.

Recent Advances in Visible-Light Photoredox Catalysis for the Thiol-Ene/Yne Reactions

Visible-light photoredox catalysis has been established as a popular and powerful tool for organic transformations owing to its inherent characterization of environmental friendliness and sustainability in the past decades. The thiol-ene/yne reactions, the direct hydrothiolation of alkenes/alkynes with thiols, represents one of the most efficient and atom-economic approaches for the carbon-sulfur bonds construction. In traditional methodologies, harsh conditions such as stoichiometric reagents or a specialized UV photo-apparatus were necessary suffering from various disadvantages. In particular, visible-light photoredox catalysis has also been demonstrated to be a greener and milder protocol for the thiol-ene/yne reactions in recent years. Additionally, unprecedented advancements have been achieved in this area during the past decade. In this review, we will summarize the recent advances in visible-light photoredox catalyzed thiol-ene/yne reactions from 2015 to 2021. Synthetic strategies, substrate scope, and proposed reaction pathways are mainly discussed.

External oxidant-free and selective thiofunctionalization of alkenes enabled by photoredox-neutral catalysis

A photoredox approach was reported to realize a highly selective three-component thiohydroxylation, thioalkoxylation and thioamination of vinylarenes towards valuable vicinal S,O- and S,N-disubstituted molecules under mild conditions.

Surface Engineering of Nanoporous Silicon Photocathodes for Enhanced Photoelectrochemical Hydrogen Production

Silicon (Si) is a promising semiconductor material in photoelectrochemical (PEC) H2 evolution due to its advantages of Earth-abundant element, non-toxicity, broad absorption of the solar spectrum, high saturated-current and industrial...

Photoinduced Radical Cascade Cyclization: A Metal-Free Approach to Access Difluoroalkylated Dioxodibenzothiazepines

A simple and mild photoredox catalytic approach to access difluoroalkylated dioxodibenzothiazepines in high regioselectivity via radical cascade cyclization has been described herein. In contrast to previous methods, this strategy does not involve the use of transition-metal catalysts and avoids the potential disadvantages of inevitable toxicity and the tedious removal process of metal catalysts. The commercially available and inexpensive CF₂ precursors, wide substrate scope, and mild reaction conditions demonstrate the practicability of this approach.

Constructing Highly Efficient Blue OLEDs with External Quantum Efficiencies up to 7.5 % Based on Anthracene Derivatives

Acquiring desirable device performance with deep-blue color purity that fulfills practical application requirements is still a challenge. Bipolar fluorescent emitters with hybrid local and charge transfer (HLCT) state may serve to address this issue. Herein, by inserting anthracene core in the deep-blue building blocks, the authors successfully developed two highly twisted D-π-A fluorescent emitters, ICz-An-PPI and IP-An-PPI, featuring different acceptor groups. Both exhibited superb thermal stabilities, high photo luminescent quantum yields and excellent bipolar transport capabilities. The non-doped OLEDs using ICz-An-PPI and IP-An-PPI as the emitting layers showed efficient blue emission with an external quantum efficiency (EQE_max ) of 4.32 % and 5.41 %, and the CIE coordinates of (0.147, 0.180) and (0.149, 0.150), respectively. In addition, the deep blue doped device based on ICz-An-PPI was achieved with an excellent CE_max of 5.83 cd A^-1 , EQE_max of 4.6 % and the CIE coordinate of (0.148, 0.078), which is extremely close to the National Television Standards Committee (NTSC) standard. Particularly, IP-An-PPI-based doped device had better performance, with an EQE_max of 7.51 % and the CIE coordinate of (0.150, 0.118), which was very impressive among the recently reported deep-blue OLEDs with the CIE_y <0.12. Such high performance may be attributed to the hot exciton HLCT mechanism via T₇ to S₂ . Our work may provide a new approach for designing high-efficiency deep-blue materials.

Carbon Dots/α-Fe2O3-Fe3O4 nanocomposite: Efficient synthesis and application as a novel electrochemical aptasensor for the ultrasensitive determination of aflatoxin B1

Developing an effective method for the detection of aflatoxin B1 (AFB1) remains an arduous task due to the high toxicity of AFB1 to a health concern. In this study, a sensitive and reliable electrochemical aptasensor based on carbon dots/α-Fe₂O₃-Fe₃O₄ nanocomposite (CDs/α-Fe₂O₃-Fe₃O₄) is constructed for the determination of AFB1. The CDs have good electrical conductivity and large specific surface areas to improve the aptasensor's sensitivity. The α-Fe₂O₃-Fe₃O₄ can not only improve the catalytic performance of the aptasensor but also have magnetism, which can realize the recovery of CDs/α-Fe₂O₃-Fe₃O₄ to avoid material waste and environmental pollution. This electrochemical aptasensor can achieve a good linear (0.001-100.0 nM) and excellent detection limit (0.5 pM) for the determination of AFB1. In addition, the aptasensor was also applied to determine AFB1 in beer, rice, and peanuts, all results were in good agreement with HPLC, indicating that the electrochemical aptasensor has a broad application prospect.

Photoredox/cobaloxime co-catalyzed allylation of amines and sulfonyl hydrazines with olefins to access α-allylic amines and allylic sulfones

Herein, we reported a dual-catalytic platform for the allylation of amines and sulfonyl hydrazines with olefins to selectively access α-allylic amines and allylic sulfones in good yields by combining photoredox catalysis and cobaloxime catalysis. This strategy avoided the use of a stoichiometric amount of terminal oxidant and the use of pre-functionalized allylic precursors, representing a green and ideal atom- & step-economical process. Good substrate scope and gram-scale synthesis demonstrated the utility of this protocol. Mechanistic studies revealed that a radical process is probably involved in this reaction.

Light-Promoted and Tertiary-Amine-Assisted Hydroxysulfenylation of Alkenes: Selective and Direct One-Pot Synthesis of β-Hydroxysulfides

A light-promoted and tertiary-amine-assisted strategy for efficient hydroxysulfenylation of both electron-rich and electron-deficient alkenes with thiophenols to selectively and directly access β-hydroxysulfides in one pot is described herein. In contrast to the previously reported thiol-oxygen co-oxidation reactions, this simple and sustainable approach features mild reaction conditions, high efficiency, and excellent functional group tolerance.

Multifunctional Materials Serving as Efficient Non-Doped Violet-Blue Emitters and Host Materials for Phosphorescence

Efficient multifunctional materials acting as violet-blue emitters, as well as host materials for phosphorescent OLEDs, are crucial but rare due to demand that they should have high first singlet state (S₁ ) energy and first triplet state (T₁ ) energy simultaneously. In this study, two new violet-blue bipolar fluorophores, TPA-PI-SBF and SBF-PI-SBF, were designed and synthesized by introducing the hole transporting moiety triphenylamine (TPA) and spirobifluorene (SBF) unit that has high T₁ into high deep blue emission quantum yield group phenanthroimidazole (PI). As the results, the non-doped OLEDs based on TPA-PI-SBF exhibited excellent EL performance with a maximum external quantum efficiency (EQE_max ) of 6.76 % and a violet-blue emission with Commission Internationale de L'Eclairage (CIE) of (0.152, 0.059). The device based on SBF-PI-SBF displayed EQE_max of 6.19 % with CIE of (0.159, 0.049), which nearly matches the CIE coordinates of the violet-blue emitters standard of (0.131, 0.046). These EL performances are comparable to the best reported non-doped deep or violet-blue emissive OLEDs with CIEy<0.06 in recent years. Additionally, the green, yellow and red phosphorescent OLEDs with TPA-PI-SBF and SBF-PI-SBF as host materials achieved a high EQE_max of about 20 % and low efficiency roll-off at the ultra-high luminance of 10 000 cd m^-2 . These results provided a new construction strategy for designing high-performance violet-blue emitters, as well as efficient host materials for phosphorescent OLEDs.

Directing-Group-Assisted Markovnikov-Selective Hydrothiolation of Styrenes with Thiols by Photoredox/Cobalt Catalysis

In contrast with the well-developed radical thiol-ene reaction to access anti-Markovnikov-type products, the research on the catalytic Markovnikov-selective hydrothiolation of alkenes is very restricted. Because of the catalyst poisoning of metal catalysts by organosulfur compounds, limited examples of transition-metal-catalyzed thiol-ene reactions have been reported. However, in this work, a directing-group-assisted hydrothiolation of styrenes with thiols by photoredox/cobalt catalysis is found to proceed smoothly to afford Markovnikov-type sulfides with excellent regioselectivity.

Rational Molecular Design of Multifunctional Blue-Emitting Materials Based on Phenanthroimidazole Derivatives

High-performance deep-blue emitters with external quantum efficiencies (EQEs) exceeding 5 % are still scarce in organic light-emitting diodes (OLEDs). In this work, by introducing a [1,2,4]triazolo[1,5-a] pyridine (TP) unit at the N1 position of phenanthroimidazole (PI), two luminescent materials, PTPTPA and PTPTPA, were obtained. Systematic photophysical analysis showed that the TP block is suitable for constructing hybridized local and charge-transfer (HLCT) emitters. Its moderate electron-withdrawing ability and rigid planar structure can enhance the CT component while ensuring color purity. In addition, compared with PTPTPA, the additional phenyl ring of PTPBPTA not only increased the oscillator strength, but also decreased the Stokes shift. TDDFT calculations pointed out facile reverse intersystem crossing processes in PTPTPA from high-lying triplet states to the singlet excited state. A nondoped device based on PTPTPA as emitter showed impressive performance with EQE_max of 7.11 % and CIE coordinates of (0.15, 0.09). At the same time, it was also an efficient host for yellow and red phosphorescent OLEDs. By doping yellow (PPYBA) and red (BTPG) phosphorescent dyes into PTPTPA, a white OLED with a high EQE of 23.85 % was achieved. The successful design of PTPTPA not only provided an optimization choice for OLED emitters, but also demonstrated the empirical rules for the design of multifunctional deep-blue emitters.

Disentangling Multiple Effects on Excited-State Intramolecular Charge Transfer among Asymmetrical Tripartite PPI-TPA/PCz Triads

By utilizing the bipolarity of 1,2-diphenylphenanthroimidazole (PPI), two types of asymmetrical tripartite triads (PPI-TPA and PPI-PCz) were designed with triphenylamine (TPA) and 9-phenylcarbazole (PCz). These triads are deep-blue luminescent materials with a high fluorescence quantum yield of nearly 100 %. To trace the photophysical behaviors of these triads, their excited-state evolution channels and interchromophoric interactions were investigated by ultrafast time-resolved transient absorption and excited-state theoretical calculations. The results suggest that the electronic nature, asymmetrical tripartite structure, and electron-hole distance of these triads, as well as solvent polarity, determine the lifetime of intramolecular charge transfer (ICT). Interestingly, PPI-PCz triads show anti-Kasha ICT, and the charge-transfer direction among the triads is adjustable. For the PPI-TPA triad, the electron is transferred from TPA to PPI, whereas for the PPI-PCz triad the electron is pushed from PPI to PCz. Exploration of the excited-state ICT in these triads may pave the way to design better luminescent materials in the future.

Iron-Catalyzed Regiodivergent Hydrostannation of Alkynes: Intermediacy of Fe(IV)-H versus Fe(II)-Vinylidene

We report an iron system, Cp*Fe(1,2-R₂PC₆H₄X), which controls the Markovnikov and anti-Markovnikov hydrostannation of alkynes by tuning the ionic metal-heteroatom bonds (Fe-X) reactivity. The sequential addition of nBu₃SnH to the iron-amido catalyst (1, X = HN^-, R = Ph) affords a distannyl Fe(IV)-H species responsible for syn-addition of the Sn-H bond across the C≡C bond to produce branched α-vinylstannanes. Activation of the C(sp)-H bond of alkynes by an iron-aryloxide catalyst (2, X = O^-, R = Cy) affords an iron(II) vinylidene intermediate, allowing for gem-addition of the Sn-H to the terminal-carbon producing β-vinylstannanes. These catalytic reactions exhibit excellent regioselectivity and broad functional group compatibility and enable the large-scale synthesis of diverse vinylstannanes. Many new reactions have been established based on such a synthetic Fe-X platform to demonstrate that the initial step of the catalysis is conveniently controlled by the activation of either the tin hydride or the alkyne substrate.

Imidazo[1,2-a]pyridine as an Electron Acceptor to Construct High-Performance Deep-Blue Organic Light-Emitting Diodes with Negligible Efficiency Roll-Off

Two novel bipolar deep-blue fluorescent emitters, IP-PPI and IP-DPPI, featuring different lengths of the phenyl bridge, were designed and synthesized, in which imidazo[1,2-a]pyridine (IP) and phenanthroimidazole (PI) were proposed as an electron acceptor and an electron donor, respectively. Both of them exhibit outstanding thermal stability and high emission quantum yields. All the devices based on these two materials showed negligible efficiency roll-off with increasing current density. Impressively, non-doped organic light-emitting diodes (OLEDs) based on IP-PPI and IP-DPPI exhibited external quantum efficiencies (EQEs) of 4.85 % and 4.74 % with CIE coordinates of (0.153, 0.097) and (0.154, 0.114) at 10000 cd m^-2 , respectively. In addition, the 40 wt % IP-PPI doped device maintained a high EQE of 5.23 % with CIE coordinates of (0.154, 0.077) at 10000 cd m^-2 . The doped device based on 20 wt % IP-DPPI exhibited a higher deep-blue electroluminescence (EL) performance with a maximum EQE of up to 6.13 % at CIE of (0.153, 0.078) and maintained an EQE of 5.07 % at 10000 cd m^-2 . To the best of our knowledge, these performances are among the state-of-the art devices with CIE_y ≤0.08 at a high brightness of 10000 cd m^-2 . Furthermore, by doping a red phosphorescent dye Ir(MDQ)₂ (MDQ=2-methyldibenzo[f,h]quinoxaline) into the IP-PPI and IP-DPPI hosts, high-performance red phosphorescent OLEDs with EQEs of 20.8 % and 19.1 % were achieved, respectively. This work may provide a new approach for designing highly efficient deep-blue emitters with negligible roll-off for OLED applications.

Selective photoredox decarboxylation of α-ketoacids to allylic ketones and 1,4-dicarbonyl compounds dependent on cobaloxime catalysis

The selective synthesis of allylic ketones and 1,4-dicarbonyl compounds by photoredox/cobaloxime co-catalysis and photoredox catalysis, respectively, is described herein.

Intrinsically Cancer-Mitochondria-Targeted Thermally Activated Delayed Fluorescence Nanoparticles for Two-Photon-Activated Fluorescence Imaging and Photodynamic Therapy

A recent breakthrough in the discovery of thermally activated delayed fluorescence (TADF) emitters characterized by small single-triplet energy offsets (ΔE_ST) offers a wealth of new opportunities to exploit high-performance metal-free photosensitizers. In this report, two intrinsically cancer-mitochondria-targeted TADF emitters-based nanoparticles (TADF NPs) have been developed for two-photon-activated photodynamic therapy (PDT) and fluorescence imaging. The as-prepared TADF NPs integrate the merits of (1) high ¹O₂ quantum yield of 52%, (2) sufficient near-infrared light penetration depth due to two-photon activation, and (3) excellent structure-inherent mitochondria-targeting capabilities without extra chemical or physical modifications, inducing remarkable endogenous mitochondria-specific reactive oxygen species production and excellent cancer-cell-killing ability at an ultralow light irradiance. We believe that the development of such intrinsically multifunctional TADF NPs stemming from a single molecule will provide new insights into exploration of novel PDT agents with strong photosensitizing ability for various biomedical applications.

Bipolar Blue Host Emitter with Unity Quantum Yield Allows Full Exciton Radiation in Single-Emissive-Layer Hybrid White Organic Light-Emitting Diodes

Phosphorescence/fluorescence hybrid white organic light-emitting diodes (OLEDs) are highly appealing for solid-state lighting. One major challenge is how to fully utilize the electrically generated excitons for light output. Herein, an efficient strategy to realize full exciton radiation is successfully revealed by a judicious molecular design and suitable device engineering. A blue host emitter TP-PPI is designed and synthesized, exhibiting a near 100% photoluminescence quantum yield and a high triplet energy level, enabling high-performance blue fluorescence and sensitization of a yellow phosphorescent dopant. Full exciton radiation in hybrid white OLEDs is demonstrated with a single emitting layer formed by doping a yellow phosphor (PO-01) into TP-PPI. Near 100% exciton utilization and state-of-the-art external quantum efficiency of 27.5% are achieved with the high-efficiency blue-emitting host and an electron-trap engineered device architecture.

Photoinduced synthesis of fluorinated dibenz[b,e]azepines via radical triggered cyclization

A simple, mild and efficient approach to access fluorinated dibenz[b,e]azepines via visible-light photoredox catalysis is presented.

Novel phenanthroimidazole-based blue AIEgens: reversible mechanochromism, bipolar transporting properties, and electroluminescence

Multifunctional materials are crucial and have promising applications in a wide range of organic electronics.

Aromatically C6- and C9-Substituted Phenanthro[9,10-d]imidazole Blue Fluorophores: Structure-Property Relationship and Electroluminescent Application

In this study, a series of aromatically substituted phenanthro[9,10-d]imidazole (PI) fluorophores at C6 and C9 (no. 6 and 9 carbon atoms) have been synthesized and systematically characterized by theoretical, thermal, photophysical, electrochemical, and electroluminescent (EL) studies. C6 and C9 modifications have positive influences on the thermal properties of the new materials. Theoretical calculations suggest that the C6 and the C9 positions of PI are electronically different. Theoretical and experimental evidences of intramolecular charge transfer (ICT) between two identical moieties attaching to the C6 and the C9 positions are observed. Photophysical properties of the fluorophores are greatly influenced by size and conjugation extent of the substituents as well as linking steric hindrance. It is found that the C6 and C9 positions afford moderate conjugated extension compared to the C2 modification. Moreover, ICT characteristics of the new fluorophores increase as the size of the substituted aromatic group, and are partially influenced by steric hindrance, with the anthracene and the pyrene derivatives having the strongest ICT excited properties. EL performances of the fluorophores were evaluated as host emitters or dopants in organic light-emitting devices (OLEDs). Most of the devices showed significantly improved efficiencies compared to the OLED using the nonmodified emitter. Among all the devices, a 5 wt % TPI-Py doped device exhibited excellent performances with an external quantum efficiency >5% at 1000 cd/m² and a deep-blue color index of (0.155, 0.065), which are comparable to the most advanced deep-blue devices. Our study can give useful information for designing C6/C9-modificated PI fluorophores and provide an efficient approach for constructing high-performance deep-blue OLEDs.

Achieving efficient violet-blue electroluminescence with CIE y <0.06 and EQE >6% from naphthyl-linked phenanthroimidazole-carbazole hybrid fluorophores

Naphthyl-linked donor–π–acceptor fluorophores were utilized to achieve high performance and good color purity violet-blue emission in organic light-emitting devices (OLEDs).

In this work, we revealed a new approach for the development of efficient violet-blue emitting materials featuring a hybrid local and charge transfer (HLCT) excited state through the incorporation of naphthyl group(s) as a weak n-type π spacer in a donor–π–acceptor (D–π–A) system. The resulting materials (TPINCz and TPIBNCz) show improved intramolecular charge transfer properties and highly efficient violet-blue fluorescence. It is demonstrated that the pattern of the π spacers has significant influence on the photophysical properties. The incorporation of a naphthyl/binaphthyl spacer between the donor and acceptor moieties can alleviate the common dilemma that enhancing device performance by increasing the charge transfer excited properties often leads to red-shifted emissions. A device using TPINCz as an emissive dopant shows a violet-blue emission with CIE coordinates of (0.153, 0.059) and a record high EQE of 6.56 ± 0.11% at a brightness of 1000 cd m^–2. To the best of our knowledge, this performance is the highest among the reported devices with CIE_y ≤0.08. Our study provides a new pathway for the design of high-performance violet-blue emitters with a D–π–A architecture in organic electroluminescence applications.

High-Performance Blue OLEDs Based on Phenanthroimidazole Emitters via Substitutions at the C6- and C9-Positions for Improving Exciton Utilization

Donor-acceptor (D-A) molecular architecture has been shown to be an effective strategy for obtaining high-performance electroluminescent materials. In this work, two D-A molecules, Ph-BPA-BPI and Py-BPA-BPI, have been synthesized by attaching highly fluorescent phenanthrene or pyrene groups to the C6- and C9-positions of a locally excited-state emitting phenylamine-phenanthroimidazole moiety. Equipped with good physical and hybridized local and charge-transfer properties, both molecules show high performances as blue emitters in nondoped organic light-emitting devices (OLEDs). An OLED using Ph-BPA-BPI as the emitting layer exhibits deep-blue emission with CIE coordinates of (0.15, 0.08), and a maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 4.56 %, 3.60 cd A(-1) , and 3.66 lm W(-1) , respectively. On the other hand, a Py-BPA-BPI-based, sky-blue OLED delivers the best results among nondoped OLEDs with CIEy values of < 0.3 reported so far, for which a very low turn-on voltage of 2.15 V, CIE coordinates of (0.17, 0.29), and maximum CE, PE, and EQE values of 10.9 cd A(-1) , 10.5 lm W(-1) , and 5.64 %, were achieved, respectively. More importantly, both devices show little or even no efficiency roll-off and high singlet exciton-utilizing efficiencies of 36.2 % for Ph-BPA-BPI and 39.2 % for Py-BPA-BPI.

Carbon dots–quinoline derivative nanocomposite: facile synthesis and application as a “turn-off” fluorescent chemosensor for detection of Cu2+ ions in tap water

In this paper, a novel quinoline derivative: 8-(pyridin-2-ylmethoxy)quinoline-2-carboxylic acid (Q) has been successfully synthesized, then it was coupled with carbon dots (CDs) to synthesize a CDs–Q nanocomposite by a simple and green method.

Phenanthroimidazole derivatives as emitters for non-doped deep-blue organic light emitting devices

We synthesized eight phenanthroimidazole derivatives as blue emitters for OLED application and investigated the relationship between the molecule structure and optoelectronic properties.

A meta-molecular tailoring strategy towards an efficient violet-blue organic electroluminescent material

In this study, a novel violet-blue emitter m-BBTPI was designed and synthesized via meta-molecular tailoring. Using m-BBTPI as non-doped emitter, we obtained a high-efficiency violet-blue organic electroluminescent device.

An ESIPT fluorescent dye based on HBI with high quantum yield and large Stokes shift for selective detection of Cys

DPIN shows prominent ESIPT emission even in protic/polar solvents, and is further employed as a sensor for selective detection of Cys.

A highly selective and sensitive luminescent chemosensor for Zn2+ ions based on cyclometalated platinum(II) complexes

A novel luminescent Zn(2+) ions chemosensor, a cyclometalated platinum(II) bipyridyl acetylide complex, was designed. Of particular significance is that it shows a high sensitivity towards Zn(2+) ions without interference from other biologically important cations in acetonitrile. The tautomerization of amide favors detecting Zn(2+) ions among other HTM (heavy and transition metal) ions in aqueous systems.