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

A High-Efficiency Ultraviolet Organic Light-Emitting Diode Employing a Double Boron-Oxygen-Nitrogen-Based Emitter

Designing high-efficiency ultraviolet organic light-emitting diodes (UV OLEDs) remains challenging due to the need for efficient utilization of triplet excitons while maintaining a wide bandgap. In this study, we designed double boron-oxygen-nitrogen-based polycyclic aromatic hydrocarbons (dBON-PAHs) with rigid planar structures and developed a novel UV emitter, BO-N, featuring hybridized local and charge-transfer (HLCT) properties. BO-N exhibited UV emission in toluene solution and 1,3-di(9H-carbazol-9-yl)benzene (mCP) film, with photoluminescence (PL) peaks of 391 and 400 nm and narrow full width at half-maximum (FWHM) values of 15 and 34 nm, respectively. The device doped with 5 wt% BO-N achieved a narrowband UV emission with an FWHM of 37 nm, an electroluminescence peak (λEL) of 399 nm, and CIE coordinates of (0.166, 0.030). Moreover, the device attained a record-high maximum external quantum efficiency (EQEmax) of 18.6% among reported HLCT-based UV OLEDs with CIEy < 0.05. These findings highlight the great potential of double BON-PAHs as robust emitters for high-performance UV OLEDs.

A through-space charge transfer pyrene-based fluorophore with anti-quenching behavior for deep-blue organic light-emitting devices

A through-space charge transfer pyrene-based fluorophore has been developed for organic light-emitting devices (OLEDs). This material exhibits deep-blue fluorescence, bipolar characteristics, and anti-quenching behavior in the solid state. It proves to be an effective emitter for both doped and nondoped deep-blue OLEDs.

Toward Narrowband and Efficient Blue Fluophosphors by Locking the Stretching Vibration of Indolocarbazole Skeletons

Developing efficient and color-saturated deep-blue emitting molecules with small Commission Internationale de L'Eclairage (CIE) y values is challenging and has great potential for wide-color gamut displays. Herein, we introduce an intramolecular locking strategy to restrain molecular stretching vibrations of the emission spectral broadening. By cyclizing rigid fluorenes and connecting electron-donating groups to the indolo[3,2,1-jk]-indolo[1',2',3':1,7]indolo[2,3-b]carbazole (DIDCz) framework, the in-plane swing of peripheral bonds and stretching vibrations of the indolocarbazole skeleton are restricted due to an increased steric hindrance from cyclized groups and diphenylamine auxochromophores. As a result, reorganization energies at the high-frequency region (1300-1800 cm-1) are reduced, realizing pure blue emission with a small full-width-at-half-maximum (FWHM) of 30 nm by suppressing shoulder peaks of polycyclic aromatic hydrocarbon (PAH) frameworks. The fabricated bottom-emitting organic light-emitting diode (OLED) exhibits an efficient external quantum efficiency (EQE) of 7.34% and deep-blue coordinates of (0.140, 0.105) at a high brightness of 1000 cd/m2. The FWHM of the electroluminescent spectrum is only 32 nm, which is one of the narrowest electroluminescent emissions among the reported intramolecular charge transfer fluophosphors. Our current findings provide a new molecular design strategy to conceive efficient and narrowband emitters with small reorganization energies.

Indolo[3,2,1-jk]carbazole-Derived Narrowband Violet-Blue Fluorophores: Tuning the Optical and Electroluminescence Properties by Chromophore Juggling

The development of rigid polyaromatic building blocks for narrowband violet fluorophores has received tremendous attention. Herein, we designed and synthesized two new triangle-shaped rigid building blocks, namely, 2,5-di-tert-butylindolo[3,2,1-jk]carbazole (tBuICz) and 2,11-di-tert-butylindolo[3,2,1-jk]carbazole-4-carbonitrile (tBuICzCN), and tethered them with different chromophores to yield a series of violet-blue fluorophores, viz., ICzTPA-ICzPICN, and studied their structure-function relationship. The appended chromophores and cyano unit played a vital role in controlling the optical and electrical properties of the compounds. Except triphenylamine-substituted derivatives, the compounds showed pure violet emission (λ_em ≤ 403 nm). Intriguingly, the compounds exhibited narrow-band emission with a full-width at half-maximum ≤ 40 nm, attributed to the rigidity of the ICz core. The emission of the compounds displayed positive solvatochromism, which is ascribed to the photoinduced intramolecular charge transfer in the excited state. The compounds revealed excellent thermal robustness with T_5d ≥ 363 °C. The triphenylamine-featuring derivatives displayed a high-lying HOMO compared to their congeners due to their electron-rich nature. When we applied these materials in organic light-emitting diodes, ICzPI outperformed in the series with an EQE_max of 3.07% and a current efficiency of 1.04 cd/A. Notably, its CIEy ∼ 0.046 precisely matched with the Rec.2020 standard of deep-blue color (CIEy ∼ 0.046).

Exploration of novel TOSMIC tethered imidazo[1,2-a]pyridine compounds for the development of potential antifungal drug candidate

New candidates of imidazo[1,2-a]pyridine were designed by combining 2-amino pyridine, TOSMIC and various assorted aldehydes to explore their antioxidant and antifungal potential. The design of these derivatives was based on utilizing the antifungal potential of azoles and TOSMIC moiety. These derivatives were synthesized by adopting multi-component reaction methodology, as it serves as a rapid and efficient tool to target structurally diverse heterocyclic compounds in quantitative yield. The resulting imidazo[1,2-a]pyridine derivatives were structurally verified by ¹ HNMR, ¹³ CNMR, HRMS, and HPLC. The compounds were analyzed for their antioxidant and fluorescent properties and it was observed that compound 15 depicted highest potential. The compounds were evaluated for their antifungal potential to highlight their medical application in the area of Invasive Fungal Infections (IFI). Compound 12 gave the highest antifungal inhibition against Aspergillus fumigatus 3007 and Candida albicans 3018. To elucidate the antifungal mechanism, confocal images of treated fungi were analyzed, which depicted porous nature of fungal membrane. Estimation of fungal membrane sterols by UPLC indicated decrease in ergosterol component of fungal membrane. In silico studies further corroborated with the in vitro results as docking studies depicted interaction of synthesized heterocyclic compounds with amino acids present in the active site of target enzyme (lanosterol 14 alpha demethylase). Absorption, distribution, metabolism, and excretion (ADME) analysis was indicative of drug-likeliness of the synthesized compounds.

Dicyano-Imidazole: A Facile Generation of Pure Blue TADF Materials for OLEDs

A series of dicyano-imidazole-based molecules with thermally activated delayed fluorescence (TADF) properties were synthesized to obtain pure blue-emitting organic light-emitting diodes (OLEDs). The targeted molecules used dicyano-imidazole with a short-conjugated system as the electron acceptor to strong intermolecular π-π interactions, and provide a relatively shallow energy level of the lowest unoccupied molecular orbital (LUMO). The cyano group was selected to improve imidazole as an electron acceptor due to its prominent electron-transporting characteristics. Four different electron donors, that is, 9,9-dimethyl-9,10-dihydroacridine (DMAC), 10H-spiro(acridine-9,9'-fluoren) (SPAC), and 9,9-diphenyl-9,10-dihydroacridine (DPAC), were used to alternate the highest occupied molecular orbital (HOMO) energy level to tune the emission color further. The crowded molecular structure in space makes the electron donor and acceptor almost orthogonal, reducing the energy gap (ΔE_ST ) between the first excited singlet (S₁ ) and the triplet (T₁ ) states and introducing significant TADF property. The efficiencies of the blue-emissive devices with imM-SPAC and imM-DMAC obtained in this work are the highest among the reported imidazole-based TADF-OLEDs, which are 13.8 % and 13.4 %, respectively. Both of Commission Internationale de l'Eclairage (CIE) coordinates are close to the saturated blue region at (0.17, 0.18) and (0.16, 0.19), respectively. Combining these tailor-made TADF compounds with specific device architectures, electroluminescent (EL) emission from sky-blue to deep-blue could be achieved, proving their great potential in EL applications.

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.

Violet-Blue Emitters Featuring Aggregation-Enhanced Emission Characteristics for Nondoped OLEDs with CIEy Smaller than 0.046

High emission efficiency and finite molecular conjugation in the aggregate state are two desirable features in violet-blue emitters. Aggregation-induced emission luminogens (AIEgens) have emerged as promising luminescent materials that offer these features. Herein, we report the design and synthesis of a group of violet-blue tetraphenylbenzene-based AIEgens with photoluminescence quantum yields over 98% in their film states. When utilizing these AIEgens as nondoped emitting layers, the fabricated organic light-emitting diode exhibits a maximum external quantum efficiency of 4.34% with Commission Internationale de L'Eclairage (CIE) coordinates of (0.159, 0.035), which is amenable to the next-generation ultrahigh-definition television (UHDTV) display standard.

Conformational analysis and quantum descriptors of two new imidazole derivatives by experimental, DFT, AIM, molecular docking studies and adsorption activity on graphene

1-[2-(2-hydroxy-3-methoxy-5-(4-methoxyphenylazo)benzaldeneamino)ethyl]-3-methyl-3H-imidazole (HMY) and 1-[2-(2-hydroxy-3-methoxy-5-(4-methylphenylazo)benzaldene amino)ethyl]-3-methyl-3H-imidazole (HMM) were synthesized and characterized using spectral analysis. Conformational analysis has been achieved using potential energy scan for different rotable bonds for obtaining the lowest energy conformer. Conformer with minimum energy is obtained along the dihedral angle N30-C31-C34-N37. QTAIM analysis gives nature and strength of hydrogen bonding interactions. UV-Vis, electrostatic potential and chemical descriptors are analyzed. Interaction of HMY and HMM with graphene is analyzed in terms of SERS activity. Chemical reactivity descriptors were investigated for graphene-drug systems. NLO activity of parent drugs and its graphene complexes show good activity. The wavenumber downshift of different modes is noted. Title molecules exhibit inhibitory activity against cytochrome C peroxidase. Interactions with graphene sheets are theoretically predicted for the title compounds.

Efficient blue electroluminescence with an external quantum efficiency of 9.20% and CIE y < 0.08 without excimer emission

Aromatically substituted phenanthroimidazoles at the C6 and C9 positions enhanced the thermal, photochemical and electroluminescence properties due to extension of conjugation. These new materials exhibit good photophysical properties with high thermal stability, good film-forming property and high luminous efficiency. The electroluminescence performances of C6 and C9 modified phenanthroimidazoles as host emitters were evaluated as well as the dopant in the fabricated devices. Among the non-doped devices, pyrene substituted PPI-Py or PPICN-Py based devices show maximum efficiency: PPI-Py/PPICN-Py: η c (cd A-1) - 9.20/9.98; η p (lm W-1) - 8.50/9.16; η ex (%) - 5.56/5.80. The doped OLEDs, m-MTDATA/TAPC:PPI-Cz (4.81/4.85%), m-MTDATA/TAPC:PPICN-Cz (5.23/5.26%), m-MTDATA/TAPC:PPI-An (5.01/5.04%), m-MTDATA/TAPC:PPICN-An (5.25/5.28%), m-MTDATA/TAPC:PPI-Py (5.61/5.65%) and m-MTDATA/TAPC:PPICN-Py (5.76/5.78%) show improved device efficiencies compared to non-doped devices. Designing C6/C9 modified phenanthrimidazole fluorophores is an efficient strategy for constructing highly efficient OLEDs.

Efficient fluorescent OLEDS based on assistant acceptor modulated HLCT emissive state for enhancing singlet exciton utilization

Phenylamine phenanthroimidazole based bipolar compounds with donor-acceptor (D-A) architecture namely, 4-(1-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-6,9-di(pyren-4-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenylaniline (DDPPPA) and 4'-(1-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-6,9-di(pyren-4-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1'-biphenyl]-4-amine (DDPBA) have been synthesized with highly fluorescent pyrene moieties at C6- and C9-positions. The C6 and C9 modification enhanced the thermal, photochemical and electroluminescent properties. Both molecules were employed as blue emitters in non doped organic light emitting devices (OLEDs) and show high performances due to hybridized local and charge-transfer properties. An OLED with DDPPPA/DDPBA emissive layer shows deep-blue emission with maximum external quantum efficiency (η ex), current efficiency (η c) and power efficiency (η p) of 5.7/6.0%, 10.5/12.0 cd A-1 and 8.3/9.2 lm W-1, respectively. Both devices show high singlet exciton utilizing efficiency (η s) of DDPPPA-31.33% and DDPBA-35.29%. The doped device m-MTDATA:DDPPPA/m-MTDATA:DDPBA shows maximum efficiencies of η c -7.4/8.23 cd A-1; η p -5.8/6.13 lm W-1; η ex -4.72/5.63% (5 wt%):η c -8.36/9.15 cd A-1; η p -6.32/6.65 lm W-1; η ex -4.86/5.45% (10 wt%):η c -9.58/10.02 cd A-1; η p -7.8/8.25 lm W-1; η ex -5.96/6.25% (20 wt%). The doped device based on TAPC host TAPC:DDPPPA/TAPC:DDPBA exhibits maximum efficiencies of η c -9.60/10.03 cd A-1; η p -7.81/8.26 lm W-1; η ex -5.96/6.25% (20 wt%).

Synthesis, photophysical, quantum chemical investigation, linear and non-linear optical properties of coumarin derivative: Optoelectronic and optical limiting application

In order to develop a new photostable, light emitting and highly efficient synthesized material to exhibit display property and non-linear optical active materials with good band gap energy, we have synthesized molecule via simple catalytic method. The photophysical property of studied molecule in various organic solvents having different polarity exhibited considerably acceptable results. The results of quantum yield, lifetime and large Stoke shift shows the compound is a good promising candidate for the laser dyes and light emitting diode color filters. The energy band gap was determined by both experimentally and theoretically which is found to be an average of 3.2 eV which is well matched to the semiconducting materials band gap. The non-linear optical absorption properties of the synthesized molecule are dissolved in suitable solvents had been investigated using Z-scan technique. We have determined the sign and magnitude of nonlinear absorption coefficient by the method of open aperture Z-scan setup using an Nd: YAG continuous wave laser at 532 nm. The open aperture Z-scan profiles clearly demonstrate the presence of reverse saturable absorption kind nonlinearity in the investigated compound and are due to the two-photon absorption. Results of the non-linear optical studies confirm that the studied compound is more latent applications for optical limiting in continuous wave regime. Further, the optoelectronic properties were investigated the international commission on illumination, color rendering index, color purity, and correlated color temperature is results of the studied molecule in all studied solvents revels that this compound exhibits blue to cyan color and is suitable for organic light emitting diode which can be preferably used for daylight applications.

Charge Transfer Platform and Catalytic Amplification of Phenanthroimidazole Derivative: A New Strategy for DNA Bases Recognition

Research about DNA composition has been concentrated on DNA damage in the past few decades. However, it still remains a great challenge to construct a rapid, facile, and accurate approach for simultaneously monitoring four DNA bases, guanine (G), adenine (A), thymine (T), and cytosine (C). Herein, a novel electrochemical sensor based on phenanthroimidazole derivative, 2-(4-bromophenyl)-1-phenyl-1H-phenanthro[9,10-d]-imidazole (PPI), is successfully fabricated by a simple electrochemical method. The bromophenyl group in PI could expand their aromatic plane, induce the π-conjugated extension, and enhance the charge transfer and π-π interaction. The phenyl group at N1 position could regulate the intermolecular interaction, which could promote the possibility of intermolecular connection. The PPI polymer (poly(PPI)) with π-electron enriched conjugation architecture has been applied in simultaneous determination of G, A, T, and C in neutral solution by square wave voltammetry (SWV) method with well-separated peak potentials at 0.714, 1.004, 1.177, and 1.353 V, respectively. The sensor functionalized with poly(PPI) exhibits wide linear response for G, A, T, and C in the concentration ranges of 3-300, 1-300, 30-800, and 20-750 μM, respectively. With favorable selectivity, stability, and reproducibility, the sensor is successfully utilized to monitor four DNA bases in real samples, displaying a promising prospect for electrochemical sensing devices.

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.

Efficient Deep-Blue Electrofluorescence with an External Quantum Efficiency Beyond 10

The design of blue fluorescent materials combining both deep-blue emission (CIE_y<0.06) and high-efficiency climbing over the typically limited exciton production efficiency of 25% is a challenge for organic light-emitting diodes (OLEDs). In this work, we have synthesized two blue luminogens, trans-9,10-bis(2-butoxyphenyl)anthracene (BBPA) and trans-9,10-bis (2,4-dimethoxyphenyl)anthracene with high photoluminescence quantum yields (PLQYs) of 89.5% and 87.0%, respectively. Intriguingly, we have proposed a strategy to avoid aggregation-caused quenching, which can effectively reduce the undesirable excimeric emission by introducing two host matrices with twisted molecular structure, 9,10-di(naphth-2-yl) anthracene and 10,10′-bis-(4-fluorophenyl)-3,3′-dimethyl-9,9′-bianthracene (MBAn-(4)-F), in the BBPA emission layer. The device containing the EML of BBPA-doped MBAn-(4)-F exhibited a high external quantum efficiency of 10.27% for deep-blue emission with the Commission International de L'Eclairage CIE coordinates of (0.15, 0.05) via the steric effect. Importantly, this represents an advance in deep-blue-emitting fluorescent OLED architectures and materials that meet the requirements of high-definition display.

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Highly efficient deep-blue luminogens BBPA and DMPA are synthesized

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Low-efficiency roll-off deep-blue OLEDs with CIE coordinate Y < 0.06

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Record-high external quantum efficiency of 10.27% for deep-blue fluorescent OLEDs

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Host matrix of twisted structure showing steric effect reduces intermolecular aggregation

Tuning the Photophysical and Electroluminescence Properties in Asymmetrically Tetrasubstituted Bipolar Carbazoles by Functional Group Disposition

Carbazoles decorated with both donor and acceptor fragments offer a classical way to optimize bipolar functional properties. In this work, a series of carbazoles featuring triphenylamine donors and cyano acceptors are synthesized and their structure-property relationship is studied. The effects of connectivity and the chromophore number density on photophysical and electroluminescence properties are investigated. The position of the triphenylamine donor on the 3,6-dicyanocarbazole nucleus significantly affected the photophysical and electroluminescence properties. The dye possessing triphenylamine on C2 and C7 displayed a red shift in absorption when compared with the structural analogue with triphenylamine tethered to C1 and C8. The emission wavelength of the dyes are tunable from blue to green, by altering the position of triphenylamine and cyano substituents. All of the dyes exhibited positive solvatochromism in emission, attributable to the photoinduced intramolecular charge transfer from the triphenylamine donor to the cyano acceptor. However, the extent of charge transfer and hybridization of local and charge-transfer-excited states is highly dependent on the position of triphenylamine and cyano groups on the carbazole nucleus. Dyes containing cyano substituents at C2 and C7 showed a prolonged excited state lifetime, broad emission, and large Stokes shifts, indicating the presence of a higher charge transfer component in the excited state. The dyes displayed exceptional thermal stability with the onset decomposition temperature (10% weight loss) > 350 °C. Electrochemical measurements revealed low oxidation potential for dyes containing triphenylamine at C3 and/or C6. Addition of a cyano acceptor on carbazole led to the stabilization of lowest unoccupied molecular orbital. Furthermore, the materials were tested as emitting dopants in solution-processable multilayer organic light emitting diodes and found to display deep-blue/sky-blue electroluminescence with external quantum efficiency as high as 6.5% for a deep-blue emitter (CIE y ∼ 0.06).