Near-infrared Organic Light-emitting Diodes Research Articles

Fast Transfer of Triplet to Doublet Excitons from Organometallic Host to Organic Radical Semiconductors.

Spin triplet exciton formation sets limits on technologies using organic semiconductors that are confined to singlet-triplet photophysics. In contrast, excitations in the spin doublet manifold in organic radical semiconductors can show efficient luminescence. Here the dynamics of the spin allowed process of intermolecular energy transfer from triplet to doublet excitons are explored. A carbene-metal-amide (CMA-CF3) is employed as a model triplet donor host, since following photoexcitation it undergoes extremely fast intersystem crossing to generate a population of triplet excitons within 4ps. This enables a foundational study for tracking energy transfer from triplets to a model radical semiconductor, TTM-3PCz. Over 74% of all radical luminescence originates from the triplet channel in this system under photoexcitation. It is found that intermolecular triplet-to-doublet energy transfer can occur directly and rapidly, with 12% of triplet excitons transferring already on sub-ns timescales. This enhanced triplet harvesting mechanism is utilized in efficient near-infrared organic light-emitting diodes, which can be extended to other opto-electronic and -spintronic technologies by radical-based spin control in molecular semiconductors.

Introducing Internal Host Component to Thermally Activated Delayed Fluorescence Emitter for Efficient NIR Nondoped Organic Light-Emitting Diodes.

Developing thermally activated delayed fluorescence (TADF) near-infrared (NIR) organic light-emitting diodes (OLEDs) based on nondoped emitting layers is intriguing yet challenging, limited by low exciton utilization and notorious concentration quenching. Herein, a facile strategy is proposed to address this issue by incorporating an internal host component onto a traditional donor (D)-acceptor (A)-type red TADF molecule. A proof-of-concept emitter with an internal host is accordingly developed as well as a control one without an internal host. In the case of their monomer states, both emitters exhibit similar emission spectra due to their identical D-A pairs. However, under nondoped conditions, significant improvement in exciton utilization and quenching-resistant features are observed for the molecule with the internal host. The corresponding nondoped OLED yielded a maximum external quantum efficiency of 2.4%, with NIR emission peaking at 765 nm, which was a nearly 10-fold improvement relative to the efficiency based on the control molecule without an internal host. To the best of our knowledge, this result is on par with those of state-of-the art nondoped NIR TADF OLEDs in a similar emission region. These results offer a feasible pathway for the design and development of high-efficiency NIR nondoped OLEDs.

Wearable and Wavelength-Tunable Near-Infrared Organic Light-Emitting Diodes for Biomedical Applications.

Near-infrared organic light-emitting diodes (NIR OLEDs) have significant potential for wearable phototherapeutic applications because of the unique properties of the OLEDs, including their free-form electronics and the excellent biomedical effects of NIR emission. In spite of their tremendous promise, given that the majority of NIR OLEDs in previous research have relied on the utilization of an intrinsically brittle indium tin oxide (ITO) electrode, their practicality in the field of wearable electronics is inherently constrained. Here, we report wearable and wavelength-tunable NIR OLEDs that employ a high-performance NIR emitter and an innovative architecture by replacing the ITO with a silver (Ag) electrode. The NIR OLEDs permit wavelength tuning of emissions from 700 to 800 nm and afford stable operation even under repeated bending conditions. The NIR OLEDs provide a lowered device temperature of 37.5 °C even during continuous operation under several emission intensities. In vitro experiments were performed with freshly fabricated NIR OLEDs. The outcomes were evaluated against experimental results performed using the same procedure utilizing blue, green, and red OLEDs. When exposed to NIR light irradiation, the promoting effect of cell proliferation surpassed the proliferative responses observed under the influence of visible light irradiation. The proliferation effect of human hair follicle dermal papilla cells is clearly related to the irradiation wavelength and time, thus underscoring the potential of wavelength-tunable NIR OLEDs for efficacious phototherapy. This work will open novel avenues for wearable NIR OLEDs in the field of biomedical application.

Narrowband Pure Near-Infrared (NIR) Ir(III) Complexes for Solution-Processed Organic Light-Emitting Diode (OLED) with External Quantum Efficiency Over 16 .

Highly efficient near-infrared (NIR) emitters have significant applications in medical and optoelectronic fields, but the development stays a great challenge due to the energy gap law. Here, we report two NIR phosphorescent Ir(III) complexes which display emission peaks around 730 nm with a narrow full width at half maximum of only 43 nm. Therefore, pure NIR luminescence can be obtained without having a very long emission wavelength, thus alleviating the restriction of the energy gap law, and obtaining impressively high photoluminescence quantum yield up to 0.70. More importantly, the pure NIR organic light-emitting diode (OLED) fabricated by the solution-processed mothed shows outstanding device performance with the highest external quantum efficiency of 16.43 %, which sets a new record for solution-processed NIR-OLEDs based on different emitters. This work sheds light on the development of Ir(III) complexes with narrowband emissions as highly efficient pure NIR-emitters.

A Feasible Strategy for a Highly Efficient Thermally Activated Delayed Fluorescence Emitter Over 900 nm Based on Phenalenone Derivatives.

Near-infrared (NIR) organic light-emitting diodes (OLEDs) suffer from the low external electroluminescence (EL) quantum efficiency (EQE), which is a critical obstacle for potential applications. Herein, 1-oxo-1-phenalene-2,3-dicarbonitrile (OPDC) is employed as an electron-withdrawing aromatic ring, and by incorporating with triphenylamine (TPA) and biphenylphenylamine (BBPA) donors, two novel NIR emitters with thermally activated delayed fluorescence (TADF) characteristics, namely OPDC-DTPA and OPDC-DBBPA, are first developed and compared in parallel. Intense NIR emission peaks at 962 and 1003 nm are observed in their pure films, respectively. Contributed by the local excited (LE) characteristics in the triplet (T1 ) state in synergy with the charge transfer (CT) characteristics for the singlet (S1 ) state to activate TADF emission, the solution processable doped NIR OLEDs based on OPDC-DTPA and OPDC-DBBPA yield EL peaks at 834 and 906 nm, accompanied with maximum EQEs of 0.457 and 0.103 %, respectively, representing the state-of-the-art EL performances in the TADF emitter-based NIR-OLEDs in the similar EL emission regions so far. This work manifests a simple and effective strategy for the development of NIR TADF emitters with long wavelength and efficiency synchronously.

Heteroleptic Ir(III)-based near-infrared organic light-emitting diodes with high radiance capacity

Near-infrared organic light-emitting diodes (NIR OLEDs) with heavy metals are regularly reported due to the advantages of their various applications in healthcare services, veil authentication, and night vision displays. For commercial applications, it is necessary to look at radiance capacity (RC) instead of radiance because of power consumption. However, recent papers still reported only simple high radiance performance and do not look at device from the point of view of RC. To overcome this hurdle, we designed Ir(III)-based heteroleptic NIR materials with two types of auxiliary ligand. The proposed emitters achieve a highly oriented horizontal dipole ratio (Ir(mCPDTiq)2tmd, complex 1: 80%, Ir(mCPDTiq)2acac, complex 2: 81%) with a short radiative lifetime (1: 386 ns, 2: 323 ns). The device also shows an extremely low turn-on voltage (Von) of 2.2 V and a high RC of 720 mW/sr/m2/V. The results on the Von and RC of the device is demonstrated an outstanding performance among the Ir(III)-based NIR OLEDs with a similar emission peak.

Efficient radical-based near-infrared organic light-emitting diodes with an emission peak exceeding 800 nm

An OLED employing the TTM-NPNA radical as the emitter exhibits a high external quantum efficiency (EQE) value of 3.9% with an electroluminescence peak at 822 nm.

High-efficiency and stable red to near-infrared organic light-emitting diodes using dinuclear platinum(ii) complexes

High-performance red and NIR organic light-emitting diodes (OLEDs) have been achieved using highly robust and phosphorescent diplatinum(ii) complexes featuring strong intramolecular Pt–Pt and π–π interactions.

4,4′-([1,2,5]Thiadiazolo[3,4-d]pyridazine-4,7-diyl)bis(N,N-bis(4-methoxyphenyl)aniline)

Donor-acceptor-dyes with extended conjugation, such as D–π–A–π–D type, are being intensively investigated as components of near-infrared (NIR) organic light-emitting diodes (OLEDs). In this communication, novel D–π–A–π–D dye, 4,4′-([1,2,5]thiadiazolo[3,4-d]pyridazine-4,7-diyl)bis(N,N-bis(4-methoxyphenyl)aniline), was synthesized by Stille cross-coupling reaction of 4,7-dibromo-[1,2,5]thiadiazolo[3,4-d]pyridazine. The structure of newly synthesized compounds was established by elemental analysis, high-resolution mass-spectrometry, 1H, 13C NMR, IR, and UV spectroscopy. The photophysical properties of the title compound were studied.

A platform for blue-luminescent carbon-centered radicals

Organic radicals, which have unique doublet spin-configuration, provide an alternative method to overcome the efficiency limitation of organic light-emitting diodes (OLEDs) based on conventional fluorescent organic molecules. Further, they have made great breakthroughs in deep-red and near-infrared OLEDs. However, it is difficult to extend their fluorescence into a short-wavelength region because of the natural narrow bandgap of the organic radicals. Herein, we significantly expand the scope of luminescent radicals by showing a new platform of carbon-centered radicals derived from N-heterocyclic carbenes that produce blue to green emissions (444–529 nm). Time-dependent density functional theory calculations and experimental investigations disclose that the fluorescence originates from the high-energy excited states to the ground state, demonstrating an anti-Kasha behavior. The present work provides an efficient and modular approach toward a library of carbon-centered radicals that feature anti-Kasha’s rule emission, rendering them as potential new emitters in the short-wavelength region.

New pyridylimidazole-based near-infrared iridophosphors: Synthesis, photophysical properties, and electroluminescence application

A pair of highly efficient near-infrared (NIR) phosphorescent iridium(III) complexes (NIR-Ir1 and NIR-Ir2) based on pyridylimidazole derivatives are rationally designed. 1-(Benzo [b]thiophen-2-yl)isoquinoline is selected as the cyclomedtalating ligand for complexes, which determines the near-infrared phosphorescence. 2-(1H-imidazole-2-yl)pyridine and 2-(pyridin-2-yl)-1H-benzo[d]imidazole serve as the ancillary ligands, which aims to finely adjust the photophysical properties of these two NIR iridophosphors. At room temperature, both complexes exhibit intense near-infrared phosphorescence and the emission spectra well overlap with each other (685 nm with 750 nm as the emission shoulder for NIR-Ir1 and NIR-Ir2), high photoluminescence quantum yield (0.10 for NIR-Ir1, 0.13 for NIR-Ir2) in dichloromethane. The pyridylimidazole-type ancillary ligands incorporated into the complexes enable the effective NIR phosphorescence and the robust chemical stability for NIR organic light-emitting diodes (OLEDs). The preliminary results show that the maximum luminescence and external quantum efficiency for the OLEDs based on new NIR complexes with electroluminescence peaked at around 690 nm are 1,464 cd/m2 and 1.48%, respectively.

Cell proliferation effect of deep-penetrating microcavity tandem NIR OLEDs with therapeutic trend analysis

Long wavelengths that can deeply penetrate into human skin are required to maximize therapeutic effects. Hence, various studies on near-infrared organic light-emitting diodes (NIR OLEDs) have been conducted, and they have been applied in numerous fields. This paper presents a microcavity tandem NIR OLED with narrow full-width half-maximum (FWHM) (34 nm), high radiant emittance (> 5 mW/cm2) and external quantum efficiency (EQE) (19.17%). Only a few papers have reported on biomedical applications using the entire wavelength range of the visible and NIR regions. In particular, no biomedical application studies have been reported in the full wavelength region using OLEDs. Therefore, it is worth researching the therapeutic effects of using OLED, a next-generation light source, and analyzing trends for cell proliferation effects. Cell proliferation effects were observed in certain wavelength regions when B, G, R, and NIR OLEDs were used to irradiate human fibroblasts. The results of an in-vitro experiment indicated that the overall tendency of wavelengths is similar to that of the cytochrome c oxidase absorption spectrum of human fibroblasts. This is the first paper to report trends in the cell proliferation effects in all wavelength regions using OLEDs.

Tetracoordinate Boron-Based Multifunctional Chiral Thermally Activated Delayed Fluorescence Emitters.

Purely organic emitters have shown great potential but still suffer from low efficiency in near-infrared organic light-emitting diodes (NIR-OLEDs) due to the intensive non-radiative recombination. In this contribution, two pairs of thermally activated delayed fluorescence (TADF) enantiomers (R/S-DOBP and R/S-HDOBP) with tetracoordinate boron geometries were designed and synthesized. The TADF emitters simultaneously showed aggregation-induced emission, circularly polarized luminescence, high-contrast mechanochromism, and piezochromism behaviors. More importantly, R/S-DOBP and R/S-HDOBP revealed high photoluminescence quantum yields and efficient reverse intersystem crossing in neat films. The nondoped solution-processed OLEDs based on these unique emitters revealed the NIR emission (peaking at 716 nm) with a maximum external quantum efficiency of 1.9 % and high exciton utilization efficiency of 86 %, which represent one of the best solution-processed nondoped NIR-OLEDs.

Tetracoordinate Boron‐Based Multifunctional Chiral Thermally Activated Delayed Fluorescence Emitters

AbstractPurely organic emitters have shown great potential but still suffer from low efficiency in near‐infrared organic light‐emitting diodes (NIR‐OLEDs) due to the intensive non‐radiative recombination. In this contribution, two pairs of thermally activated delayed fluorescence (TADF) enantiomers (R/S‐DOBP and R/S‐HDOBP) with tetracoordinate boron geometries were designed and synthesized. The TADF emitters simultaneously showed aggregation‐induced emission, circularly polarized luminescence, high‐contrast mechanochromism, and piezochromism behaviors. More importantly, R/S‐DOBP and R/S‐HDOBP revealed high photoluminescence quantum yields and efficient reverse intersystem crossing in neat films. The nondoped solution‐processed OLEDs based on these unique emitters revealed the NIR emission (peaking at 716 nm) with a maximum external quantum efficiency of 1.9 % and high exciton utilization efficiency of 86 %, which represent one of the best solution‐processed nondoped NIR‐OLEDs.

Tetradentate cyclometalated platinum complex enables high-performance near-infrared electroluminescence with excellent device stability

Due to the high decay rate of the non-radiative transition of long wavelengths, the molecular design of efficient and stable near-infrared (NIR) electroluminescent materials remains a big challenge. Herein, a new tetradentate cyclometalated platinum(II) complex with an N∧C∧C∧N coordinated framework has been developed and used as a dopant for NIR organic light-emitting diodes (OLEDs). The complex exhibited a short-lived (0.5–1.5 µs) metal-to-ligand charge transfer (MLCT) excited state in doped and neat films. The resulting NIR OLEDs (λEL = 730 nm) achieved maximum external quantum efficiency (EQEmax) of 5.2% and radiance of 74626 mW sr−1 m–2. Of note, the device exhibited excellent stability with operational lifetime of 119 h for LT90. This work demonstrated the great potential of tetradentate platinum(II) complexes in the field of NIR OLEDs.

Rational Strategy for Constructing Efficient Hybrid Local and Charge Transfer-Type Deep Red to Near-Infrared Organic Light-Emitting Diodes

Rational Strategy for Constructing Efficient Hybrid Local and Charge Transfer-Type Deep Red to Near-Infrared Organic Light-Emitting Diodes

Efficient pure near-infrared organic light-emitting diodes based on tris(2,4,6-trichlorophenyl)methyl radical derivatives

An OLED based on TTM-3PDMAC achieved a maximum external quantum efficiency (EQE) of 3.1% with an emission peak at 830 nm.

Extremely low efficiency roll-off in vacuum- and solution-processed deep-red/near-infrared OLEDs based on 1,8-naphthalimide TADF emitters

Deep-red to near-infrared (DR-NIR) organic light-emitting diodes (OLEDs) based on purely organic thermally activated delayed fluorescence (TADF) emitters usually suffer from serious efficiency roll-offs. Herein, a series of 1,8-Naphthalimide-derivatives-based wedge-shape emitters, 2DN and 2PN, were designed and synthesized by adopting multiple donor units and isopropyl modification strategies. 2DN and 2PN exhibited strong DR-NIR TADF in the range 646–755 nm in toluene and films. The OLEDs, fabricated by both vacuum-deposition and solution-processed methods, all exhibited desired DR-NIR electroluminescence in the range 629–701 nm, and significantly reduced efficiency roll-offs (8.4% for 2DN and near zero for 2PN at 100 cd m−2), which benefit from short delayed lifetime (36.4 us for 2DN and 14.0 us for 2PN) and negligible π-π stacking in aggregation states. It indicates that the efficiency roll-offs of DR-NIR TADF OLEDs can be greatly reduced by designing emitters with appropriate design of molecular structures.

Stable and Efficient Near-Infrared Organic Light-Emitting Diodes Employing a Platinum(II) Porphyrin Complex.

Stable and efficient emitters are highly desired for near-infrared organic light-emitting diodes (NIR OLEDs) due to their extensive applications in biometric authentication, night vision display, and telecommunication. As this technology advances, there is an increasing demand for the development of NIR OLEDs with an emission spectrum beyond 900 nm. This work reports a stable and efficient near-infrared Pt(II) porphyrin complex, i.e., Pt(II) tetra(3,5-difluorophenyl)tetranaphthoporphyrin named PtTPTNP-F8, of which 84% of the total emitted photons are at wavelengths longer than 900 nm. By introducing fluorine atoms on the meta positions of all four phenyl groups, PtTPTNP-F8 can successfully overcome the common thermal instability issue emerging from the heavy Pt(II) porphyrin complexes, demonstrating a sublimation yield of above 90%. By carefully choosing the host materials, a NIR OLED device with PtTPTNP-F8 as an emissive material achieves a high peak device efficiency of 1.9%. Furthermore, devices of PtTPTNP-F8 fabricated in a stable device structure demonstrate extraordinary operational stability with an LT99 lifetime (time to 99% of the initial photocurrent) of more than 1000 h at a constant driving current density of 20 mA cm-2.

Near-infrared organic light-emitting diodes of pure fluorescence emission using small-molecule boron-dipyrromethene derivative

Near-infrared (NIR) light has various applications, such as in cameras and sensors. Organic light-emitting diodes (OLEDs), which are characterized by their thinness, lightweight, and flexibility, have potential application in various devices requiring light emission in the NIR region. In this study, we focused on the wavelength range of 700–1000 nm, which is called the “first optical window” in NIR light. Furthermore, we investigated the optical properties of a low-molecular-weight boron-dipyrromethene derivative (BODIPY-Ph), which has been reported to possess NIR absorption properties as well as the luminescence properties of BODIPY-Ph-based OLEDs in the NIR region. An acetone solution of BODIPY-Ph showed 52.3% photoluminescence quantum yield and the apparent external quantum efficiency of the OLED in the NIR region was high at 1.87%, which is one of the highest values when using OLEDs that are metal-free and use pure fluorescence emission without using triplet.