Sharp Spectra Research Articles

Bimolecular Sandwich Aggregates of Porphyrin Nanorings.

Extended π-systems often form supramolecular aggregates, drastically changing their optical and electronic properties. However, aggregation processes can be difficult to characterize or predict. Here, we show that butadiyne-linked 8- and 12-porphyrin nanorings form stable and well-defined bimolecular aggregates with remarkably sharp NMR spectra, despite their dynamic structures and high molecular weights (12.7 to 26.0 kDa). Pyridine breaks up the aggregates into their constituent rings, which are in slow exchange with the aggregates on the NMR time scale. All the aggregates have the same general two-layer sandwich structure, as deduced from NMR spectroscopy experiments, including 1H DOSY, 1H-1H COSY, TOCSY, NOESY, and 1H-13C HSQC. This structure was confirmed by analysis of residual dipolar couplings from 13C-coupled 1H-13C HSQC experiments on one of the 12-ring aggregates. Variable-temperature NMR spectroscopy revealed an internal ring-on-ring rotation process by which two π-π stacked conformers interconvert via a staggered conformation. A slower dynamic process, involving rotation of individual porphyrin units, was also detected by exchange spectroscopy in the 8-ring aggregates, implying partial disaggregation and reassociation. Molecular dynamics simulations indicate that the 8-ring aggregates are bowl-shaped and highly fluxional, compared to the 12-ring aggregates, which are cylindrical. This work demonstrates that large π-systems can form surprisingly well-defined aggregates and may inspire the design of other noncovalent assemblies.

Quantum Dots and Molecular Junctions as Energy Filters for Thermal-to-Electric Energy Conversion

The thermoelectric conversion of heat into electricity requires a form of energy filtering, that allows hot electrons to pass while blocking cold electrons. The energy conversion efficiency is determined by the details of the energy filtering, with an infinitely sharp (delta function) transmission spectrum allowing near ideal (Carnot) efficiency. [1]I will introduce this concept and report on a proof-of-performance experiment based on a quantum dot embedded into a single, semiconductor nanowire. This near-ideal quantum-dot heat engine realized power production at maximum power with Curzon-Ahlborn efficiency as well more than 70% of Carnot efficiency at maximum efficiency settings [2].To further enhance efficiency at maximum power one wishes to shape the transmission function to allow a spectrum of warmer electrons to pass while still completely blocking cold electrons. This may be achieved by exploiting quantum interference phenomena to block low-energy electron transmission by destructive interference, and to thus sculpt the transmission function of quantum dots or molecular junctions.[4] In contrast to quantum dots, molecular junctions have the advantage that they can be used at room temperature and can be produced, in principle, cheaply and scalable. To systematically explore the effect of quantum interferences, we designed and synthesized a new class of porphyrins that are expected to feature destructive quantum interference in single molecule junctions with gold electrodes and may thus show high thermopower, as well as a control that does not. We performed detailed experimental single-molecule break-junction studies of conductance and thermopower on porphyrin molecular junctions. We find a somewhat better thermoelectric performance for the porphyrin where we expect destructive interference. However, the predicted large difference in conductance and thermopower is not supported by our experimental findings.[4]Finally, I will also briefly discuss the potential application of the concepts and systems presented here in hot-carrier photovoltaics, as an approach to increasing photovoltaic energy conversion efficiency beyond current limits.[1] T.E. Humphrey et al., Reversible Quantum Brownian Heat Engines for Electrons. Phys. Rev. Lett., 89, 116801 (2002)[2] M. Josefsson et al. A quantum-dot heat engine operated close to thermodynamic efficiency limits. Nature Nanotechn. 13, 920 (2018)[3] O Karlström et al. Increasing thermoelectric performance using coherent transport. Phys. Rev. B 84, 113415 (2011)[4] H. Xu et al. Electrical Conductance and Thermopower of β-Substituted Porphyrin Molecular Junctions Synthesis and Transport. JACS 145 , 23541 (2023) Figure 1

LH launchers for tokamaks at IPR

Earlier, a conventional grill launcher-based LHCD system has been developed to drive plasma current non-inductively in tokamaks at IPR (ADITYA and SST1) at a frequency (fo = ωo/2π) of 3.7 GHz, which has the ability to launch pure spectrum with high directivity. Grill having large number of sub-waveguides launches a sharp spectrum, which drive LH current more efficiently and therefore was preferred for carrying out plasma physics studies in a controlled manner. An over-dense plasma near the mouth of the launcher provides good coupling of LHWs with plasma and therefore the grill launcher needs to be placed close to the last close flux surface (LCFS). The grill launcher at IPR allows to launch LHWs having a parallel refractive index (N||) from 1.5 to 4.0 by varying the phase difference between adjacent sub-waveguides from 60° to 160°. For ADITYA tokamak, owing to space constraints, the grill launcher with eight sub-waveguides (arranged in two rows, each having four sub-waveguides) could be developed to launch of power up to 120 kW, and therefore, the topology of the ADITYA LHCD was not very complex. However, for the 1 MW LHCD system for SST1 tokamak, the grill launcher with sixty-four sub-waveguides (arranged in two rows, each having thirty-two sub-waveguides) was developed and the SST1 LHCD system, thus conceived, was huge and very complex offering tremendous engineering design challenges. For reactor-grade plasmas, where rf power of a few tens of MW would be launched in to the plasmas, a more compact and reactor-relevant LH launcher, often known as passive–active multijunction (PAM) is foreseen. The PAM launcher offers very good coupling with low reflection co-efficient (∼2–5%) when the plasma density near the mouth of the launcher is near cutoff densities for a given frequency (ωo = ωpe, the electron plasma frequency), and thus allowing it to be placed far away from the LCFS of the plasma, thereby minimizing deleterious effects on launcher due to hostile edge plasma conditions and makes this launcher relevant for reactor-grade plasmas. Further, the space behind the passive waveguide can be utilized for neutron shielding and efficient thermal management. On the contrary, it offers reduced directivity and the spectrum can be varied over a narrow range. Further, the network of transmission lines feeding this launcher is relatively simpler and offers less technological challenges. Thus, 250-kW PAM launcher (comprising of two modules)-based LHCD system for ADITYA-U tokamak has been designed and developed. The launched N|| may be varied over a narrow range (2.25 ± 0.375) by varying the phase difference between adjacent modules over 180° ± 90°. The physics requirements, design philosophy, engineering challenges/solutions, the key outcome and achievements as we embark on to PAM launcher are presented and discussed. Based on our experience of PAM launcher, for ADITYA-U tokamak, conceptual design of the PAM launcher for SST1 is also presented.

Phytonano silver for cosmetic formulation- synthesis, characterization, and assessment of antimicrobial and antityrosinase potential.

Novel formulations of silver nanoparticles remain exciting if it is applicable for cosmetic purposes. This study proposes a value-added brand-new nanomaterial for improving skin complexion by inhibiting melanin development. This work aims to develop cost effective, efficient, natural silver nanoparticles phytomediated by aqueous extract of leaf sheath scales of Cocos nucifera (Cn-AgNPs) having potential as tyrosinase inhibitors hindering melanin synthesis. The formation of Cn-AgNPs was assessed spectrophotometrically and confirmed by the sharp SPR spectrum at 425nm. The chemical composition profiling was characterized by X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. The morphology was confirmed by Field Emission Scanning Electron Microscopy (FESEM) and the thermal stability was assessed by Thermogravimetric analysis (TGA). Pharmacological application studies supported the materialization of Cn-AgNPs with significant antityrosinase potential and considerably improved antibacterial and antioxidant properties. Cn-AgNPs showed potential antibacterial effects against gram-positive and negative strains, including prominent infectious agents of the skin. Antioxidant capacity was confirmed with an IC50 of 57.8μg/mL by DPPH radical scavenging assay. Furthermore, in vitro melanin content determination was performed using SK-MEL cells. Cell line studies proved that Cn-AgNPs decrease the melanin content of cells. The IC50 value obtained was 84.82μg/mL. Hence Cn-AgNPs is proposed to be acting as a whitening agent through lessening cellular melanin content and as a significant inhibitor of tyrosinase activity. The antioxidant properties and antibacterial effects can contribute to skin rejuvenation and can prevent skin infections as well. This evidence proposes the development of a new nanostructured pharmaceutical and cosmetic formulation from Cocos nucifera leaf sheath scales.

Efficient polarization-insensitive quasi-BIC modulation by VO2 thin films.

Bound states in the continuum (BIC) offer great design freedom for realizing high-quality factor metasurfaces. By deliberately disrupting the inherent symmetries, BIC can degenerate into quasi-BIC exhibiting sharp spectra with strong light confinement. This transformation has been exploited to develop cutting-edge sensors and modulators. However, most proposed quasi-BICs in metasurfaces are composed of unit cells with Cs symmetry that may experience performance degradation due to polarization deviation, posing challenges in practical applications. Addressing this critical issue, our research introduces an innovative approach by incorporating metasurfaces with C4v unit cell symmetry to eliminate polarization response sensitivity. Vanadium Dioxide (VO2) is a phase-change material with a relatively low transition temperature and reversibility. Here, we theoretically investigate the polarization-insensitive quasi-BIC modulation in Si-VO2 hybrid metasurfaces. By introducing defects into metasurfaces with Cs, C4, and C4v symmetries, we enable the emergence of quasi-BICs characterized by strong Fano resonance in their transmission spectra. Via numerically calculating the multipole decomposition, distinct dominant multipoles for different quasi-BICs are identified. A comprehensive investigation into the polarization responses of these structures under varying directions of linearly polarized light reveals the superior polarization-independent characteristics of metasurfaces with C4 and C4v symmetries, a feature that ensures the maintenance of maximum resonance peaks irrespective of polarization direction. Utilizing the polarization-insensitive quasi-BIC, we thus designed two different Si-VO2 hybrid metasurfaces with C4v symmetry. Each configuration presents complementary benefits, leveraging the VO2 phase transition's loss change to facilitate efficient modulation. Our quantitative calculation indicates notable achievements in modulation depth, with a maximum relative modulation depth reaching up to 342%. For the first time, our research demonstrates efficient modulation using polarization-insensitive quasi-BICs in designed Si-VO2 hybrid metasurfaces, achieving identical polarization responses for quasi-BIC-based applications. Our work paves the way for designing polarization-independent quasi-BICs in metasurfaces and marks a notable advancement in the field of tunable integrated devices.

Spectrally Stable Deep-Blue Light-Emitting Diodes Based on Layer-Transferred Single-Crystalline Ruddlesden-Popper Halide Perovskites.

A novel approach to producing high-color-purity blue-light-emitting diodes based on single-crystalline Ruddlesden-Popper perovskites (RPPs) is reported. The utilization of a pure bromide composition eliminates any possibility of halide segregation, which can otherwise lead to undesired shifts in the emission wavelength or irreversible degradation of the spectral line width. Phase-pure PEA2MAPb2Br7 single crystals with a lateral size exceeding 1 cm2 can be synthesized using the inverse temperature crystallization method. To prepare RPP layers with a thickness of less than 50 nm, we employ a thinning process of the initially thick bulk crystals, followed by a dry-transfer process to place them onto a hole transport layer and an indium-tin-oxide-coated glass substrate. By utilizing polydimethylsiloxane as a handling layer, deformations of the bulk RPP crystal and exfoliated RPP layer, as well as the formation of defects such as pinholes, can be effectively suppressed. Subsequent depositions of an electron transport layer and a metal contact complete the fabrication of electroluminescence (EL) devices. The EL devices utilizing the single-crystalline RPP demonstrate excellent spectral stability across a broad range of the applied bias voltage spanning from 4.5 to 10 V, exhibiting a significantly narrow line width of 14 nm at an emission wavelength of 440 nm that can potentially cover 99.3% of the Rec. 2020 color gamut. The sharp EL emission spectrum can be effectively preserved, avoiding any broadening of the line width, by suppressing Joule heating throughout the device operation, in addition to the intrinsic stability of single-crystalline RPPs.

Microbubble resonators for photoacoustic and photothermal characterisation of nanoparticles suspensions

We discuss the implementation of Whispering Gallery Modes Microbubble resonators (MBRs) as unique platforms for photoacoustic (PA) detection and photothermal (PT) spectroscopy. In a first experiment, the MBR transducer allowed to detect the PA signal generated by a suspension of gold nanorods (GNRs) within its core, leveraging on the MBR sharp optical spectrum and high sensitivity towards mechanical perturbations. Both static and flow-cytometry configuration were tested, finding that the MBR mechanical modes help detection by decoupling the environmental noise from the PA oscillation. In a second experiment, the MBR transducer allowed to reconstruct the GNRs absorption spectrum through the photothermal (PT) conversion, leveraging on high sensitivity towards temperature variations. We verified the scattering-free nature of the detection by using milk-stained GNRs suspension. We also found that the active locking of the MBR resonance increases the system sensitivity by an order-of-magnitude. These results make MBRs interesting candidates for combined PA and PT characterisation of extremely small samples for medical diagnosis, quality controls in food safety and chemical production processes.

Millimeter-Sized K2MnF6:Si4+, NH4+ Red-Luminescent Crystals with High Absorption Efficiency (AEmax of 93.5%) and External Quantum Efficiency (EQEmax of 68.9%) Grown by Cooling-Induced Crystallization.

Luminescent bulk crystals exhibit fewer grain boundaries and defects compared with conventional microsized powdery ones. Herein, targeting Mn4+-activated fluoride crystals with a sharp line-type red luminescence spectrum, we propose a new cooling-induced crystallization method to grow the fluoride crystals. By this new method, we successfully grew millimeter-sized K2MnF6:Si4+, NH4+ crystals, featuring an AEmax (absorption efficiency) of 93.5% and an EQEmax (external quantum efficiency) of 68.9%, which are among the best values for Mn4+-activated fluoride red phosphors. The influence of doping Si4+ and/or NH4+ in K2MnF6 on the local coordination structure and luminescence properties was studied. The anomalous thermal quenching behaviors were discussed, the luminescence decay from the excited state was compared, and the origin for the high quantum efficiencies was analyzed.

Identification of Calcium and Magnesium in Medicine Using Plasma Laser Spectroscopy

The identification of magnesium (Mg) in pharmaceutical products was carried out using LIPS (Laser-Induced Plasma Spectroscopy). The lasers used in the research were Nd: YAG laser and CO2 laser. The sample used was a supplement tablet. The laser beam is directed and focused by a convex lens on the sample. The plasma beam is induced on the sample surface. The sharp and high-intensity emission spectrum detected using the Nd: YAG laser indicates the presence of Calcium (Ca) and Magnesium (Mg) in the sample. The results obtained were then compared with sample testing using a CO2 laser. The results of the Mg spectrum intensity were much higher using a CO2 laser.

Near-infrared electroluminescent device from Cr3+-doped β-Ga2O3 in metal-oxide-semiconductor structure

Near-infrared (NIR) light spectroscopy has been utilized generously in wide applications, especially for plant growth supplements. However, providing an NIR light-emitting device that has excellent thermal stability remains a formidable challenge, due to the inherent characteristics of semiconductor materials when exposed to temperature variations. Herein, we present our investigation on an NIR-emitting electroluminescent (EL) device based on a Cr3+-doped β-Ga2O3 fabricated on a silicon substrate. The β-Ga2O3 inherits excellent electrical properties that lead to satisfactory performance as an EL device. Due to the intermediate crystal field strength of incorporating Cr3+ ions in the β-Ga2O3 host, it emits both sharp and broadband spectrum attributed to the metal ions transition energy levels in the octahedral site. The dependence of EL spectroscopy on applied voltages, frequencies, and temperatures is investigated. The results revealed acceptable performance and thermal stability that are potentially used in harsh environmental conditions.

Large-Emitting-Area Quantum Dot Light-Emitting Diodes Fabricated by an All-Solution Process.

Quantum dots (QDs) have attracted a lot of attention over the past decades due to their sharp emission spectrum and color, which can be tuned by changing just the particle size and chromophoric stability. All these advantages of QDs make quantum dot light-emitting diodes (QLEDs) promising candidates for display and light-source applications. This paper demonstrates a large-emitting-area QLED fabricated by a full-solution process. This QLED is composed of indium tin oxide (ITO) as the anode, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) as the hole injection layer (HIL), and poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine (poly-TPD) as the hole-transport layer (HTL). The light-emitting layer (EML) is composed of green CdSe/ZnS quantum dots. By applying the ZnO nanoparticles as the electron-injection/transport layer, QLED devices are prepared under a full-solution process. The large-emitting-area QLED exhibits a low turn-on voltage of around 2~3 V, and the International Commission on Illumination (CIE) 1931 coordinate value of the emission spectrum was (0.31, 0.66). The large emitting area and the unique QLED structure of the device make it possible to apply these features to inkjet printing quantum dot light sources and quantum dot display applications.

Highly efficient and stable Cr3+-activated oxyfluoride near-infrared emitting phosphor for night vision and plant growth

Near-infrared (NIR) light sources have many potential applications in biological, night vision, food safety, and plant growth. In this study, we report a highly efficient and thermally stable NIR phosphor LiAl4(1-x)O6F:xCr3+ (in brief LAOF:Cr3+). Under 565 nm excitation, the optimal LAOF:1.1%Cr3+ phosphor shows two sharp line spectra (named Cr1) centered at 703 nm and 713 nm, and a broadband emission (named Cr2) centered at 770 nm, which is ascribed to the [AlO6] and [Al(O, F)6] octahedra in the LAOF structure. Its unique narrowband and broadband emission correspond well with the absorption band of far-red phytochrome pigments (PFR), suggesting the potential application in plant growth. The FWHM extends from 25 to 53 nm as rising the Cr3+ ions concentration, and the Cr2 emission becomes more and more conspicuous. The LAOF:1.1%Cr3+ phosphor exhibits a high internal quantum efficiency (IQE) and external quantum efficiency (EQE) of ∼83.0% and 36.4%, respectively. Moreover, the LAOF:1.1%Cr3+ phosphor has good thermal stability (84.3%@373 K). NIR pc-LED device manufactured with a 450 nm blue LED chip and LAOF:1.1%Cr3+ phosphor exhibits good NIR output power (31.07 mW@100 mA) and photoelectric efficiency (13.3%@10 mA). The findings suggest the LAOF:Cr3+ phosphor holds potential in NIR pc-LED applications.

Inverse design of distributed bragg reflector targeting a sharp reflectivity spectrum

Distributed Bragg reflectors (DBRs) have found applications in various fields, including optical communications, light generation, solar cells, and sensors. DBRs are also crucial in open-access Fabry‐Pérot microcavities for enhanced and spectrally tunable light-matter interactions. This document presents the inverse design, fabrication, and optical characterization of aperiodic Ta2O5/SiO2 multilayer DBR mirrors targeting a sharp reflectivity spectrum. The results were confirmed through simulations and experimental measurements. The proposed inverse design methodology can be used to develop DBRs for important technologies such as single-photon sources, polaritonic systems, and random laser generation.

Nonlinearly tunable Fano resonance in photonic crystal heterostructure with embedded a varactor-loaded split ring resonator

The study explores the Fano-type interference effect in a microstrip photonic crystal (PC) heterostructure integrated with a varactor-loaded split ring resonator (SRR), both experimentally and numerically. This effect capitalizes on the PC heterostructure’s ability to provide a broad continuous spectrum, while the embedded SRR offers a narrow discrete pathway. Through coherent interference between these elements, a sharp asymmetric Fano-type transmission spectrum emerges, accompanied by a notable group delay. Furthermore, the composite configuration exhibits an electric field enhancement at the Fano resonant frequency, enhancing the nonlinear sensitivity of the transmission spectrum. The nonlinear tunability of the Fano resonance is demonstrated by applying distinct input powers, allowing for the realization of a high-performance bistable electromagnetic switch and diode in the microwave regime. The proposed configuration exhibits key features such as significant transmission contrast, low threshold intensity, and relatively high transmission amplitude, all within a compact device volume, thanks to the Fano resonant mechanism in the PC heterostructure. This design paves the way for the implementation of active metamaterials-assisted components in micro- or nano-photonic circuits, with potential applications in advanced optical devices.

Influence of γ-irradiation on the structural and optical properties of PVA/rGO films reinforced with rGO for nuclear shielding applications.

The polyvinyl alcohol films reinforced with reduced graphene oxide (PVA/rGO) have been synthesized by the film casting method. Fourier-transform infrared spectroscopy (FTIR) was used to measure the spectra for PVA/rGO films before and after being exposed to various dosages of γ-irradiation. XRD “X-ray diffraction” has been used to evaluate the structure of PVA/rGO before and after γ-ray irradiation and showed the potential for some H-bonding to be broken along with the splitting of the major chain. When compared to the non-irradiated sample, the FT-IR spectra of the irradiated samples show clear variations in peak locations and intensities. The absorbance spectral behavior of PVA/rGO film before and after irradiation with γ-rays at different dosages demonstrates a sharp and intense absorption spectrum centered at 205 nm and abroad, as well as a weak absorption spectrum centered at 277 nm. The absorbance spectrum fitting (ASF), the first derivation of the absorption spectrum fitting (DASF), and Tauc's methods were studied to investigate the optical energy gap for the PVA/rGO films before and after γ-irradiation with varied gamma doses. Also, the linear refractive index (n) for γ-irradiated PVA/rGO films was estimated and shows an increase in the values as the γ-doses increased. Such results show the great potential of the PVA/rGO polymer film in photovoltaic, polymer science applications, and radiation shielding.

Fabrication of Cu grating guided-mode resonance filter by electroplating

A polarization wavelength filter was fabricated using two-beam interference and electroplating methods. The device consists of a Cu grating with a pitch of 400 nm on an ITO film. For normal incidence, the transverse magnetic (TM) transmission spectrum had a sharp spectrum at a wavelength of 648 nm and a significant dip at 735 nm. Furthermore, a sharp reflection spectrum in TM-light was obtained at a 685 nm wavelength and incident angle of 40°, and the peak wavelength shifted to a longer wavelength as the incident angle increased. This fabrication method is less complex and inexpensive than conventional methods.

Study of the Surface Plasmon Refractive Index Nanosensor Based on Fanoresonance

In order to solve the problems of low sensitivity and complex structure of surface –plasmon- polariton (SPP) sensor at the present stage, a highly sensitive and stable SPP sensor composed of metal-insulator-metal (MIM) waveguide, a stub and a resonant cavity is proposed. The diameter of the MIM waveguide is chosen to be 50 nm so that only the single mode exists. The radius and refractive index of the cavity can vary, which is imbedded in silver background so that SPP phenomenon can be produced. The optical transmission characteristics and sensing characteristics of the designed sensor are studied by using finite element method. Experimental results show that the combination of the MIM waveguide and the stub can produce continuous state and the cavity can produce discrete state at the wavelength of 830 nm. At the same time, our research also demonstrates the sharp asymmetric Fano transmission spectrum is also sensitive to the surrounding medium. The application of the designed device in the field of refractive index sensing is also studied by calculating the shift of the resonant wavelength with the change of the refractive index of the medium in the resonator. The device can achieve refractive index sensing performance with the sensitivity of 803 nm/RIU and the figure of merit of 121.

Enhanced microwave metrology using an optical grating in Rydberg atoms.

An enhanced measurement of the microwave (MW) electric (E) field is proposed using an optical grating in Rydberg atoms. Electromagnetically induced transparency (EIT) of Rydberg atoms appears driven by a probe field and a control field. The EIT transmission spectrum is modulated by an optical grating. When a MW field drives the Rydberg transition, the central principal maximum of the grating spectrum splits. It is interesting to find that the magnitude of the sharp grating spectrum changes linearly with the MW E-field strength, which can be used to measure the MW E-field. The simulation result shows that the minimum detectable E-field strength is nearly 1/8 of that without gratings, and its measurement accuracy could be enhanced by about 60 times. Other discussion of MW metrology based on a grating spectrum is also presented.

Holographic Lieb lattice and gapping its Dirac band

We first point out that the Laia-Tong model realizes the Lieb lattice in the holographic setup. It generates a flat band of sharp particle spectrum together with a Dirac band of unparticle spectrum. We provided an understanding why the Laia-Tong model’s boundary condition generate a flat band and compared it with the mechanism of “compact localized orbits” in the lattice models to provide a physical reason why Lieb and Laia-Tong model should be identified based on the similarity in the flat band generation mechanism. We then construct a model which opens a gap to the Dirac band so that one can realize a well-separated flat band. We then study the phase transition between the gapped and gapless phases analytically. We also made methodological progress to find a few other possible quantizations and we express the Green functions in any quantization in terms of that in the standard quantization. Finally we carried out the problem of back reaction to show that the qualitative feature remains the same.

Highly Efficient and Stable Blue OLEDs Based on B—N Bonds Embedded 6,12‐Diphenyl‐5,11‐dihydroindolo[3,2‐b]carbazole with Narrowband Emission and Extended Lifetime†

Comprehensive SummaryEmitters with narrowband spectra are of great importance nowadays because of the growing demand for ultra‐high‐definition displays in the fields of panel displays and solid‐state lighting. Though the reported multiple resonance (MR) emitters have been widely studied with extremely sharp spectra and color‐tunable emissions, the electrophilic borylation synthetic strategies and stable narrowband blue devices still face great challenges. Herein, by virtue of the advantages of both the MR effect of conventional indolocarbazole skeleton and the easy‐to‐access of B—N covalent bonds, the linear tert‐butyl benzene and carbazole groups modified 6,12‐diphenyl‐5,11‐dihydroindolo[3,2‐b]carbazole derivatives (tPh[BN] and Cz[BN]) containing two B—N covalent bonds are easily constructed through amine‐directed double borylation strategy. Both emitters behaved bright blue emission with full‐width‐at‐half‐maximum (FWHM) of 20—27 nm in solution, high fluorescence quantum efficiency over 90%, and excellent stability toward moisture. By employing triplet‐triplet annihilation electroluminescent mechanism, blue OLED devices based on them showed a small FWHM of 48 nm and maximum external quantum efficiency of ~7.1% with negligible efficiency roll‐off, and long operational lifetime (LT80) of 87 h at an initial brightness of 1000 cd·m−2, demonstrating the enormous application potential of B—N bonds embedded emitters in achieving ideal narrowband blue emitters.