Stable Cation Research Articles

Engineering RHO Nanozeolite: Controlling the Particle Morphology, Al and Cation Content, Stability, and Flexibility

Engineering RHO Nanozeolite: Controlling the Particle Morphology, Al and Cation Content, Stability, and Flexibility

Poly(terphenyl piperidinium) containing hydrophilic crown ether units in main chains as anion exchange membranes for alkaline fuel cells and water electrolysers

Poly(arylene piperidinium) polymers are recognized as promising anion exchange membrane (AEM) materials for alkaline fuel cell and water electrolysis, due to the aryl-ether free polyaromatic backbones and stable piperidinium cations. Herein, hydrophilic crown ether units have been introduced into poly(terphenyl piperidinium) (PDTP) by readily superacid-catalyzed polycondensation of dibenzo-18-crown-6 (DE), p-terphenyl and N-methyl-4-piperidine followed via quaternization. The obtained PDTP membranes showed much higher hydroxide conductivity than the control poly(terphenyl piperidinium) (PTP) sample without DE units, due to their high water uptake. The highest hydroxide conductivity of 110 mS/cm was reached at 80 °C for PDTP-10 (where 10 denoted the molar content of crown ether units) membrane with an ion exchange capacity (IEC) of 2.57 meq./g. The introduction of DE units alleviated the chemical degradation of PDTP membrane in 1 M NaOH at 80 °C as compared to the PTP membranes. Furthermore, membrane electrode assemblies based on PDTP-10 membrane shown a peak power density of 621 mW/cm2 at 60 °C in AEM fuel cells and a current density of 2000 mA/cm2 at 2.1 V for water electrolysers circulated with 1 M NaOH at 80 °C. The in-situ stability tests in fuel cells and water electrolysers also manifested that the chemical structure of PDTP-10 membrane remained intact during short-term durability tests under galvanostatic mode. The above results manifested that AEMs containing hydrophilic crown ether units in the polymer mainchain showed potential in the application for AEM based electrochemical devices.

Direct ionization-driven observational approaches for radical cation formation in solution for pulse radiolysis

Radical cations’ dynamics in early stage reactions in the ionizing radiation induced reaction is essential to understanding the whole reaction scheme. The observation of radical cations in tetrahydrofuran (THF) solutions was demonstrated for time-resolved measurements using pulse radiolysis. The designedly concentrated solutions enabled the observation of the direct ionization-driven radical cations. In THF, the transient absorption spectra of the biphenyl radical cations, which were generated through direct ionization of biphenyl under electron beam irradiation, were found to be associated with the biphenyl radical anions generated by the attachment of an excess electron to the biphenyl. Furthermore, when polystyrene (PS) was used as the solute in THF solutions, transient absorption spectra of the dimer radical cations containing solvated electrons of PS were observed. The findings, therefore, indicate that the time-resolution-based limitation on the radical cation-forming process observation, which was imposed by the diffusion-limited reactions of the solvent radical cations with the solute, could be overcome by employing direct ionization in THF. This method can be employed to study the reactivity of radical cations with solvents and the stability of radical cations in fluid media.

More than Carbazole Derivatives Activate Room Temperature Ultralong Organic Phosphorescence of Benzoindole Derivatives.

The mechanism of carbazole (Cz)-based phosphors is still unclear since its isomer (1H-benzo[f]indole, Bd) is discovered in 2020. Herein, the successful synthesis of four Cz/Bd derivatives is reported, named as 2CzBr, CzBdBr, 2BdBr, and 3Bd, and the general mechanism for their ultralong organic phosphorescence (UOP) is provided. Bd and its derivatives give double groups of phosphorescence, including the short-wavelength phosphorescence with a short lifetime and the ultralong phosphorescence at long wavelengths, assigned to their neutral molecules and radical cations, respectively. Interestingly, the doped poly(methyl methacrylate) (PMMA) films of CzBdBr and 2BdBr show photo-activated ultralong phosphorescence at room temperature. The activation of Bd derivatives 'UOP involves three factors: 1) well dispersion in the matrix with limited amount, 2) generation of their radical cations and 3) the matrix-mediated stabilization of radical cations. The function of Cz derivatives to activate the Bd derivatives' UOP could be replaced by photo-activation or using other matrixes. Significantly, the application of the doped PMMA films is practiced and gives an exciting result that the high-resolution QR code could be reversibly printed and erased on the film. This research has expanded the understanding in the field of organic phosphorescence and it may pave a new way for its development.

A DFT study of the tautomerism of 1H-benzo[de]cinnolines and their protonated forms

1H-Benzo[de]cinnolines and 1H-indeno[6,7,1-def]cinnolines have been studied theoretically at the B3LYP/6-311++G(d,p) level in the gas-phase and in water solution (PCM model); gas-phase geometries were used to calculate absolute shieldings (GIAO) that were transformed into chemical shifts using empirical equations. The annular tautomerism of neutral species and of protonated cations have been determined, and the most stable cations coincide with those determined experimentally.

Supramolecular Salts of Fe(II)/Co(II)/Ni(II)/Cu(II)/Zn(II) 1,10‐Phenanthroline Cations and Similar Complex Tartratostannate(IV) Anions: From Structural Features to Antimicrobial Activity and Enzyme Activation

AbstractIn the present study authors establish the influence of complex cation on the structure formation, crystal packing, antimicrobial activity and enzyme activation of the previously described isostructural [M(phen)3]2[Sn2(μ‐Tart)2(H2Tart)2] complexes (M(II)=Fe(1), Co(2), Ni(3), Cu(4), Zn(5)). Despite the similarity of composition and structure, compounds 1–5 showed different level of antimicrobial activity. A certain pattern in their effectiveness – decreasing of minimal concentrations, resembles the Irving‐Williams series (Fe(II) < Co(II) < Ni(II) < Cu(II) > Zn(II)) and, according to the crystal field theory, correlates with the thermodynamic stability of octahedral cations [M(phen)3]2+. Quantum chemical calculations of cations revealed the insights of the “cations‐cell membranes” interactions and allowed authors to conclude that the cations in compounds 4 and 5 are the most lipophilic, have the highest affinity to the lipophilic cell membrane and, as a result, are more bioactive. It was established that compounds 1–5 had a different influence on the activity of studied α‐L‐rhamnosidases Penicillium tardum ІMB F‐100074 and Penicillium restrictum ІMB F‐100139. Correlation of these results with the crystal voids calculations and Hirshfeld surface analysis allow authors to suggest that presence of the bigger number of water molecules, generation of the branched network of hydrogen bonds and formation of active intermediate complex “enzyme – effector – substrate”, leads to the biggest intensification of activation properties for the compounds 2 and 5.

Quantum chemical studies of the electronic structures of anti-tumor agents: AuIIIL+ (L = porphine, tetraphenylporphyrin)

GoldIIImeso-tetraphenylporphyrin complexes are reported as one of potential anti-tumor drugs. Elucidation of the molecular properties and intermolecular interaction with amino acids are crucial in understanding their structure-function relationship and anti-tumor mechanism. In this study, we report quantum-chemical studies on the geometries, electronic structures, chemical bonding, and substituent effect of goldIII porphine cation and GoldIIImeso-tetraphenylporphyrin cation (AuTPP+). The stability of square planar D4h goldIII porphine cation primarily originates from the overlap between Au 5dx2-y2 and the ligand group orbitals of the nitrogen atoms of porphine. The electronic effect and the peripheral steric hindrance of the substituents present a combined influence on the geometry of the porphyrin core. Strong electron-donating group would prefer saddling distortion, while sterically hindered groups tend to cause ruffling distortion. The molecular-orbital (MO) energies of meso-substituted goldIII porphine generally increase from electron-withdrawing to electron-donating substituents, providing opportunity to tune the electronic properties of this kind of promising drugs. Through comprehensive screening of the interaction between AuTPP+ and various amino acids, we find dative interaction as well as potential π-π stacking dominant for AuTPP+ binding with amino acids. In particular, nitrogen atom of unprotonated histidine has been found to have a non-negligible dative bonding interaction with the central gold atom, which might be relevant to the anti-tumor functionality of AuTPP+.

Kinetics-Based Approach to Developing Electrocatalytic Variants of Slow Oxidations: Application to Hydride Abstraction-Initiated Cyclization Reactions.

Electrochemical oxidant regeneration is challenging in reactions that have a slow redox step because the steady-state concentration of the reduced oxidant is low, causing difficulties in maintaining sufficient current or preventing potential spikes. This work shows that applying an understanding of the relationship between intermediate cation stability, oxidant strength, overpotential, and concentration on reaction kinetics delivers a method for electrochemical oxoammonium ion regeneration in hydride abstraction-initiated cyclization reactions, resulting in the development of an electrocatalytic variant of a process that has a high oxidation transition state free energy. This approach should be applicable to expanding the scope of electrocatalysis to include additional slow redox processes.

Scale-up and mass transfer of the adsorption/desorption process of anthocyanins in amorphous silica

The purification and recovery of anthocyanins are important to maintain the stability of the purified solution, ensuring that the health-beneficial properties of this substance are not altered. This work aimed to obtain and compare solutions of commercial and natural grape and red cabbage anthocyanins, suitable process conditions, as well as purification and recovery through detailed analysis called two-stage, estimation of phenomenological parameters of mass transfer and scale-up using Bugram Protect® as amorphous silica. The adsorbent was characterized as amorphous and with a high silicon dioxide composition. The pH 3.0 potentiated the stability of flavylium cation in solution. The Freudlich isotherm represented the equilibrium data. The phenomenological parameters KE and Ds and the limiting step of mass transfer were estimated. Scale-up indicated dosages of adsorbents to meet the process specifications. This work presented additional results in phenomenological aspects and industrial scale in the recovery and purification of anthocyanins.

Sterically Stabilized Diblock Copolymer Nanoparticles Enable Convenient Preparation of Suspension Concentrates Comprising Various Agrochemical Actives.

It is well known that sterically stabilized diblock copolymer nanoparticles can be readily prepared using polymerization-induced self-assembly. Recently, we reported that such nanoparticles can be employed as a dispersant to prepare micron-sized particles of a widely used fungicide (azoxystrobin) via ball milling. In the present study, we examine the effect of varying the nature of the steric stabilizer block, the mean nanoparticle diameter, and the glass transition temperature (Tg) of the core-forming block on the particle size and colloidal stability of such azoxystrobin microparticles. In addition, the effect of crosslinking the nanoparticle cores is also investigated. Laser diffraction studies indicated the formation of azoxystrobin microparticles of approximately 2 μm diameter after milling for between 15 and 30 min at 6000 rpm. Diblock copolymer nanoparticles comprising a non-ionic steric stabilizer, rather than a cationic or anionic steric stabilizer, were determined to be more effective dispersants. Furthermore, nanoparticles of up to 51 nm diameter enabled efficient milling and ensured overall suspension concentrate stability. Moreover, crosslinking the nanoparticle cores and adjusting the Tg of the core-forming block had little effect on the milling of azoxystrobin. Finally, we show that this versatile approach is also applicable to five other organic crystalline agrochemicals, namely pinoxaden, cyproconazole, difenoconazole, isopyrazam and tebuconazole. TEM studies confirmed the adsorption of sterically stabilized nanoparticles at the surface of such agrochemical microparticles. The nanoparticles are characterized using TEM, DLS, aqueous electrophoresis and 1H NMR spectroscopy, while the final aqueous’ suspension concentrates comprising microparticles of the above six agrochemical actives are characterized using optical microscopy, laser diffraction and electron microscopy.

Stability of TMA-TEMPO-based aqueous electrolytes for redox-flow batteries

The TEMPO scaffold is one of the most prominent used posolyte systems in organic redox flow batteries (RFBs). While the aminoxyl radical is well known for his extraordinary stability, there are only a few studies investigating the stability of the respective oxoammonium cation. In this study, we utilize battery experiments to quantify the fade rate of the oxoammonium cation derived from N,N,N-2,2,6,6-heptamethylpiperidinyloxy-4-ammonium chloride (TMA-TEMPO) in correlation with temperature and time. The observed capacity decay is mostly caused by a deactivation of the oxidized TMA-TEMPO yielding the corresponding hydroxylamine, which can mostly be regenerated by reoxidation. Additionally, unbalanced compositionally symmetric flow cells are used to compare the fade rate at different temperatures combined with varying hold times showing a strong dependency on temperature and residence time in high states of charge. The acquired results are used for a use-oriented cycling program comprising a single cycle per day. Furthermore, GC-HRMS and isotopic labeling are used to analyze the volatile decomposition products of heated and oxidized TMA-TEMPO, identifying key intermediates of the decomposition mechanism and the role of an aqueous environment.

Two‐Coordinate NHC‐Supported ZnIIOrganocations: Steric and Electronic Tunability and Use in Alkyne Hydroboration Catalysis

AbstractWe herein report on the synthesis, structure, and use in alkyne hydroboration catalysis of [(IPrCl)Zn−R]+and [(ItBu)Zn−R]+cations bearing IPrCl (IPrCl=1,3‐bis[2,6‐bis(1‐methylethyl)phenyl]‐4,5‐dichloro‐1,3‐dihydro‐imidazol‐2‐ylidene) and the sterically demanding ItBu carbene (ItBu=1,3‐bis(1,1‐dimethylethyl)−1,3‐dihydro‐imidazol‐2‐ylidene). Ionization of neutral precursors [(IPrCl)ZnR2] (1 a, R=Et;1 b, R=Me) and [(ItBu)ZnEt2] (2) with one equivalent of [Ph3C][B(C6F5)4] led to with robust and stable two‐coordinate ZnIIcations [(IPrCl)Zn−R]+(3 a, R=Et;3 b, R=Me) and [(ItBu)Zn−Et]+(4), respectively, all isolated as [B(C6F5)4]−salts. Further derivatization of alkyl cations3 band4by reaction with one equivalent of [B(C6F5)3] afforded cations [(IPrCl)Zn−C6F5]+(5) and [(ItBu)Zn−C6F5]+(6) as [B(C6F5)4]−salts, with cation6displaying a limited stability in solution. The molecular structures of cations3 b,4and5were confirmed through X‐ray diffraction studies. Among stable cations, Fluoride ion affinity (FIA) estimations agree with cation5being the most Lewis acidic in thus far reported [(IPrCl)Zn−R]+cations. In the presence of pinacol borane and 1‐octyne, cations3 a–b,5and [(IPrCl)Zn−C6F5]+(5 mol%) slowly catalyze the selectivecis‐hydroboration of 1‐octyne to the vinylborane productA. Cation5also mediates 2‐hexyne hydroboration to afford a mixture of hydroboration productsBandC. In the case of hydroboration catalysis mediated by cations5and [(IPrCl)Zn−C6F5]+, experimental data and preliminary DFT calculations are consistent a Lewis‐acid‐type catalysis.

The Effect of Fluorinated Solvents on the Physicochemical Properties, Ionic Association, and Free Volume of a Prototypical Solvate Ionic Liquid.

Solvate ionic liquid (SIL) synthesis and properties depend on a delicate balancing of cation-solvent and cation-anion interactions to produce materials containing only cation-solvent complexes and solvent-separated anions. Most SILs meeting these characteristics fall within the paradigm of oligomeric ethylene oxides (e.g. glymes and glycols) and lithium salts. Targeted functionalization of solvent molecules to achieve desired properties is a relatively unexplored avenue of research. Fluorinated solvents have significantly different electric charge distributions compared to their nonfluorinated analogs. We test the impact of solvent fluorination for a SIL created from equimolar mixtures of lithium bis(trifluoromethylsulfonyl)imide (LiNTf2 ) and triethylene glycol (TEG), hereafter [(TEG)1 Li]NTf2 . In the first experiment, TEG is partially substituted with 2,2,4,4,5,5,7,7-octafluoro-3,6-dioxaoctane-1,8-diol (FTEG). This leads to a precipitous decrease in ionic conductivity and larger quantities of ionically-associated Li(NTf2 )2 - species, as detected with vibrational spectroscopy. These observations suggest FTEG does not readily coordinate Li+ ions in a manner analogous to TEG. Computational studies reinforce this conclusion. Relative complex cation stabilities are ranked as [(FTEG)1 Li]+ >[(TEG)1 Li]+ . A second experiment adds FTEG as a diluent to [(TEG)1 Li]NTf2 . This places FTEG and TEG in competition to coordinate a limited number of Li+ ions. The resulting mixtures exhibit conductivity enhancement over the parent SIL and minimal changes in ion speciation due to the poor Li+ binding by FTEG compared to TEG. Positron annihilation lifetime spectroscopic studies point to increased amounts of free volume upon dilution of FTEG. This likely explains the origin of the conductivity and viscosity enhancements.

Organometallic and Organic Dimers: Moderately Air-Stable, Yet Highly Reducing, n-Dopants.

ConspectusElectrical doping using redox-active molecules can increase the conductivity of organic semiconductors and lower charge-carrier injection and extraction barriers; it has application in devices such as organic and perovskite light-emitting diodes, organic and perovskite photovoltaic cells, field-effect transistors, and thermoelectric devices. Simple one-electron reductants that can act as n-dopants for a wide range of useful semiconductors must necessarily have low ionization energies and are, thus, highly sensitive toward ambient conditions, leading to challenges in their storage and handling. A number of approaches to this challenge have been developed, in which the highly reducing species is generated from a precursor or in which electron transfer is coupled in some way to a chemical reaction. Many of these approaches are relatively limited in applicability because of processing constraints, limited dopant strength, or the formation of side products.This Account discusses our work to develop relatively stable, yet highly reducing, n-dopants based on the dimers formed by some 19-electron organometallic complexes and by some organic radicals. These dimers are sufficiently inert that they can be briefly handled as solids in air but react with acceptors to release two electrons and to form two equivalents of stable monomeric cations, without formation of unwanted side products. We first discuss syntheses of such dimers, both previously reported and our own. We next turn to discuss their thermodynamic redox potentials, which depend on both the oxidation potential of the highly reducing odd-electron monomers and on the free energies of dissociation of the dimers; because trends in both these quantities depend on the monomer stability, they often more-or-less cancel, resulting in effective redox potentials for a number of the organometallic dimers that are approximately -2.0 V vs ferrocenium/ferrocene. However, variations in the dimer oxidation potential and the dissociation energies determine the mechanism through which a dimer reacts with a given acceptor in solution: in all cases dimer-to-acceptor electron transfer is followed by dimer cation cleavage and a subsequent second electron transfer from the neutral monomer to the acceptor, but examples with weak central bonds can also react through endergonic cleavage of the neutral dimer, followed by electron-transfer reactions between the resulting monomers and the acceptor. We, then, discuss the use of these dimers to dope a wide range of semiconductors through both vacuum and solution processing. In particular, we highlight the role of photoactivation in extending the reach of one of these dopants, enabling successful doping of a low-electron-affinity electron-transport material in an organic light-emitting diode. Finally, we suggest future directions for research using dimeric dopants.

Tuning the Electronic Properties of Main-Group Species by N-Heterocyclic Vinyl (NHV) Scaffolds

ConspectusMolecules and materials with easily tunable electronic structures and properties are at the forefront of contemporary research. π-Conjugation is fundamental in organic chemistry and plays a key role in the design of molecular materials. In this Account, we showcase the applicability of N-heterocyclic vinyl (NHV) substituents based on classical N-heterocyclic carbenes (NHCs) for tuning the structure, properties, and stability of main-group species (E) via π-conjugation and/or π-donation.NHVs such as [(NHC)═CR] (R = H or aryl) are monoanionic ligands formally derived by the deprotonation of N-heterocyclic olefins (NHOs), (NHC)═CHR. Further deprotonation of [(NHC)═CR] (R = H) is viable, giving rise to N-heterocyclic vinylidene (NHVD) species such as (NHC)═C. NHVs and NHVDs feature a highly polarizable exocyclic CNHC═C bond because of the presence of adjacent π-donor nitrogen atoms. The nature of the NHC, in particular the π-acceptor property, has a direct consequence on the polarity of the CNHC═C bond and hence on the magnitude of π-conjugation in the derived molecules. Thus, the electronic structure, especially the energy and shape of frontier molecular orbitals, HOMO and LUMO, of derived species can be fine-tuned by a judicious choice of the carbene unit. For instance, the HOMO of classical diphosphenes (RP═PR) (R = alkyl or aryl) is invariably the phosphorus lone-pair orbital, while the P═P π-bond is HOMO - 1 or HOMO - 2. In strong contrast, the HOMO of divinyldiphosphenes (R = NHV) is mainly the P═P π-bond. This is owing to the π-conjugation, resulting in the lowering of the LUMO and raising of the HOMO energy. They have a remarkably small HOMO-LUMO energy gap (4.15-4.50 eV) and readily undergo 1e-oxidations, giving rise to stable radical cations and dications.By employing a similar approach, one can access divinyldiarsenes and the corresponding radical cations and dications as crystalline solids. The use of divinyldiphosphenes and divinyldiarsenes as promising ligands in the stabilization of metalloradicals has been shown. By a logical selection of singlet carbenes, stable 2-phosha-1,3-butadiene and 2-arsa-1,3-butadiene compounds, as well as related radical cations and dications, can be prepared as crystalline solids.The relevance of NHV ligands as potent π-donors has been demonstrated for the stabilization of elusive electrophilic phosphinidene and arsinidene complexes {(NHV)E}Fe(CO)4 (E = P or As). Moreover, stable singlet diradicaloid [(NHC)CP]2 and p-quinodimethane derivatives [(NHC)CP2]2 based on an NHVD framework are accessible as stable solids.In this Account, a special emphasis is given to the contributions from this laboratory. The author hopes that this Account will serve as a useful reference guide for researchers interested in studying and applying NHV and NHVD scaffolds in modern molecular chemistry and materials sciences.

Ambipolar diarylnitroxides: Molecular design and electrochemical testing

AbstractPossible approaches to molecular design of stable diarylnitroxyl radicals capable to form sufficiently stable cations and anions under one‐electron oxidation and reduction are discussed. Both covalent and noncovalent stabilizing “tools” are considered. The main focus is made on the dynamic stabilization of oppositely charged redox states of a molecule through conformational changes. The efficiency of the approaches was confirmed on a wide range of novel diarylnitroxides designed accordingly to the suggested guidelines. Spectral and quantum‐chemical data support fast conformational changes accompanying electron transfer steps and facilitating stabilization of the cationic and anionic species. Voltammetric study of new compounds revealed the formation of reversible redox couples in both anodic and cathodic areas for the majority of nitroxides making them suitable for practical application.

Correlation between the Stability of Substituted Cobaltocenium and Molecular Descriptors.

Metallocenium cations, used as a component in an anion exchange membrane of a fuel cell, demonstrate excellent thermal and alkaline stability, which can be improved by the chemical modification of the cyclopentadienyl rings with substituent groups. In this work, the relation between the bond dissociation energy (BDE) of the cobaltocenium (CoCp2+) derivatives, used as a measure of the cation stability, and chemistry-informed descriptors obtained from the electronic structural calculations is established. The analysis of 12 molecular descriptors for 118 derivatives reveals a nonlinear dependence of the BDE on the electron donating-withdrawing character of the substituent groups coupled to the energy of the frontier molecular orbitals. A chemistry-informed feed-forward neural network trained using k-fold cross-validation over the modest data set is able to predict the BDE from the molecular descriptors with the mean absolute error of about 1 kcal/mol. The theoretical analysis suggests some promising modifications of cobaltocenium for experimental research. The results demonstrate that even for modest data sets the incorporation of the chemistry knowledge into the neural network architecture, e.g., through mindful selection and screening of the descriptors and their interactions, paves the way to gain new insight into molecular properties.

Azaborine benzylic ion stability and reactivity in ionic polymerization.

Benzylic cations and anions are implicated in the mechanism of critical organic transformations, such as styrene polymerization. We investigate the influence of BN for CC bond substitution on the reactivity of benzylic ions and the effect on BN 2-vinylnaphthalene (BN2VN) ionic polymerization. Calculations suggest that the proximity of a N donor to a cation influences the stability of a BN benzylic cation, rationalizing unsuccessful protonation of BN2VN. Organolithium reagents undergo clean nucleophilic aromatic substitution with BN2VN and related BN naphthalenes via a hypothesized associative mechanism. These results suggest design principles for main group aromatic substitution.

Chemically stable piperidinium cations for anion exchange membranes.

The chemical stability of the anion exchange membranes (AEMs) is determinative towards the engineering applications of anion exchange membrane fuel cells (AEMFCs) and other AEM-based electrochemical devices, yet remains a challenge due to deficiencies in the structural design of cations. In this work, an effective design strategy for ultra-stable piperidinium cations is presented based on the systematic investigation of the chemical stability of piperidinium in harsh alkaline media. Firstly, benzyl-substituted piperidinium was degraded by about 23% in a 7 M KOH solution at 100 °C after 1436 h, which was much more stable than pyrrolidinium due to its lower ring strain. The introduction of substituent effects at the α-C position was proved to be an effective strategy for enhancing the chemical stability of the piperidinium functional group. As a result, the butyl-substituted piperidinium cation showed no obvious structural changes after being treated in the 7 M KOH solution at 100 °C for 1050 h. Afterwards, GC-MS and NMR analysis indicated that the α-C atoms in the substituents of piperidinium are fragile to the nucleophilic attack of OH−. Based on the above results, the electronic and steric effects of different alkyl substitutions were analyzed. This work provides critical insights into the structural design of chemically stable piperidinium functional groups for the AEM and boosts its application in electrochemical devices, such as fuel cells and alkaline water electrolysis.

Excited state dynamics of a spontaneously generated TTF radical cation inside a water-soluble nanocage.

Supramolecular cavities have been traditionally used to stabilize reactive redox intermediates. Recently with the success of multiple new photoredox catalytic strategies that use supramolecular cages, there is a growing demand for photogeneration strategies of diverse reactive intermediates inside confined spaces, which will drive enzyme-like catalysis in real time. Here we report the excited state dynamics of a redox-active TTF radical cation and its corresponding dimethyl-derivative DiMeTTF inside a confined supramolecular cavity. We prepare the radical cation by spontaneous oxidation of neutral TTF upon incarceration inside a water-soluble nanocage Pd6L412+, and characterize it with a combination of resonance Raman and electron paramagnetic resonance spectroscopy. Using broadband transient absorption spectroscopy, we demonstrate that the confined native TTF radical cation and its dimethyl derivative upon photoexcitation rapidly de-excite to form the hot ground state, thereby inhibiting further oxidation to a TTF+2 dication. We discuss our results in the context of excited state crossings of the radical cation potentials as well as modifying the cage energetics to generate a stable dication. Our work has important implications for the usage of such radical cations for photoactivated catalysis.