BaP6N10NH:Eu2+ as a Case Study–An Imidonitridophosphate Showing Luminescence

Barium imidonitridophosphate BaP₆N₁₀NH was synthesized at 5 GPa and 1000 °C with a high-pressure high-temperature approach using the multianvil technique. Ba(N₃)₂, P₃N₅ and NH₄Cl were used as starting materials, applying a combination of azide and mineralizer routes. The structure elucidation of BaP₆N₁₀NH (P6₃, a=7.5633(11), c=8.512(2) Å, Z=2) was performed by a combination of transmission electron microscopy and single-crystal diffraction with microfocused synchrotron radiation. Phase purity was verified by Rietveld refinement. ¹H and ³¹P solid-state NMR and FTIR spectroscopy are consistent with the structure model. The chemical composition was confirmed by energy-dispersive X-ray spectroscopy and CHNS analyses. Eu²⁺-doped samples of BaP₆N₁₀NH show blue emission upon excitation with UV to blue light (λ_em=460 nm, fwhm=2423 cm⁻¹) representing unprecedented Eu²⁺-luminescence of an imidonitride.     

Luminescent Nitridophosphates CaP2N4:Eu2+, SrP2N4:Eu2+, BaP2N4:Eu2+, and BaSr2P6N12:Eu2+

Nitridophosphates MP₂N₄:Eu²⁺ (M=Ca, Sr, Ba) and BaSr₂P₆N₁₂:Eu²⁺ have been synthesized at elevated pressures and 1100–1300 °C starting from the corresponding azides and P₃N₅ with EuCl₂ as dopant. Addition of NH₄Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single‐crystal X‐ray diffraction data (CaP₂N₄:Eu²⁺ (P6₃, no. 173), a=16.847(2), c=7.8592(16) Å, V=1931.7(6) ų, Z=24, 2033 observed reflections, 176 refined parameters, wR₂=0.096). Upon excitation by UV light, luminescence due to parity‐allowed 4f⁶(⁷F)5d¹→4f⁷(⁸S_7/2) transition was observed in the orange (CaP₂N₄:Eu²⁺, λ_max=575 nm), green (SrP₂N₄:Eu²⁺, λ_max=529 nm), and blue regions of the visible spectrum (BaSr₂P₆N₁₂:Eu²⁺ and BaP₂N₄:Eu²⁺, λ_max=450 and 460 nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline‐earth ions. The corresponding full width at half maximum values (2240–2460 cm^?1) are comparable to those of other known Eu²⁺‐doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba₃P₅N₁₀Br:Eu²⁺, this investigation represents the first report on the luminescence of Eu²⁺‐doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu²⁺‐doped nitridophosphates may have the potential to be further developed into efficient light‐emitting diode phosphors.     

HIP to be Square: Simplifying Nitridophosphate Synthesis in a Hot Isostatic Press

(Oxo)Nitridophosphates have recently been identified as a promising compound class for application in the field of solid‐state lighting. Especially, the latest medium‐pressure syntheses under ammonothermal conditions draw attention of the semiconductor and lighting industry on nitridophosphates. In this contribution, we introduce hot isostatic presses as a new type of medium‐pressure synthetic tool, further simplifying nitridophosphate synthesis. In a second step, phosphorus nitride was replaced as starting material by red phosphorus, enabling the synthesis of Ca₂PN₃ as model compound, starting only from readily available compounds. Moreover, first luminescence investigations on Eu²⁺‐doped samples reveal Ca₂PN₃:Eu²⁺ as a promising broad‐band red‐emitter (λ_em=650 nm; fwhm=1972 cm^?1). Besides simple handling, the presented synthetic method offers access to large sample volumes, and the underlying reaction conditions facilitate single‐crystal growth, required for excellent optical properties.     

Synthesis and Luminescence Properties of Amber Emitting La7Sr[Si10N19O3] : Eu2+ and Syntheses of the Substitutional Variants RE8-xAEx[Si10N20-xO2+x] : Eu2+ with RE=La,Ce; AE=Ca,Sr, Ba; 0≤x≤2

The oxonitridosilicate La₇Sr[Si₁₀N₁₉O₃] : Eu²⁺ and its substitutional variants RE_8-xAE_x[Si₁₀N_20-xO_2+x] : Eu²⁺ with RE=La, Ce; AE=Ca, Sr, Ba and 0≤x≤2 were synthesized starting from REN, SrN/Ca₃N₂/Ba₂N, SiO₂, amorphous Si₃N₄ and Eu₂O₃ as doping agent at 1600 °C in a radiofrequency furnace. The crystal structure of La₇Sr[Si₁₀N₁₉O₃] was solved and refined based on single-crystal X-ray diffraction data. La₇Sr[Si₁₀N₁₉O₃] crystallizes in the orthorhombic space group Pmn2₁ (no. 31). The crystal structures of the isotypic compounds RE_8-xAE_x[Si₁₀N_20-xO_2+x] were confirmed by Rietveld refinements based on powder X-ray diffraction data using the single-crystal data of La₇Sr[Si₁₀N₁₉O₃] as starting point. Crystal structure elucidation reveals a 3D network of vertex sharing SiN₄ and SiN₂(N_1/2-x/4O_1/2+x/4)₂ (0≤x≤2) tetrahedra. When excited with UV to blue light, La₇Sr[Si₁₀N₁₉O₃] : Eu²⁺ shows amber luminescence with λ_em=612 nm and fwhm=84 nm/2194 cm⁻¹, which makes it interesting for application in amber phosphor-converted light emitting diodes.     

Missing Member in the MIIMIIISi4N7 Compound Class: Carbothermal Reduction and Nitridation Synthesis Reveal Substitution of Nitrogen by Carbon and Oxygen in CaLu[Si4N7–2xCxOx]:Eu2+/Ce3+ (x≈0.3)

The nitridosilicate CaLu[Si₄N_7–2xC_xO_x] (x≈0.3) was synthesized by carbothermal reduction and nitridation starting from CaH₂, Lu₂O₃, graphite and amorphous Si₃N₄ at 1550 °C in a radiofrequency furnace. CaLu[Si₄N_7–2xC_xO_x] (x≈0.3) crystallizes isotypically to many previously known M^IIM^IIISi₄N₇ compounds in the space group P6₃mc, as was confirmed by Rietveld refinement based on powder X-ray diffraction data. Incorporation of carbon into the crystal structure as a result of the carbothermal synthesis route was confirmed by ¹³C and ²⁹Si MAS NMR spectroscopy. For the first time in the M^IIM^IIISi₄N₇ compound class, complementary EDX measurements suggest that simultaneous incorporation of oxygen compensates for the negative charge excess induced by carbon, resulting in an adjusted sum formula, CaLu[Si₄N_7–2xC_xO_x] (x≈0.3). When excited with UV-to-blue light, CaLu[Si₄N_7–2xC_xO_x] (x≈0.3) shows an emission maximum in the blue spectral region (λ_em=484 nm; fwhm=4531 cm⁻¹) upon doping with Ce³⁺, whereas Eu²⁺-doped CaLu[Si₄N_7–2xC_xO_x] (x≈0.3) exhibits a yellow-green emission (λ_em=546 nm; fwhm=3999 cm⁻¹).     

Sr3P3N7: Complementary Approach by Ammonothermal and High-Pressure Syntheses

Nitridophosphates exhibit an intriguing structural diversity with different structural motifs, for example, chains, layers or frameworks. In this contribution the novel nitridophosphate Sr₃P₃N₇ with unprecedented dreier double chains is presented. Crystalline powders were synthesized using the ammonothermal method, while single crystals were obtained by a high-pressure multianvil technique. The crystal structure of Sr₃P₃N₇ was solved and refined from single-crystal X-ray diffraction and confirmed by powder X-ray methods. Sr₃P₃N₇ crystallizes in monoclinic space group P2/c. Energy-dispersive X-ray and Fourier-transformed infrared spectroscopy were conducted to confirm the chemical composition, as well as the absence of NH_x functionality. The optical band gap was estimated to be 4.4 eV using diffuse reflectance UV/Vis spectroscopy. Upon doping with Eu²⁺, Sr₃P₃N₇ shows a broad deep-red to infrared emission (λ_em=681 nm, fwhm≈3402 cm⁻¹) with an internal quantum efficiency of 42 %.     

High-Pressure High-Temperature Synthesis of Mixed Nitridosilicatephosphates and Luminescence of AESiP3N7:Eu2+ (AE=Sr,Ba)

Tetrahedra-based nitrides with network structures have emerged as versatile materials with a broad spectrum of properties and applications. Both nitridosilicates and nitridophosphates are well-known examples of such nitrides that upon doping with Eu²⁺ exhibit intriguing luminescence properties, which makes them attractive for applications. Nitridosilicates and nitridophosphates show manifold structural variability; however, no mixed nitridosilicatephosphates except SiPN₃ and SiP2N4NH have been described so far. The compounds AESiP₃N₇ (AE=Sr, Ba) were synthesized by a high-pressure high-temperature approach using the multianvil technique (8 GPa, 1400–1700 °C) starting from the respective alkaline earth azides and the binary nitrides P₃N₅ and Si₃N₄. The latter were activated by NH₄F, probably acting as a mineralizing agent. SrSiP₃N₇ and BaSiP₃N₇ were obtained as single crystals. They crystallized in the barylite-1O (M=Sr) and barylite-2O structure types (M=Ba), respectively, with P and Si being occupationally disordered. Cation disorder was further supported by solid-state NMR spectroscopy and energy-dispersive X-ray spectroscopy (EDX) mapping of BaSiP₃N₇ with atomic resolution. Upon doping with Eu²⁺, both compounds showed blue emission under UV excitation.     

Ultra‐Narrow‐Band Blue‐Emitting Oxoberyllates AELi2[Be4O6]:Eu2+ (AE=Sr,Ba) Paving the Way to Efficient RGB pc‐LEDs

Highly efficient phosphor‐converted light‐emitting diodes (pc‐LEDs) are popular in lighting and high‐tech electronics applications. The main goals of present LED research are increasing light quality, preserving color point stability and reducing energy consumption. For those purposes excellent phosphors in all spectral regions are required. Here, we report on ultra‐narrow band blue emitting oxoberyllates AELi₂[Be₄O₆]:Eu²⁺ (AE=Sr,Ba) exhibiting a rigid covalent network isotypic to the nitridoalumosilicate BaLi₂[(Al₂Si₂)N₆]:Eu²⁺. The oxoberyllates’ extremely small Stokes shift and unprecedented ultra‐narrow band blue emission with fwhm ≈25 nm (≈1200 cm^?1) at λ_em=454–456 nm result from its rigid, highly condensed tetrahedra network. AELi₂[Be₄O₆]:Eu²⁺ allows for using short‐wavelength blue LEDs (λ_em<440 nm) for efficient excitation of the ultra‐narrow band blue phosphor, for application in violet pumped white RGB phosphor LEDs with improved color point stability, excellent color rendering, and high energy efficiency.     

Post-Synthetic Modification: Systematic Study on a Simple Access to Nitridophosphates

Nitridophosphates are a well-studied class of nitrides with diverse materials properties, such as luminescence or ion conductivity. Despite the growing interest in this compound class, their synthesis mostly works through direct combination of starting materials. Herein, we present a systematic study on a promising method for post-synthetic modification by treating pre-synthesized nitridophosphates with halides under elevated pressures and temperatures. Herein, we focus on the applicability of this approach to P/N compounds with different degrees of condensation. Accordingly, BaP₂N₄, Ba₃P₅N₁₀Br, SrH₄P₆N₁₂, CaP₈N₁₄, and Ca₂PN₃ are investigated as model compounds for framework-, layer-, and chain-type nitridophosphates. The formation of structurally related, as well as, completely unrelated compounds, compared to the starting materials, shows the great potential of the approach, which increases the synthetic possibilities for nitridophosphates significantly.     

Inverse-Tunable Red Luminescence and Electronic Properties of Nitridoberylloaluminates Sr2−xBax[BeAl3N5]:Eu2+ (x=0–2)

The nitridoberylloaluminate Ba₂[BeAl₃N₅]:Eu²⁺ and solid solutions Sr_2−xBa_x[BeAl₃N₅]:Eu²⁺ (x=0.5, 1.0, 1.5) were synthesized in a hot isostatic press (HIP) under 50 MPa N₂ atmosphere at 1200 °C. Ba₂[BeAl₃N₅]:Eu²⁺ crystallizes in triclinic space group (no. 2) (Z=2, a=6.1869(10), b=7.1736(13), c=8.0391(14) Å, α=102.754(8), β=112.032(6), γ=104.765(7)°), which was determined from single-crystal X-ray diffraction data. The lattice parameters of the solid solution series have been obtained from Rietveld refinements and show a nearly linear dependence on the atomic ratio Sr : Ba. The electronic properties and the band gaps of M₂[BeAl₃N₅] (M=Sr, Ba) have been investigated by a combination of soft X-ray spectroscopy and density functional theory (DFT) calculations. Upon irradiation with blue light (440–450 nm), the nitridoberylloaluminates exhibit intense orange to red luminescence, which can be tuned between 610 and 656 nm (fwhm=1922–2025 cm⁻¹ (72–87 nm)). In contrast to the usual trend, the substitution of the smaller Sr²⁺ by larger Ba²⁺ leads to an inverse-tunable luminescence to higher wavelengths. Low-temperature luminescence measurements have been performed to exclude anomalous emission.     

Open‐Shell 3d Transition Metal Nitridophosphates MIIP8N14 (MII=Fe,Co, Ni) by High‐Pressure Metathesis

3d transition metal nitridophosphates M^IIP₈N₁₄ (M^II=Fe, Co, Ni) were prepared by high‐pressure metathesis indicating that this route might give a systematic access to a structurally rich family of M‐P‐N compounds. Their structures, which are stable in air up to at least 1273 K, were determined through powder X‐ray diffraction and consist of highly condensed tetra‐layers of PN₄ tetrahedra and MN₆ octahedra. Magnetic measurements revealed paramagnetic behavior of CoP₈N₁₄ and NiP₈N₁₄ down to low temperatures while, FeP₈N₁₄ exhibits an antiferromagnetic transition at T_N=3.5(1) K. Curie–Weiss fits of the paramagnetic regime indicate that the transition metal cations are in a oxidation state +II, which was corroborated by Mössbauer spectroscopy for FeP₈N₁₄. The ligand field exerted by the nitride ions in CoP₈N₁₄ and NiP₈N₁₄ was determined from UV/Vis/NIR data and is comparable to that of aqua‐ligands and oxophosphates.     

(BO)2-Doped Tetrathia[7]helicene: A Configurationally Stable Blue Emitter

Helicenes combine two central themes in chemistry: extended π-conjugation and chirality. Hetero-atom doping preserves both characteristics and allows modulation of the electronic structure of a helicene. Herein, we report the (BO)₂-doped tetrathia[7]helicene 1 , which was prepared from 2-methoxy-3,3′-bithiophene in four steps. 1 is formally derived by substituting two (Mes)B−O moieties in place of (H)C=C(H) fragments in two benzene rings of the parent tetrathia[7]helicene. X-ray crystallography revealed a dihedral angle of 50.26(9)° between the two terminal thiophene rings. The (P)-/(M)- 1 enantiomers were separated by chiral HPLC and are configurationally stable at room temperature. The experimentally determined enantiomerization barrier of 27.4±0.1 kcal mol⁻¹ is lower than that of tetrathia[7]helicene (39.4±0.1 kcal mol⁻¹). The circular dichroism spectra of (P)- and (M)- 1 show a perfect mirror-image relationship. 1 is a blue emitter (λ_em=411 nm) with a photoluminescence quantum efficiency of Φ_PL=6 % (cf. tetrathia[7]helicene: λ_em≈405 nm, Φ_PL=5 %).     

Host–Guest Recognition and Fluorescence of a Tetraphenylethene‐Based Octacationic Cage

We report the synthesis and characterization of a three‐dimensional tetraphenylethene‐based octacationic cage that shows host–guest recognition of polycyclic aromatic hydrocarbons (e.g. coronene) in organic media and water‐soluble dyes (e.g. sulforhodamine 101) in aqueous media through CH???π, π–π, and/or electrostatic interactions. The cage?coronene exhibits a cuboid internal cavity with a size of approximately 17.2×11.0×6.96 ų and a “hamburger”‐type host–guest complex, which is hierarchically stacked into 1D nanotubes and a 3D supramolecular framework. The free cage possesses a similar cavity in the crystalline state. Furthermore, a host–guest complex formed between the octacationic cage and sulforhodamine 101 had a higher absolute quantum yield (Φ_F=28.5 %), larger excitation–emission gap (Δλ_ex‐em=211 nm), and longer emission lifetime (τ=7.0 ns) as compared to the guest (Φ_F=10.5 %; Δλ_ex‐em=11 nm; τ=4.9 ns), and purer emission (Δλ_FWHM=38 nm) as compared to the host (Δλ_FWHM=111 nm).     

The missing link: triplet fluorocarbonyl nitrene FC(O)N

The elusive triplet fluorocarbonyl nitrene, FC(O)N (X³A′′), has been generated in high yield from matrix‐isolated FC(O)N₃ by ArF excimer laser photolysis (λ=193 nm). As a side product FNCO was formed. The novel nitrene was characterized by IR, UV/Vis, EPR spectroscopy, and quantum‐chemical calculations. All six fundamental vibrations of FC(O)N at 1681.3, 1193.8, 879.8, 646.5, 588.7, and 434.8 cm^?1 (argon matrix, 16 K), their ^12/13C, ^16/18O, and ^14/15N isotopic shifts, and four electronic transitions at T₀=13 890, 25 428, 29 166, and 30 900 cm^?1 that exhibit vibrational fine structures have been detected. Under visible‐light irradiation at λ≥495 nm, FC(O)N reacted with molecular N₂ in the matrix cage at 6 K to give back FC(O)N₃, whereas near‐UV irradiation at λ≥335 nm yielded FNCO. The singlet–triplet energy gaps of different carbonyl nitrenes are discussed.     

Phosphorescence at Low Temperature by External Heavy-Atom Effect in Zinc(II) Clusters

Luminescent Zn^II clusters [Zn₄L₄(μ₃-OMe)₂X₂] (X=SCN ( 1 ), Cl ( 2 ), Br ( 3 )) and [Zn₇L₆(μ₃-OMe)₂(μ₃-OH)₄]Y₂ (Y=I⁻ ( 4 ), ClO₄⁻ ( 5 )), HL=methyl-3-methoxysalicylate, exhibiting blue fluorescence at room temperature (λ_max=416≈429 nm, Φ_em=0.09–0.36) have been synthesised and investigated in detail. In one case the external heavy-atom effect (EHE) arising the presence of iodide counter anions yielded phosphorescence with a long emission lifetime (λ_max=520 nm, τ=95.3 ms) at 77 K. Single-crystal X-ray structural analysis and time-dependent density-functional theory (TD-DFT) calculations revealed that their emission origin was attributed to the fluorescence from the singlet ligand-centred (¹LC) excited state, and the phosphorescence observed in 4 was caused by the EHE of counter anions having strong CH−I interactions.     

Luminescence properties of Eu- and Ce-doped CaAl2S4 and application in white LEDs

The Eu²⁺- and Ce³⁺-doped CaAl₂S₄ phosphors were comparatively synthesized by conventional solid-state reaction and the evacuated sealed quartz ampoule. The X-ray diffraction (XRD) patterns show that the sample with better crystalline quality was prepared by the evacuated sealed quartz ampoule, resulting in the enhancement of the emission intensity of Eu²⁺ ion by a factor of 1.7. The intensive green LEDs were also fabricated by combining CaAl₂S₄:Eu²⁺ with near-ultraviolet InGaN chips (λ_em=395 nm). The dependence of as-fabricated green LEDs on forward-bias currents shows that it presents good chromaticity stability and luminance saturation, indicating that CaAl₂S₄:Eu²⁺ is a promising green-emitting phosphor for a near-UV InGaN-based LED. In addition, the optical properties of CaAl₂S₄:Ce³⁺ were systematically investigated by means of diffuse reflectance, photoluminescence excitation and emission, concentrating quenching and the decay curve.     

Environment‐Sensitive Fluorophores with Benzothiadiazole and Benzoselenadiazole Structures as Candidate Components of a Fluorescent Polymeric Thermometer

An environment‐sensitive fluorophore can change its maximum emission wavelength (λ_em), fluorescence quantum yield (Φ_f), and fluorescence lifetime in response to the surrounding environment. We have developed two new intramolecular charge‐transfer‐type environment‐sensitive fluorophores, DBThD‐IA and DBSeD‐IA, in which the oxygen atom of a well‐established 2,1,3‐benzoxadiazole environment‐sensitive fluorophore, DBD‐IA, has been replaced by a sulfur and selenium atom, respectively. DBThD‐IA is highly fluorescent in n‐hexane (Φ_f=0.81, λ_em=537 nm) with excitation at 449 nm, but is almost nonfluorescent in water (Φ_f=0.037, λ_em=616 nm), similarly to DBD‐IA (Φ_f=0.91, λ_em=520 nm in n‐hexane; Φ_f=0.027, λ_em=616 nm in water). A similar variation in fluorescence properties was also observed for DBSeD‐IA (Φ_f=0.24, λ_em=591 nm in n‐hexane; Φ_f=0.0046, λ_em=672 nm in water). An intensive study of the solvent effects on the fluorescence properties of these fluorophores revealed that both the polarity of the environment and hydrogen bonding with solvent molecules accelerate the nonradiative relaxation of the excited fluorophores. Time‐resolved optoacoustic and phosphorescence measurements clarified that both intersystem crossing and internal conversion are involved in the nonradiative relaxation processes of DBThD‐IA and DBSeD‐IA. In addition, DBThD‐IA exhibits a 10‐fold higher photostability in aqueous solution than the original fluorophore DBD‐IA, which allowed us to create a new robust molecular nanogel thermometer for intracellular thermometry.     

Unexpected Luminescence Properties of Sr0.25Ba0.75Si2O2N2:Eu2+—A Narrow Blue Emitting Oxonitridosilicate with Cation Ordering

Owing to a parity allowed 4f⁶(⁷F)5d¹→4f⁷(⁸S_7/2) transition, powders of the nominal composition Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺ (2 mol % Eu²⁺) show surprising intense blue emission (λ_em=472 nm) when excited by UV to blue radiation. Similarly to other phases in the system Sr_1?xBa_xSi₂O₂N₂:Eu²⁺, the described compound is a promising phosphor material for pc‐LED applications as well. The FWHM of the emission band is 37 nm, representing the smallest value found for blue emitting (oxo)nitridosilicates so far. A combination of electron and X‐ray diffraction methods was used to determine the crystal structure of Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺. HRTEM images reveal the intergrowth of nanodomains with SrSi₂O₂N₂ and BaSi₂O₂N₂‐type structures, which leads to pronounced diffuse scattering. Taking into account the intergrowth, the structure of the BaSi₂O₂N₂‐type domains was refined on single‐crystal diffraction data. In contrast to coplanar metal atom layers which are located between layers of condensed SiON₃‐tetrahedra in pure BaSi₂O₂N₂, in Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺ corrugated metal atom layers occur. HRTEM image simulations indicate cation ordering in the final structure model, which, in combination with the corrugated metal atom layers, explains the unexpected and excellent luminescence properties.     

Open‐Shell 3d Transition Metal Nitridophosphates MIIP8N14 (MII=Fe,Co, Ni) by High‐Pressure Metathesis

3d transition metal nitridophosphates M^IIP₈N₁₄ (M^II=Fe, Co, Ni) were prepared by high‐pressure metathesis indicating that this route might give a systematic access to a structurally rich family of M‐P‐N compounds. Their structures, which are stable in air up to at least 1273 K, were determined through powder X‐ray diffraction and consist of highly condensed tetra‐layers of PN₄ tetrahedra and MN₆ octahedra. Magnetic measurements revealed paramagnetic behavior of CoP₈N₁₄ and NiP₈N₁₄ down to low temperatures while, FeP₈N₁₄ exhibits an antiferromagnetic transition at T_N=3.5(1) K. Curie–Weiss fits of the paramagnetic regime indicate that the transition metal cations are in a oxidation state +II, which was corroborated by Mössbauer spectroscopy for FeP₈N₁₄. The ligand field exerted by the nitride ions in CoP₈N₁₄ and NiP₈N₁₄ was determined from UV/Vis/NIR data and is comparable to that of aqua‐ligands and oxophosphates.     

A π-Extended Pentadecabenzo[9]Helicene

A novel chiral nanographene (i.e. EP9H ) with a pentadecabenzo[9]helicene core fragment has been synthesized and fully characterized. Single-crystal X-ray diffraction unambiguously confirms the helical structure. The fluorescence emission of EP9H is located in the near infrared region (λ_em=684 nm) with a medium quantum yield (0.10) for helicene derivatives. Cyclic voltammetry reveals its seven quasi-reversible redox states from −2 to +5. Furthermore, enantiopure EP9H displays distinct CD signals in a broad spectral range from 300 to 700 nm. Notably, compared to the reported small organic molecules, EP9H displays an outstanding |g_lum| value of 4.50×10⁻² and B_CPL as 304 M⁻¹ cm⁻¹.