Proton-conductive coordination polymer glass for solid-state anhydrous proton batteries

Designing solid-state electrolytes for proton batteries at moderate temperatures is challenging as most solid-state proton conductors suffer from poor moldability and thermal stability. Crystal–glass transformation of coordination polymers (CPs) and metal–organic frameworks (MOFs) via melt-quenching offers diverse accessibility to unique properties as well as processing abilities. Here, we synthesized a glassy-state CP, [Zn₃(H₂PO₄)₆(H₂O)₃](1,2,3-benzotriazole), that exhibited a low melting temperature (114 °C) and a high anhydrous single-ion proton conductivity (8.0 × 10⁻³ S cm⁻¹ at 120 °C). Converting crystalline CPs to their glassy-state counterparts via melt-quenching not only initiated an isotropic disordered domain that enhanced H⁺ dynamics, but also generated an immersive interface that was beneficial for solid electrolyte applications. Finally, we demonstrated the first example of a rechargeable all-solid-state H⁺ battery utilizing the new glassy-state CP, which exhibited a wide operating-temperature range of 25 to 110 °C.

Melt-quenched coordination polymer glass shows exclusive H⁺ conductivity (8.0 × 10⁻³ S cm⁻¹ at 120 °C, anhydrous) and optimal mechanical properties (42.8 Pa s at 120 °C), enables the operation of an all-solid-state proton battery from RT to 110 °C.     

Twist and sliding dynamics between interpenetrated frames in Ti-MOF revealing high proton conductivity

We report the design and synthesis of a titanium catecholate framework, MOF-217, comprised of 2,4,6-tri(3,4-dihydroxyphenyl)-1,3,5-triazine (TDHT) and isolated TiO₆ clusters, with 2-fold interpenetrated srs topology. The dynamics of the organic linker, breaking the C_3h symmetry, allowed for reversible twist and sliding between interpenetrated frames upon temperature change and the inclusion of small molecules. Introduction of 28 wt% imidazole into the pores of MOF-217, 28% Im-in-MOF-217, resulted in four orders of magnitude increase in proton conductivity, due to the appropriate accommodation of imidazole molecules and their proton transfer facilitated by the H-bond to the MOF structure across the pores. This MOF-based proton conductor can be operated at 100 °C with a proton conductivity of 1.1 × 10⁻³ S cm⁻¹, standing among the best performing anhydrous MOF proton conductors at elevated temperature. The interframe dynamics represents a unique feature of MOFs that can be accessed in the future design of proton conductors.

Twist and sliding dynamics observed in a titanium catecholate MOF induced by imidazole for efficient proton conduction.     

Critical Reappraisal of Methods for Measuring Urine Saturation with Calcium Salts

Background: Metabolic and physicochemical evaluation is recommended to manage the condition of patients with nephrolithiasis. The estimation of the saturation state (β values) is often included in the diagnostic work-up, and it is preferably performed through calculations. The free concentrations of constituent ions are estimated by considering the main ionic soluble complexes. It is contended that this approach is liable to an overestimation of β values because some complexes may be overlooked. A recent report found that β values could be significantly lowered upon the addition of new and so far neglected complexes, [Ca(PO₄)Cit]⁴⁻ and [Ca₂H₂(PO₄)₂]. The aim of this work was to assess whether these complexes can be relevant to explaining the chemistry of urine. Methods: The Ca–phosphate–citrate aqueous system was investigated by potentiometric titrations. The stability constants of the parent binary complexes [Cacit]⁻ and [CaPO₄]⁻, and the coordination tendency of PO₄³⁻ toward [Ca(cit)]⁻ to form the ternary complex, were estimated. β_CaOx and β_CaHPO4 were then calculated on 5 natural urines by chemical models, including or not including the [CaPO₄]⁻ and [Ca(PO₄)cit]⁴⁻ species. Results: Species distribution diagrams show that the [Ca(PO₄)cit]⁴⁻ species was only noticeable at pH > 8.5 and below 10% of the total calcium. β values estimated on natural urine were slightly lowered by the formation of [CaPO₄]⁻ species, whereas [Ca(PO₄)cit]⁴⁻ results were irrelevant. Conclusions: While [CaPO₄]⁻ species have an impact on saturation levels at higher pHs, the existence of ternary complex and of the dimer is rejected.     

Semiquinone radical-bridged M2 (M = Fe,Co, Ni) complexes with strong magnetic exchange giving rise to slow magnetic relaxation

The use of radical bridging ligands to facilitate strong magnetic exchange between paramagnetic metal centers represents a key step toward the realization of single-molecule magnets with high operating temperatures. Moreover, bridging ligands that allow the incorporation of high-anisotropy metal ions are particularly advantageous. Toward these ends, we report the synthesis and detailed characterization of the dinuclear hydroquinone-bridged complexes [(Me₆tren)₂M^II₂(C₆H₄O₂²⁻)]²⁺ (Me₆tren = tris(2-dimethylaminoethyl)amine; M = Fe, Co, Ni) and their one-electron-oxidized, semiquinone-bridged analogues [(Me₆tren)₂M^II₂(C₆H₄O₂⁻˙)]³⁺. Single-crystal X-ray diffraction shows that the Me₆tren ligand restrains the metal centers in a trigonal bipyramidal geometry, and coordination of the bridging hydro- or semiquinone ligand results in a parallel alignment of the three-fold axes. We quantify the p-benzosemiquinone–transition metal magnetic exchange coupling for the first time and find that the nickel(ii) complex exhibits a substantial J < −600 cm⁻¹, resulting in a well-isolated S = 3/2 ground state even as high as 300 K. The iron and cobalt complexes feature metal–semiquinone exchange constants of J = −144(1) and −252(2) cm⁻¹, respectively, which are substantially larger in magnitude than those reported for related bis(bidentate) semiquinoid complexes. Finally, the semiquinone-bridged cobalt and nickel complexes exhibit field-induced slow magnetic relaxation, with relaxation barriers of U_eff = 22 and 46 cm⁻¹, respectively. Remarkably, the Orbach relaxation observed for the Ni complex is in stark contrast to the fast processes that dominate relaxation in related mononuclear Ni^II complexes, thus demonstrating that strong magnetic coupling can engender slow magnetic relaxation.

A semiquinone radical bridging two trigonal bipyramidal metal centers facilitates strong magnetic exchange and single-molecule magnet behavior.     

An earth-abundant bimetallic catalyst coated metallic nanowire grown electrode with platinum-like pH-universal hydrogen evolution activity at high current density

A self-supported and flexible current collector solely made of earth-abundant elements, NiCo layered double hydroxide (LDH) wrapped around Cu nanowires (Cu-Ws) grown on top of commercially available Cu mesh (Cu-m), outperforms the benchmark 40 wt% Pt/C in catalyzing the electrochemical hydrogen evolution reaction (HER). The Cu-m/Cu-W/NiCo-LDH cathode operates both in acidic and alkaline media exhibiting high turnover frequencies (TOF) at 30 mV (0.3 H₂ s⁻¹ in 1 M KOH and 0.32 H₂ s⁻¹ in 0.5 M H₂SO₄, respectively) and minimal overpotentials of 15 ± 6 mV in 1 M KOH and 27 ± 2 mV in 0.5 M H₂SO₄ at −10 mA cm⁻². Cu-m/Cu-W/NiCo-LDH outperforms the activity of 40 wt% Pt/C that needs overpotentials of 22 and 18 mV in 1 M KOH and 0.5 M H₂SO₄, respectively. With a tremendous advantage over Pt/C in triggering proton reduction with fast kinetics, similar mass activity and pH-universality, the current collector demonstrates outstanding operational durability even at above −1 A cm⁻². The high density of electronic states near the Fermi energy level of Cu-Ws is found to be a pivotal factor for efficient electron transfer to the NiCo-LDH catalyst. This class of self-supported electrodes is expected to trigger rapid progress in developing high performance energy conversion and storage devices.

A flexible self-supported electrode made of earth-abundant elements, NiCo layered double hydroxide wrapped around Cu nanowires grown on Cu mesh, outperforms the benchmark 40 wt% Pt/C in catalyzing electrochemical hydrogen evolution reaction.     

Trends in trigonal prismatic Ln-[1]ferrocenophane complexes and discovery of a Ho3+ single-molecule magnet

Lanthanide metallocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to transition metal ions. Herein, we present a systematic study of the structural and magnetic properties of the ferrocenophanes, [LnFc₃(THF)₂Li₂]⁻, of the late trivalent lanthanide ions (Ln = Gd (1), Ho (2), Er (3), Tm (4), Yb (5), Lu (6)). One major structural trend within this class of complexes is the increasing diferrocenyl (Fc²⁻) average twist angle with decreasing ionic radius (r_ion) of the central Ln ion, resulting in the largest average Fc²⁻ twist angles for the Lu³⁺ compound 6. Such high sensitivity of the twist angle to changes in r_ion is unique to the here presented ferrocenophane complexes and likely due to the large trigonal plane separation enforced by the ligand (>3.2 Å). This geometry also allows the non-Kramers ion Ho³⁺ to exhibit slow magnetic relaxation in the absence of applied dc fields, rendering compound 2 a rare example of a Ho-based single-molecule magnet (SMM) with barriers to magnetization reversal (U) of 110–131 cm⁻¹. In contrast, compounds featuring Ln ions with prolate electron density (3–5) don''t show slow magnetization dynamics under the same conditions. The observed trends in magnetic properties of 2–5 are supported by state-of-the-art ab initio calculations. Finally, the magneto-structural relationship of the trigonal prismatic Ho-[1]ferrocenophane motif was further investigated by axial ligand (THF in 2) exchange to yield [HoFc₃(THF*)₂Li₂]⁻ (2-THF*) and [HoFc₃(py)₂Li₂]⁻ (2-py) motifs. We find that larger average Fc²⁻ twist angles (in 2-THF* and 2-py as compared to in 2) result in faster magnetic relaxation times at a given temperature.

Lanthanide ferrocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to iron ions.     

Thermodynamics Analysis and Removal of P in a P-(M)-H2O System

In order to efficiently remove phosphorus, thermodynamic equilibrium diagrams of the P-H₂O system and P-M-H₂O system (M stands for Fe, Al, Ca, Mg) were analyzed by software from Visual MINTEQ to identify the existence of phosphorus ions and metal ions as pH ranged from 1 to 14. The results showed that the phosphorus ions existed in the form of H₃PO₄, H₂PO₄⁻, HPO₄²⁻, and PO₄³⁻. Among them, H₂PO₄⁻ and HPO₄²⁻ were the main species in the acidic medium (99% at pH = 5) and alkaline medium (97.9% at pH = 10). In the P-Fe-H₂O system ((P) = 0.01 mol/L, (Fe³⁺) = 0.01 mol/L), H₂PO₄⁻ was transformed to FeHPO₄⁺ at pH = 0–7 due to the existence of Fe³⁺ and then transformed to HPO₄²⁻ at pH > 6 as the Fe³⁺ was mostly precipitated. In the P-Ca-H₂O system ((P) = 0.01 mol/L, (Ca²⁺) = 0.015 mol/L), the main species in the acidic medium was CaH₂PO₄⁺ and HPO₄²⁻, and then transformed to CaPO₄⁻ at pH > 7. In the P-Mg-H₂O system ((P) = 0.01 mol/L, (Mg²⁺) = 0.015 mol/L), the main species in the acidic medium was H₂PO₄⁻ and then transformed to MgHPO₄ at pH = 5–10, and finally transformed to MgPO₄⁻ as pH increased. The verification experiments (precipitation experiments) with single metal ions confirmed that the theoretical analysis could be used to guide the actual experiments.     

Synthesis and anhydrous proton conductivity of poly(5-vinyltetrazole) prepared by free radical polymerization

5-Vinyltetrazole (VT)-based polymer is mainly produced by ‘click chemistry’ from polyacrylonitrile due to the unavailability of 5-vinyltetrazole monomer, which usually produces copolymers of VT and acrylonitrile rather than pure poly(5-vinyltetrazole) (PVT). In present work, VT was synthesized from 5-(2-chloroethyl)tetrazole via dehydrochlorination. A series of PVT with different molecular weight were synthesized by normal free radical polymerization. The chemical structures of VT and PVT were characterized by ¹H NMR and FTIR. PVT without any doped acid exhibits certain proton conductivity at higher temperature and anhydrous state. The proton conductivity of PVT decreases at least 2 orders of magnitude after methylation of tetrazole. PVT and PVT/H₃PO₄ composite membranes are thermally stable up to 200 °C. The glass transition temperature (T_g) of PVT/xH₃PO₄ composite membranes is shifted from 90 °C for x = 0.5 to 55 °C for x = 1. The temperature dependence of DC conductivity for pure PVT exhibits a simple Arrhenius behavior in the temperature range of 90–160 °C, while PVT/xH₃PO₄ composite membranes with higher H₃PO₄ concentration can be fitted by Vogel–Tamman–Fulcher (VTF) equation. PVT/1.0H₃PO₄ exhibits an anhydrous proton conductivity of 3.05 × 10⁻³ at 110 °C. The transmission of the PVT/xH₃PO₄ composite membrane is above 85% in the wavelength of visible light and changes little with acid contents. Thus, PVT/xH₃PO₄ composite membranes have potential applications not only in intermediate temperature fuel cells but also in solid electrochromic device.     

Ion polarisation-assisted hydrogen-bonded ferroelectrics in liquid crystalline domains

An alkylamide-substituted (−NHCOC₁₀H₂₁) hydrogen-bonded dibenzo[18]crown-6 derivative (1) was prepared to stabilise the ionic channel structure in a discotic hexagonal columnar (Col_h) liquid crystal. The introduction of simple M⁺X⁻ salts such as Na⁺PF₆⁻ and K⁺I⁻ into the ionic channel of 1 enhanced the ionic conductivity of the Col_h phase of the M⁺·(1)·X⁻ salts, with the highest ionic conductivity reaching ∼10⁻⁶ S cm⁻¹ for K⁺·(1)·I⁻ and Na⁺·(1)·PF₆⁻ at 460 K, which was approximately 5 orders of magnitude higher than that of 1. The introduction of non-ferroelectric 1 into the ferroelectric N,N′,N′′-tri(tetradecyl)-1,3,5-benzenetricarboxamide (3BC) elicited a ferroelectric response from the mixed Col_h phase of (3BC)_x(1)_1−x with x = 0.9 and 0.8. The further doping of M⁺X⁻ into the ferroelectric Col_h phase of (3BC)_0.9(1)_0.1 enhanced the ferroelectric polarisation assisted by ion displacement in the half-filled ionic channel for the vacant dibenzo[18]crown-6 of (3BC)_0.9[(M⁺)_0.5·(1)·(X⁻)_0.5]_0.1.

An alkylamide-substituted (−NHCOC₁₀H₂₁) hydrogen-bonded dibenzo[18]crown-6 derivative (1) was prepared to stabilise the ionic channel structure in a discotic hexagonal columnar (Col_h) liquid crystal.     

Nitric oxide monooxygenation (NOM) reaction of cobalt-nitrosyl {Co(NO)}8 to CoII-nitrito {CoII(NO2−)}: base induced hydrogen gas (H2) evolution

Here, we report the nitric oxide monooxygenation (NOM) reactions of a Co^III-nitrosyl complex (1, {Co-NO}⁸) in the presence of mono-oxygen reactive species, i.e., a base (OH⁻, tetrabutylammonium hydroxide (TBAOH) or NaOH/15-crown-5), an oxide (O²⁻ or Na₂O/15-crown-5) and water (H₂O). The reaction of 1 with OH⁻ produces a Co^II-nitrito complex {3, (Co^II-NO₂⁻)} and hydrogen gas (H₂), via the formation of a putative N-bound Co-nitrous acid intermediate (2, {Co-NOOH}⁺). The homolytic cleavage of the O–H bond of proposed [Co-NOOH]⁺ releases H₂via a presumed Co^III-H intermediate. In another reaction, 1 generates Co^II-NO₂⁻ when reacted with O²⁻via an expected Co^I-nitro (4) intermediate. However, complex 1 is found to be unreactive towards H₂O. Mechanistic investigations using ¹⁵N-labeled-¹⁵NO and ²H-labeled-NaO²H (NaOD) evidently revealed that the N-atom in Co^II-NO₂⁻ and the H-atom in H₂ gas are derived from the nitrosyl ligand and OH⁻ moiety, respectively.

Base-induced hydrogen (H₂) gas evolution in the nitric oxide monoxygenation reaction.

As a radical species, nitric oxide (NO) has attracted great interest from the scientific community due to its major role in various physiological processes such as neurotransmission, vascular regulation, platelet disaggregation and immune responses to multiple infections.¹ Nitric oxide synthase (NOS),² and nitrite reductase (NiR)³ enzymes are involved in the biosynthesis of NO. NOSs produce NO by the oxidation of the guanidine nitrogen in l-arginine.⁴ However, in mammals and bacteria, NO₂⁻ is reduced to NO by NiRs in the presence of protons, i.e., NO₂⁻ + e⁻ + 2H⁺ → NO + H₂O.⁵ Biological dysfunctions may cause overproduction of NO, and being radical it leads to the generation of reactive nitrogen species (RNS), i.e., peroxynitrite (PN, OONO⁻)⁶ and nitrogen dioxide (˙NO₂),⁷ upon reaction with reactive oxygen species (ROS) such as superoxide (O₂˙⁻),⁸ peroxide (H₂O₂),⁹ and dioxygen (O₂).¹⁰ Hence, it is essential to maintain an optimal level of NO. In this regard, nitric oxide dioxygenases (NODs)¹¹ are available in bio-systems to convert excess NO to biologically benign nitrate (NO₃⁻).¹²NO₂⁻ + Fe^II + H⁺ ↔ NO + Fe^III + OH⁻1[M–NO]ⁿ + 2OH⁻ → [M–NO₂]⁽ⁿ⁻²⁾ + H₂O2NOD enzymes generate NO₃⁻ from NO;^11b,12−13 however, the formation of NO₂⁻ from NO is still under investigation. Clarkson and Bosolo reported NO₂⁻ formation in the reaction of Co^III-NO and O₂.¹⁴ Nam and co-workers showed the generation of Co^II-NO₂⁻ from Co^III-NO upon reaction with O₂˙⁻.¹⁵ Recently, Mondal and co-workers reported NO₂⁻ formation in the reaction of Co^II-NO with O₂.¹⁶ Apart from cobalt, the formation of Cu^II-NO₂⁻ was also observed in the reaction of Cu^I-NO and O₂.¹⁷ For metal-dioxygen adducts, i.e., Cr^III-O₂˙⁻ and Mn^IV-O₂²⁻, NOD reactions led to the generation of Cr^III-NO₂⁻ (ref. 18) and Mn^V O + NO₂⁻,¹⁹ respectively. However, the NOD reaction of Fe^III-O₂˙⁻ and Fe^III-O₂²⁻ with NO and NO⁺, respectively, generated Fe^III-NO₃⁻via Fe^IV O and ˙NO₂.²⁰ Ford suggested that the reaction of ferric-heme nitrosyl with hydroxide leads to the formation of NO₂⁻ and H⁺.¹² Lehnert and co-workers reported heme-based Fe-nitrosyl complexes²¹ showing different chemistries due to the Fe^II-NO⁺ type electronic structures. On the other hand, Bryan proposed that the one-electron reduction of NO₂⁻ to NO in ferrous heme protein is reversible (eqn (1)).²² Also, it is proposed that excess NO in biological systems is converted to NO₂⁻ and produces one equivalent of H⁺ upon reaction with ˙OH.²³ Previously reported reactivity of M–NOs of Fe²⁴ with OH⁻ suggested the formation of NO₂⁻ and one equivalent of H⁺, where H⁺ further reacts with one equivalent of OH⁻ and produces H₂O (eqn (2)).²⁵Here in this report, we explore the mechanistic aspects of nitric oxide monooxygenation (NOM) reactions of the Co^III-nitrosyl complex, [(12TMC)Co^III(NO⁻)]²⁺/{Co(NO)}⁸ (1),^15,26 bearing the 12TMC ligand (12TMC = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) with mono-oxygen reactive species (O²⁻, OH⁻ and H₂O) (Scheme 1). Complex 1 reacts with the base (OH⁻, tetrabutylammonium hydroxide (TBAOH)/or NaOH in the presence of 15-crown-5 as the OH⁻ source) and generates the corresponding Co^II-nitrito complex, [(12TMC)Co^II(NO₂⁻)]⁺ (3), with the evolution of hydrogen gas (H₂) via the formation of a plausible N-bound Co-nitrous acid intermediate ([Co-NOOH]⁺, 2) in CH₃CN at 273 K (Scheme 1, reaction (I)). Also, when 1 reacts with the oxide (O²⁻ or Na₂O in the presence of 15-crown-5), it generates the Co^II-nitrito complex (3) via a probable Co^I-nitro, [(12TMC)Co^I(NO₂⁻)] (4), intermediate (Scheme 1, reaction (II)); however, 1 does not react with water (Scheme 1, reaction (III)). Mechanistic investigations using ¹⁵N-labeled-¹⁵NO, D-labeled-NaOD and ¹⁸O-labelled-¹⁸OH⁻ demonstrated, unambiguously, that the N and O-atoms in the NO₂⁻ ligand of 3 resulted from NO and OH⁻ moieties; however, the H-atoms of H₂ are derived from OH⁻. To the extent of our knowledge, the present work reports the very first systematic study of Co^III-nitrosyl complex reactions with H₂O, OH⁻ and O²⁻. This new finding presents an alternative route for NO₂⁻ generation in biosystems, and also illustrates a new pathway of H₂ evolution, in addition to the reported literature.^12,27Open in a separate windowScheme 1Nitric oxide monooxygenation (NOM) reactions of cobalt-nitrosyl complex (1) in the presence of a base (OH⁻), sodium oxide (Na₂O) and water (H₂O).To further explore the chemistry of [(12TMC)Co^III(NO⁻)]²⁺ (1),^15,26 and the mechanistic insights of NOM reactions, we have reacted it with a base (OH⁻), an oxide (O²⁻), and water (H₂O). When complex 1 was reacted with TBAOH in CH₃CN, the color of complex 1 changed to light pink from dark pink. In this reaction, the characteristic absorption band of 1 (370 nm) disappears within 2 minutes (Fig. 1a; ESI, Experimental section (ES) and Fig. S1a^†), producing a Co^II-nitrito complex, [(12TMC)Co^II(NO₂⁻)]⁺ (3), with H₂ (Scheme 1, reaction (Ib)), in contrast to the previous reports on base induced NOM reactions (eqn (2)).^12,25,28 The spectral titration data confirmed that the ratio-metric equivalent of OH⁻ to 1 was 1 : 1 (ESI, Fig. S1b^†). 3 was determined to be [(12TMC)Co^II(NO₂⁻)](BF₄) based on various spectroscopic and structural characterization experiments (vide infra).^15,26bOpen in a separate windowFig. 1(a) UV-vis spectral changes of 1 (0.50 mM, black line) upon addition of OH⁻ (1 equiv.) in CH₃CN under Ar at 273 K. Black line (1) changed to red line (3) upon addition of OH⁻. Inset: IR spectra of 3-¹⁴NO₂⁻ (blue line) and 3-¹⁵NO₂⁻ (red line) in KBr. (b) ESI-MS spectra of 3. The peak at 333.2 is assigned to [(12TMC)Co^II(NO₂)]⁺ (calcd m/z 333.1). Inset: isotopic distribution pattern for 3-¹⁴NO₂⁻ (red line) and 3-¹⁵NO₂⁻ (blue line).The FT-IR spectrum of 3 showed a characteristic peak for nitrite stretching at 1271 cm⁻¹ (Co^II-14NO₂⁻) and shifted to 1245 cm⁻¹ (Co^II-15NO₂⁻) when 3 was prepared by reacting ¹⁵N-labeled NO (Co^III-15NO) with OH⁻ (Inset, Fig. 1a and Fig. S2^†). The shifting of NO₂⁻ stretching (Δ = 30 cm⁻¹) indicates that the N-atom in the NO₂⁻ ligand is derived from Co^III-15NO. The ESI-MS spectrum of 3 showed a prominent peak at m/z 333.2, [(12TMC)Co^II(¹⁴NO₂⁻)]⁺ (calcd m/z 333.2), which shifted to 334.2, [(12TMC)Co^II(¹⁵NO₂⁻)]⁺ (calcd m/z 334.2), when the reaction was performed with Co^III-15NO (Inset, Fig. 1b; ESI, Fig. S3a^†); indicating clearly that NO₂⁻ in 3 was derived from the NO moiety of 1. In addition, we have reacted 1 with Na¹⁸OH (ES and ESI^†), in order to follow the source of the second O-atom in 3-NO₂⁻. The ESI-MS spectrum of the reaction mixture, obtained by reacting 1 with Na¹⁸OH, showed a prominent peak at m/z 335.2, [(12TMC)Co^II(¹⁸ONO⁻)]⁺ (calcd m/z 335.2), (SI, Fig. S3b^†) indicating clearly that NO₂⁻ in 3 was derived from ¹⁸OH⁻. The ¹H NMR spectrum of 3 did not show any signal for aliphatic protons of the 12TMC ligand, suggesting a bivalent cobalt center (Fig. S4^†).^26b Furthermore, we have determined the magnetic moment of 3, using Evans'' method, and it was found to be 4.62 BM, suggesting a high spin Co(ii) metal center with three unpaired electrons (ESI^† and ES).²⁹ The exact conformation of 3 was provided by single-crystal X-ray crystallographic analysis (Fig. 2b, ESI, ES, Fig. S5, and Tables T1 and T2^†) and similar to that of previously reported Co^II-NO₂⁻/M^II-NO₂⁻.^15,26b Also, we have quantified the amount of nitrite (90 ± 5%), formed in the above reaction, using the Griess reagent (ESI, ES, and Fig. S6^†).Open in a separate windowFig. 2Displacement ellipsoid plot (20% probability) of 3 at 100 K. Disordered C-atoms of the TMC ring, anion and H-atoms have been removed for clarity.As is known from the literature, a metal-nitrous acid intermediate may form either by the reaction of a metal-nitrosyl with a base²⁷ or by the metal-nitrite reaction with an acid (nitrite reduction chemistry);^26b however, the products of both the reactions are different. Here, for the first time, we have explored the reaction of Co^III-nitrosyl (1) with a base. In this reaction, it is clear that the formation of Co^II-nitrito would be accomplished by the release of H₂ gas via the generation of a transient N-bound [Co-(NOOH)]⁺ intermediate (Scheme 2, reaction (II)). The formation of Co^II-NO₂⁻ (3) from the [Co-(NOOH)]⁺ intermediate is likely to proceed by either (i) homolytic cleavage of the O–H bond and release of H₂via the proposed Co^III-H transient species (Co^III-H = Co^II + 1/2H₂)³⁰ (Scheme 2, reaction (III)), as reported in previous literature where the reduced cobalt, in a number of different ligand environments, is a good H⁺ reduction catalyst and generates H₂ gas via a Co^III-H intermediate³¹ or (ii) heterolytic cleavage of the O–H bond and the formation of Co^I-NO₂⁻ + H⁺.²⁷ In the present study, we observed the formation of 3 and H₂via the plausible homolytic cleavage of the NOO–H moiety of 2 as shown in Scheme 2, in contrast to the previous reports on base-induced reactions on metal-nitrosyls (eqn (3)).²⁷ Taking together both possibilities, (i) is the most reasonable pathway for the NOM reaction of complex 1 in the presence of a base (as shown in Scheme 2, reaction (III)). And the reaction is believed to go through a Co^III-H intermediate as reported previously in Co^I-induced H⁺ reduction in different ligand frameworks and based on literature precedence, we believe that complex 1 acts in a similar manner.³¹Open in a separate windowScheme 2NOM reaction of complex 1 in the presence of OH⁻, showing the generation of Co^II-nitrito (3) and H₂via a Co(iii)-hydrido intermediate.In contrast to an O-bound Co^II-ONOH intermediate, where N–O bond homolysis of the ON-OH moiety generates H₂O₂ (Scheme 2, reaction (IV)),^26b the N-bound [Co-(NOOH)]⁺ intermediate decomposes to form NO₂⁻ and a Co(iii)-H transient species, arising from β-hydrogen transfer from the NOO–H moiety to the cobalt-center (Scheme 2, reaction (II)).^30a,c,32 The Co(iii)-hydrido species may generate H₂ gas either (a) by its transformation to the Co(ii)-nitrito complex (2) and H₂ gas as observed in the case of Co^III-H intermediate chemistry^30a,c,e−g as proposed in the chemistry of the Co^I complex with H⁺ reduction³¹ and other metal-hydrido intermediates³² and also explained in O₂ formation in PN chemistry^17,33 or (b) by the reacting with another [Co-(NOOH)]⁺ intermediate (Scheme 2, reaction (III)).Furthermore, we have confirmed the H₂ formation in the NOM reaction of 1 with OH⁻ by headspace gas mass spectrometry (Fig. 3a). Also, carrying out the reaction of 1 with NaOD leads to the formation of the [Co-(NOOD)]⁺ intermediate, which then transforms to a Co^III-D transient species. Further, as described above, the Co^III-D species releases D₂ gas, detected by headspace gas mass spectrometry (Fig. 3b), which evidently established that H₂ gas formed in the reaction of 1 with OH⁻. In this regard, we have proposed that in the first step of this reaction, the nucleophilic addition of OH⁻ to {Co-NO}⁸ generates a transient N-bound [Co-(NOOH)]⁺ intermediate that is generated by an internal electron transfer to Co^III (Scheme 2, reaction (I)). By following the mechanism proposed in the case of Co^III-H,^30a−c O₂,¹⁵ and H₂O₂(ref. 26b) formation, we have proposed the sequences of the NOM reaction of 1, which leads to the generation of Co^II-nitrito and H₂ (Scheme 2, reaction (I)–(III) and Scheme 3). In the second step, O–H bond homolytic cleavage generates a Co^III-H transient species + NO₂⁻via a β-hydrogen elimination reaction of the [Co-(NOOH)]⁺ intermediate.³² The Co^III-H intermediate may undergo the following reactions to generate H₂ gas and Co^II-nitrito either (a) by the natural decomposition of the Co^III-H transient species to generate H₂,^30a,c,e−g or (b) by the H-atom abstraction from another [Co-(NOOH)]⁺ intermediate (Scheme 3). Also, to validate our assumption that the reaction goes through a plausible N-bound [Co-(NOOH)]⁺ intermediate followed by its transformation to the Co^III-H species (vide supra), we have performed the reaction of 1 with NaOH/NaOD (in 1 : 1 ratio). In this reaction, we have observed the formation of a mixture of H₂, D₂, and HD gases, which indicates clearly that the reaction goes through the formation of Co^III-H and Co^III-D transient species via the aforementioned mechanism (Fig. 3c). This is the only example where tracking of the H atoms has confirmed the H₂ generation from an N-bound NOO–H moiety as proposed for H₂ formation from Co^III-H.³⁰Open in a separate windowFig. 3Mass spectra of formation of (a) H₂ in the reaction of 1 (5.0 mM) with NaOH (5.0 mM), (b) D₂ in the reaction of 1 (5.0 mM) with NaOD (5.0 mM), (c) D₂, HD, and H₂ in the reaction of 1 (5.0 mM) with NaOD/NaOH (1 : 1), and (d) H₂ in the reaction of 1 (5.0 mM) with NaOH in the presence of 2,4 DTBP (50 mM).Open in a separate windowScheme 3NOM reaction of complex 1 in the presence of OH⁻, showing the different steps of the reaction.While, we do not have direct spectral evidence to support the formation of the transient N-bound [Co-(NOOH)]⁺ intermediate and its decomposition to the Co^III-H transient species via β-hydrogen transfer from the NOOH moiety to the cobalt center, support for its formation comes from our finding that the reactive hydrogen species can be trapped by using 2,4-di-tert-butyl-phenol (2,4-DTBP).³⁴ In this reaction, we observed the formation of 2,4-DTBP-dimer (2,4-DTBP-D, ∼67%) as a single product (ESI, ES, and Fig. S7^†). This result can readily be explained by the H-atom abstraction reaction of 2,4-DTBP either by [Co-(NOOH)]⁺ or Co^III-H, hence generating a phenoxyl-radical and 3 with H₂ (Fig. 3d and Scheme 2, reaction (a)). Also, we have detected H₂ gas formation in this reaction (ESI,^† ES, and Fig. 3d). In the next step, two phenoxyl radicals dimerized to give 2,4-DTBP-dimer (Scheme 2c, reaction (II)). Thus, the observation of 2,4-DTBP-dimer in good yield supports the proposed reaction mechanism (Scheme 2, reaction (a) and (b)). Further, the formation of 2,4 DTBP as a single product also rules out the formation of the hydroxyl radical as observed in the case of an O-bound nitrous acid intermediate.^26bFurthermore, we have explored the NOM reactivity of 1 with Na₂O/15-crown-5 (as the O²⁻ source) and observed the formation of the Co^II-nitrito complex (3) via a plausible Co^I-nitro (4) intermediate (Scheme 1, reaction (IIa); also see the ESI^† and ES); however, 1 was found to be inert towards H₂O (Scheme 1, reaction (III); also see the ESI, ES and Fig. S8^†). The product obtained in the reaction of 1 with O²⁻ was characterized by various spectroscopic measurements.^15,26b The UV-vis absorption band of 1 (λ_max = 370 nm) disappears upon the addition of 1 equiv. of Na₂O and a new band (λ_max = 535 nm) forms, which corresponds to 3 (ESI, Fig. S9^†). The FT-IR spectrum of the isolated product of the above reaction shows a characteristic peak for Co^II-bound nitrite at 1271 cm⁻¹, which shifts to 1245 cm⁻¹ when exchanged with ¹⁵N-labeled-NO (¹⁵N¹⁶O) (ESI, ES, and Fig. S10^†), clearly indicating the generation of nitrite from the NO ligand of complex 1.^26b The ESI-MS spectrum recorded for the isolated product (vide supra) shows a prominent ion peak at m/z 333.1, and its mass and isotope distribution pattern matches with [(12-TMC)Co^II(NO₂)]⁺ (calc. m/z 333.1) (ESI, Fig. S11^†). Also, we quantified the amount of 3 (85 ± 5%) by quantifying the amount of nitrite (85 ± 5%) using the Griess reagent test (ESI, ES, and Fig. S6^†).In summary, we have demonstrated the reaction of Co^III-nitrosyl, [(12-TMC)Co^III(NO⁻)]²⁺/{CoNO}⁸ (1), with mono-oxygen reactive species (O²⁻, OH⁻ and H₂O) (Scheme 1). For the first time, we have established the clear formation of a Co^II-nitrito complex, [(12TMC)Co^II(NO₂⁻)]⁺ (3), and H₂ in the reaction of 1 with one equivalent of OH⁻via a transient N-bound [Co-(NOOH)]⁺ (2) intermediate. This [Co-(NOOH)]⁺ intermediate undergoes the O–H bond homolytic cleavage and generates a Co^III-H transient species with NO₂⁻, via a β-hydrogen elimination reaction of the [Co-(NOOH)]⁺ intermediate, which upon decomposition produces H₂ gas. This is in contrast to our previous report, where acid-induced nitrite reduction of 3 generated 1 and H₂O₂via an O-bound Co^II-ONOH intermediate.^26b Complex 1 was found to be inert towards H₂O; however, we have observed the formation of 3 when reacted with O²⁻. It is important to note that H₂ formation involves a distinctive pathway of O–H bond homolytic cleavage in the [Co-(NOOH)]⁺ intermediate, followed by the generation of the proposed Co^III-H transient species (Co^II + 1/2H₂)³⁰ prior to H₂ evolution as described in Co^I chemistry with H⁺ in many different ligand frameworks.³¹ The present study is the first-ever report where the base induced NOM reaction of Co^III-nitrosyl (1) leads to Co^II-nitrito (3) with H₂ evolution via an N-bound [Co-(NOOH)]⁺ intermediate, in contrast to the chemistry of O-bound Co^II-ONOH^26b, hence adding an entirely new mechanistic insight of base induced H₂ gas evolution and an additional pathway for NOM reactions.     

Pore Geometry and Surface Engineering of Covalent Organic Frameworks for Anhydrous Proton Conduction

Developing new materials for anhydrous proton conduction under high-temperature conditions is significant and challenging. Herein, we create a series of highly crystalline covalent organic frameworks (COFs) via a pore engineering approach. We simultaneously engineer the pore geometry (generating concave dodecagonal nanopores) and pore surface (installing multiple functional groups such as −C=N−, −OH, −N=N− and −CF₃) to improve the utilization efficiency and host–guest interaction of proton carriers, hence benefiting the enhancement of anhydrous proton conduction. Upon loading with H₃PO₄, COFs can realize a proton conductivity of 2.33×10⁻² S cm⁻¹ under anhydrous conditions, among the highest values of all COF materials. These materials demonstrate good stability and maintain high proton conductivity over a wide temperature range (80–160 °C). This work paves a new way for designing COFs for anhydrous proton conduction applications, which shows great potential as high-temperature proton exchange membranes.     

Anhydrous proton conducting membranes based on crosslinked graft copolymer electrolytes

A comb-like copolymer consisting of a poly(vinylidene fluoride-co-chlorotrifluoroethylene) backbone and poly(hydroxy ethyl acrylate) side chains, i.e. P(VDF-co-CTFE)-g-PHEA, was synthesized through atom transfer radical polymerization (ATRP) using CTFE units as a macroinitiator. Successful synthesis and a microphase-separated structure of the copolymer were confirmed by proton nuclear magnetic resonance (¹H NMR), FT-IR spectroscopy, and transmission electron microscopy (TEM). This comb-like polymer was crosslinked with 4,5-imidazole dicarboxylic acid (IDA) via the esterification of the –OH groups of PHEA and the –COOH groups of IDA. Upon doping with phosphoric acid (H₃PO₄) to form imidazole–H₃PO₄ complexes, the proton conductivity of the membranes continuously increased with increasing H₃PO₄ content. A maximum proton conductivity of 0.015 S/cm was achieved at 120 °C under anhydrous conditions. In addition, these P(VDF-co-CTFE)-g-PHEA/IDA/H₃PO₄ membranes exhibited good mechanical properties (765 MPa of Young's modulus), and high thermal stability up to 250 °C, as determined by a universal testing machine (UTM) and thermal gravimetric analysis (TGA), respectively.     

Structure,Luminescent Sensing and Proton Conduction of a Boiling-Water-Stable Zn(II) Metal-Organic Framework

A novel Zn(II) metal-organic framework [Zn₄O(C₃₀H₁₂F₄O₄S₈)₃]_n, namely ZnBPD-4F4TS, has been constructed from a fluoro- and thiophenethio-functionalized ligand 2,2′,5,5′-tetrafluoro-3,3′,6,6′-tetrakis(2-thiophenethio)-4,4′-biphenyl dicarboxylic acid (H₂BPD-4F4TS). ZnBPD-4F4TS shows a broad green emission around 520 nm in solid state luminescence, with a Commission International De L’Eclairage (CIE) coordinate at x = 0.264, y = 0.403. Since d¹⁰-configured Zn(II) is electrochemically inert, its photoluminescence is likely ascribed to ligand-based luminescence which originates from the well-conjugated system of phenyl and thiophenethio moieties. Its luminescent intensities diminish to different extents when exposed to various metal ions, indicating its potential as an optical sensor for detecting metal ion species. Furthermore, ZnBPD-4F4TS and its NH₄Br-loaded composite, NH₄Br@ZnBPD-4F4TS, were used for proton conduction measurements in different relative humidity (RH) levels and temperatures. Original ZnBPD-4F4TS shows a low proton conductivity of 9.47 × 10⁻¹⁰ S cm⁻¹ while NH₄Br@ZnBPD-4F4TS shows a more than 25,000-fold enhanced value of 2.38 × 10⁻⁵ S cm⁻¹ at 40 °C and 90% RH. Both of the proton transport processes in ZnBPD-4F4TS and NH₄Br@ZnBPD-4F4TS belong to the Grotthuss mechanism with E_a = 0.40 and 0.32 eV, respectively.     

Preparation and Characterization of Highly Proton-Conductive Composites Composed of Phosphoric Acid-Doped Silica Gel and Styrene-Ethylene-Butylene-Styrene Elastomer

Highly proton-conductive elastic composites have been successfully prepared from H₃PO₄-doped silica gel and a styrene-ethylene-butylene-styrene (SEBS) block elastic copolymer. Ionic conductivities of the composites depended on the concentration of H₃PO₄ and the heat treatment temperature of the H₃PO₄-doped silica gel. It was found that H₃PO₄ added is present mainly as free orthophosphoric acid in the silica gel. The composite composed of H₃PO₄-doped silica gel with a molar ratio of H₃PO₄/SiO₂ = 0.5 heat-treated at temperatures below 200°C and SEBS elastomer in 5 mass% showed a high conductivity of 10^–5 S cm^–1 at 25°C in an dry N₂ atmosphere. The water adsorption during a storage in 25% relative humidity at room temperature for 1 day enhanced the ionic conductivities of composites by about one order of magnitude. Lower conductivities obtained in the composite with the H₃PO₄-doped silica gel heat-treated at 250°C for 1 h were due to the formation of crystalline Si₃(PO₄)₄. The temperature dependence of conductivity of the composites was the Vogel-Tamman-Fulcher type, indicating that proton was transferred through a liquidlike phase formed in micropores of the H₃PO₄-doped silica gels. The temperature dependence of the modulus of the composite was similar to that of the SEBS elastomer. The thermoplastically deforming temperature of the composite was around 100°C, which was higher by 30°C than that of the SEBS elastomer.     

Modulating the ground state,stability and charge transport in OFETs of biradicaloid hexahydro-diindenopyrene derivatives and a proposed method to estimate the biradical character

Biradicaloid compounds with an open-shell ground state have been the subject of intense research in the past decade. Although diindenoacenes are one of the most developed families, only a few examples have been reported as active layers in organic field-effect transistors (OFETs) with a charge mobility of around 10⁻³ cm² V⁻¹ s⁻¹ due to a steric disadvantage of the mesityl group to kinetically stabilize compounds. Herein, we disclose our efforts to improve the charge transport of the diindenoacene family based on hexahydro-diindenopyrene (HDIP) derivatives with different annelation modes for which the most reactive position has been functionalized with (triisopropylsilyl)ethynyl (TIPS) groups. All the HDIP derivatives show remarkably higher stability than that of TIPS-pentacene, enduring for 2 days to more than 30 days, which depends on the oxidation potential, the contribution of the singlet biradical form in the ground state and the annelation mode. The annelation mode affects not only the band gap and the biradical character (y₀) but also the value of the singlet–triplet energy gap (ΔE_S–T) that does not follow the reverse trend of y₀. A method based on comparison between experimental and theoretical bond lengths has been disclosed to estimate y₀ and shows that y₀ computed at the projected unrestricted Hartree–Fock (PUHF) level is the most relevant among those reported by all other methods. Thanks to their high stability, thin-film OFETs were successfully fabricated. Well balanced ambipolar transport was obtained in the order of 10⁻³ cm² V⁻¹ s⁻¹ in the bottom-gate/top-contact configuration, and unipolar transport in the top-gate/bottom-contact configuration was obtained in the order of 10⁻¹ cm² V⁻¹ s⁻¹ which is the highest value obtained for biradical compounds with a diindenoacene skeleton.

Biradicaloid HDIP derivatives show that the ΔE_S–T gap does not follow the reverse trend of the biradical character but depends more on the delocalization of the radical centres at the outer rings.     

Non-covalent assembly of proton donors and p-benzoquinone anions for co-electrocatalytic reduction of dioxygen

The two-electron and two-proton p-hydroquinone/p-benzoquinone (H₂Q/BQ) redox couple has mechanistic parallels to the function of ubiquinone in the electron transport chain. This proton-dependent redox behavior has shown applicability in catalytic aerobic oxidation reactions, redox flow batteries, and co-electrocatalytic oxygen reduction. Under nominally aprotic conditions in non-aqueous solvents, BQ can be reduced by up to two electrons in separate electrochemically reversible reactions. With weak acids (AH) at high concentrations, potential inversion can occur due to favorable hydrogen-bonding interactions with the intermediate monoanion [BQ(AH)_m]˙⁻. The solvation shell created by these interactions can mediate a second one-electron reduction coupled to proton transfer at more positive potentials ([BQ(AH)_m]˙⁻ + nAH + e⁻ ⇌ [HQ(AH)_(m+n)−1(A)]²⁻), resulting in an overall two electron reduction at a single potential at intermediate acid concentrations. Here we show that hydrogen-bonded adducts of reduced quinones and the proton donor 2,2,2-trifluoroethanol (TFEOH) can mediate the transfer of electrons to a Mn-based complex during the electrocatalytic reduction of dioxygen (O₂). The Mn electrocatalyst is selective for H₂O₂ with only TFEOH and O₂ present, however, with BQ present under sufficient concentrations of TFEOH, an electrogenerated [H₂Q(AH)₃(A)₂]²⁻ adduct (where AH = TFEOH) alters product selectivity to 96(±0.5)% H₂O in a co-electrocatalytic fashion. These results suggest that hydrogen-bonded quinone anions can function in an analogous co-electrocatalytic manner to H₂Q.

Non-covalent interactions between reduced p-benzoquinone species and weak acids stabilize intermediates which can switch dioxygen reduction selectivity from H₂O₂ to H₂O for a molecular Mn catalyst.     

Highly efficient H2S scavengers via thiolysis of positively-charged NBD amines

H₂S is a well-known toxic gas and also a gaseous signaling molecule involved in many biological processes. Advanced chemical tools that can regulate H₂S levels in vivo are useful for understanding H₂S biology as well as its potential therapeutic effects. To this end, we have developed a series of 7-nitro-1,2,3-benzoxadiazole (NBD) amines as potential H₂S scavengers. The kinetic studies of thiolysis reactions revealed that incorporation of positively-charged groups onto the NBD amines greatly increased the rate of the H₂S-specific thiolysis reaction. We demonstrate that these reactions proceed effectively, with second order rate constants (k₂) of >116 M⁻¹ s⁻¹ at 37 °C for NBD-S8. Additionally, we demonstrate that NBD-S8 can effectively scavenge enzymatically-produced and endogenous H₂S in live cells. Furthering the biological significance, we demonstrate NBD-S8 mediates scavenging of H₂S in mice.

We demonstrate that positively-charged NBD amines can effectively scavenge biological H₂S in live cells and in mice.     

The Synthesis of Poly(Vinyl Alcohol) Grafted with Fluorinated Protic Ionic Liquids Containing Sulfo Functional Groups

There has been an ongoing need to develop polymer materials with increased performance as proton exchange membranes (PEMs) for middle- and high-temperature fuel cells. Poly(vinyl alcohol) (PVA) is a highly hydrophilic and chemically stable polymer bearing hydroxyl groups, which can be further altered. Protic ionic liquids (proticILs) have been found to be an effective modifying polymer agent used as a proton carrier providing PEMs’ desirable proton conductivity at high temperatures and under anhydrous conditions. In this study, the novel synthesis route of PVA grafted with fluorinated protic ionic liquids bearing sulfo groups (–SO₃H) was elaborated. The polymer functionalization with fluorinated proticILs was achieved by the following approaches: (i) the PVA acylation and subsequent reaction with fluorinated sultones and (ii) free-radical polymerization reaction of vinyl acetate derivatives modified with 1-methylimidazole and sultones. These modifications resulted in the PVA being chemically modified with ionic liquids of protic character. The successfully grafted PVA has been characterized using ¹H, ¹⁹F, and ¹³C-NMR and FTIR-ATR. The presented synthesis route is a novel approach to PVA functionalization with imidazole-based fluorinated ionic liquids with sulfo groups.     

Bifunctional activation of amine-boranes by the W/Pd bimetallic analogs of “frustrated Lewis pairs”

The reaction between basic [(PCP)Pd(H)] (PCP = 2,6-(CH₂P(t-C₄H₉)₂)₂C₆H₄) and acidic [LWH(CO)₃] (L = Cp (1a), Tp (1b); Cp = η⁵-cyclopentadienyl, Tp = κ³-hydridotris(pyrazolyl)borate) leads to the formation of bimolecular complexes [LW(CO)₂(μ-CO)⋯Pd(PCP)] (4a, 4b), which catalyze amine-borane (Me₂NHBH₃, ^tBuNH₂BH₃) dehydrogenation. The combination of variable-temperature (¹H, ³¹P{¹H}, ¹¹B NMR and IR) spectroscopies and computational (ωB97XD/def2-TZVP) studies reveal the formation of an η¹-borane complex [(PCP)Pd(Me₂NHBH₃)]⁺[LW(CO₃)]⁻ (5) in the first step, where a BH bond strongly binds palladium and an amine group is hydrogen-bonded to tungsten. The subsequent intracomplex proton transfer is the rate-determining step, followed by an almost barrierless hydride transfer. Bimetallic species 4 are easily regenerated through hydrogen evolution in the reaction between two hydrides.

Bimetallic complexes [LW(CO)₂(μ-CO)⋯Pd(PCP)] cooperatively activate amine-boranes for their dehydrogenation via N–H proton tunneling at RDS and H₂ evolution from two neutral hydrides.     

Chiral polymer hosts for circularly polarized electroluminescence devices

Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications. The fabrication of a CP PLED requires a polymer host that provides the appropriate chiral environment around the emitting dopant. However, chemical strategies for the design of chiral polymer hosts remain underdeveloped. We have developed new polymer hosts for CP PLED applications. These polymers were prepared through a free-radical polymerization of 3-vinylcarbazole with a chiral N-alkyl unit. This chiral unit forces the carbazole repeat units to form mutually helical half-sandwich conformers with preferred (P)-helical sense along the polymer main chain. Electronic circular dichroism measurements demonstrate the occurrence of chirality transfer from chiral monomers to achiral monomers during chain growth. The (P)-helical-sense-enriched polymer interacts diastereoselectively with an enantiomeric pair of new phosphorescent (R)- and (S)-dopants. The magnitude of the Kuhn dissymmetry factor (g_abs) for the (P)-helically-enriched polymer film doped with the (R)-dopant was found to be one order of magnitude higher than that of the film doped with the (S)-dopant. Photoluminescence dissymmetry factors (g_PL) of the order of 10⁻³ were recorded for the doped films, but the magnitude of diastereomeric enhancement decreased to that of g_abs. The chiral polymer host permits faster energy transfer to the phosphorescent dopants than the achiral polymer host. Our photophysical and morphological investigations indicate that the acceleration in the chiral polymer host is due to its longer Förster radius and improved compatibility with the dopants. Finally, multilayer CP PLEDs were fabricated and evaluated. Devices based on the chiral polymer host with the (R)- and (S)-dopants exhibit electroluminescence dissymmetry factors (g_EL) of 1.09 × 10⁻⁴ and −1.02 × 10⁻⁴ at a wavelength of 540 nm, respectively. Although challenges remain in the development of polymer hosts for CP PLEDs, our research demonstrates that chiroptical performances can be amplified by using chiral polymer hosts.

Polymer electroluminescence devices producing circularly polarized luminescence (CP PLEDs) have valuable photonic applications.