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AKG is grateful to the Royal Society for Newton International Fellowship NF171163. We acknowledge support from the Engineering and Physical Sciences Research Council of the UK (grants EP/P010482/1 and EP/L017008/1). We are also grateful for financial support from the University of St Andrews Restarting Research and Restarting Interdisciplinary Research Funding Schemes (SARRF and SARIRF) which are funded through the Scottish Funding Council grant reference SFC/AN/08/020. We have designed a highly twisted small TADF emitter PXZ-α-DK based on an a-diketone (α-DK) as a strong acceptor and phenoxazine (PXZ) as a strong donor to obtain red-shifted emission in comparison to the equivalent a-diketone linked to 9,9-dimethyl-9,10-dihydroacridine (DMAC). The PXZ-α-DK shows emission at 586 nm and DMAC-α-DK shows emission at 548 nm in 1,3-bis(N-carbazolyl)benzene (mCP) host at 1.5 wt% doping of the emitter, with short-delayed lifetimes of 6.9 μs for PXZ-α-DK and 7.6 μs for DMAC-α-DK. OLEDs fabricated using these emitters show green electroluminescence at 555 nm for DMAC-α-DK, with a maximum external quantum efficiency, EQEmax, of 6.3%, and orange electroluminescence at 585 nm for PXZ-α-DK, with an EQEmax of 0.8%. We corroborate the optoelectronic properties of these emitters with DFT calculations. Postprint

4,4′-(4-Phenylpyridine-2,6-diyl)dibenzonitrile (PyDCN) was designed to reduce the electron-withdrawing strength and to decentralize the unsaturated N atoms relative to triazine. PyDCN was used as an acceptor to construct thermally activated delayed fluorescence (TADF) emitters PyDCN–PXZ and PyDCN–DMAC with phenoxazine (PXZ) and 9,9-dimethyl-9,10-dihydroacridine (DMAC) as electron donors. The relatively high radiative transition rate constants (kF) in the order of 107 s−1, high photoluminescence quantum yields in the range of 80–90%, and balanced charge transportation were detected for both TADF emitters. PyDCN–DMAC exhibited electroluminescence (EL) with a peak at 472 nm and CIE coordinates of (0.17, 0.26), more approaching to real blue in comparison with most of DMAC based sky-blue TADF analogues. A high external quantum yield (ηext) of 25.6% was obtained for a PyDCN–DMAC doped organic light-emitting diode (OLED). PyDCN–PXZ exhibited green EL with a ηext of 26.9% at 519 nm in the doped OLED. Its non-doped yellow OLED also revealed a moderate ηext of 18.2% with a peak at 557 nm. Furthermore, PyDCN–DMAC was used as the blue host emitter to fabricate a single-emitting-layer all-TADF white OLED in combination with a yellow home-made TADF emitter PP–PXZ, which exhibited a maximum ηext of 18.5% with CIE coordinates of (0.38, 0.44) and excellent color stability.

The study of palladium-catalyzed amination of bromobenzene with aromatic and heterocyclic amines, widely used in the synthesis of organic semiconductors, was performed. The best conditions for the coupling of aryl bromides with carbazole, diphenylamine, phenoxazine, phenothiazine, 9,9-dimethyl-9,10-dihydroacridine, and their derivatives have been developed. Based on the results, nine new star-shaped organic semiconductors, exhibiting up to 100% fluorescent quantum yield in the 400-550 nm range, have been synthesized in good yields. The TDDFT calculations of the absorption spectra revealed a good correlation with experimental results and slight solvatochromic effects with a change in the polarity of the solvent.

Three carbazole derivatives, AcPTC, PxPTC and PtPTC, consisting of two 9,9-dimethyl-9,10-dihydroacridine, phenoxazine or phenothiazine donor groups and one diphenyltriazine acceptor group fixed at 1,8,9-positions of a single carbazole ring via phenylene, are designed and synthesized. X-ray diffraction analysis of AcPTC reveals that there exist multiple π-π interactions between the donor and acceptor groups to form a sandwich-like structural unit with edge-to-face interaction model. The compounds thus show obvious thermally activated delayed fluorescence with through-space charge transfer character and possess considerable photoluminescence quantum yields of up to 73% in doped films with sky-blue to yellow emissions. The solution-processed electroluminescent devices achieve the highest maximum external quantum efficiencies of 10.0%, 11% and 5.6% for AcPTC, PxPTC and PtPTC, respectively, with small efficiency roll-offs.

Electron donating phenoxazine and phenothiazine groups were introduced in an electron deficient purine structure through a benzene ring bridge to facilitate thermally activated delayed fluorescence. Mitsunobu and Suzuki-Miyaura reactions were used to synthesize the target compounds. Photophysical properties of target compounds were explored and quantum yields in the thin layer film reached up to 8 % and in the PMMA doped thin layer film up to 15 %.

Aggregation of amyloid β42 (Aβ42) is one of the hallmarks of Alzheimer's disease (AD). The mechanism of Aβ42 aggregation mainly consists of two phases, nucleation and elongation (including plateau region as a saturation phase). During the nucleation phase, the monomer gradually forms toxic oligomers. During the elongation phase, each nucleus acts as a template and associates with monomers to initiate less toxic fibrillization. We previously proposed a method of classifying compounds into nine groups based on their ability to modulate the nucleation and/or elongation phases. An orcein derivative (O4), which is a phenoxazine dye isolated from the lichen Roccella tinctoria and containing a 2,5-cyclohexadienone moiety, was reported to convert oligomers into relatively inert fibrils, resulting in the reduction of the neurotoxicity of Aβ42. Focusing on O4 in the pursuit of anti-AD drugs, we herein screened 480 natural products including NPDepo (RIKEN) for the compounds that delayed the nucleation phase and promoted the elongation phase. The signal intensities for Aβ42 treated with each of the 15 compounds that met these criteria were lowered in dot blotting using antioligomer antibody, and the fibril formation of Aβ42 in the presence of these compounds was observed in transmission electron microscopy. Among the 15 compounds, 12 compounds (80%) reduced the toxicity of Aβ42 against mouse neuroblastoma Neuro-2a cells. Some of these anticytotoxic compounds contain 2-pyrone and 4-pyrone that interacted with Aβ42, maybe by shifting the equilibrium of Aβ from toxic oligomer into inert fibrils.

Radical cations of photoredox catalysts used in organocatalyzed atom transfer radical polymerization (O-ATRP) have been synthesized and investigated to gain insight into deactivation in O-ATRP. The stability and reactivity of these compounds were studied in two solvents, N,N-dimethylacetamide and ethyl acetate, to identify possible side reactions in O-ATRP and to investigate the ability of these radical cations to deactivate alkyl radicals. A number of other factors that could influence deactivation in O-ATRP were also probed, such as ion pairing with the radical cations, radical cation oxidation potential, and halide oxidation potential. Ultimately, these studies enabled radical cations to be employed as reagents during O-ATRP to demonstrate improvements in polymerization control with increasing radical cation concentrations. In the polymerization of acrylates, this approach enabled superior molecular weight control, a decrease in polymer dispersity from 1.90 to 1.44, and an increase in initiator efficiency from 78 to 102%. This work highlights the importance of understanding the mechanism and side reactions of O-ATRP, as well as the importance of catalyst radical cations for successful O-ATRP.

AKG is grateful to the Royal Society for Newton International Fellowship NF171163. We acknowledge support from the Engineering and Physical Sciences Research Council of the UK (grants EP/P010482/1 and EP/L017008/1). We thank the EPSRC UK National Mass Spectrometry Facility at Swansea University for analytical services. We thank Umicore for providing palladium (II) acetate. We report an organic emitter containing a β-triketone electron acceptor core and phenoxazine as the electron donors ( TPXZBM ) for solution-processed organic light-emitting diodes (OLEDs). The resulting molecule is very unusual because it shows both thermally activated delayed fluorescence (TADF) and intramolecular proton transfer. We compare its performance with the previously reported diketone analogue PXZPDO . Solution-processed OLEDs of PXZPDO and TPXZBM show maximum external quantum efficiencies of 20.1% and 12.7%, respectively. The results obtained for the solution-processed PXZPDO -based device are as good as the previously reported evaporated device. At a very high luminance of 10,000 cd/m2 the efficiency of the OLEDs was 10.6% for PXZPDO and 4.7% for TPXZBM , demonstrating relatively low efficiency roll-off for TADF materials. The low efficiency roll-off was rationalized on the basis of the short delayed lifetimes of 1.35 μs for PXZPDO and 1.44 μs for TPXZBM . Our results suggest that intramolecular proton transfer may be useful for the design of OLED materials with low efficiency roll-off. Postprint

Benzopyrylium-coumarin fluorescent probes for sensing hypochlorous acid (HClO) or sulfur dioxide (SO2) are unable to distinguish between HClO and SO2 because the two compounds can react with the 4-position of benzopyrylium-coumarin dyes through the nucleophilic attack. In the current work, we introduced a phenoxazine moiety to the benzopyrylium-coumarin dye to synthesize a new fluorescent probe PBC1, which can dually sense HClO and SO2 and generate distinct fluorescence signals with rapid response time and high sensitivity and selectivity. Moreover, probe PBC1 was also successfully utilized to detect intracellular HClO and SO2 in HeLa cells and zebrafish.

Diketopyrrolopyrrole (DPP) is one of the most used moieties in D–A conjugated polymers for high-performance π-extended conjugated polymer-based organic solar cells. The combination of 1,4-diketo-3,6-dithienylpyrrolo[3,4-c]pyrroles (DTDPPs) and the donor moieties 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenothiazine (M1), 10-(4-((2-ethylhexyl)oxy)phenyl)-10H-phenoxazine (M2), has not been reported yet. In this report, novel low-bandgap D–A conjugated polymer derivatives including DTDPP, phenothiazine and phenoxazine were successfully synthesized via direct (hetero) arylation polymerization with in the yields of 40.94–60.77%. The obtained D–A conjugated polymers named poly(3,6-Di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-alt-(10-(4-((2-ethylhexyl)oxy) phenyl)-10H-phenothiazine) (P1) and poly(3,6-Di(2-thienyl)pyrrolo[3,4-c]pyrrole-1,4-dione)-alt-(10-(4-((2-ethylhexyl)oxy) phenyl)-10H-phenoxazine) (P2) exhibited a wide range of absorption spectrum in visible light region and have a low bandgaps of 1.4–1.5 eV, as well as thermal stabilities, these D–A conjugated polymers are very promising as activated polymeric materials for organic solar cells (OSCs).

The design and synthesis of a phenoxazine-based metal-organic tetrahedron (Zn4L4) as biomimetic lectin for selectively recognition of glucosamine (GlcN) was reported. Different from the free phenoxazine-based ligand (L), Zn4L4 displayed the highest fluorescent intensity enhancement efficiency toward GlcN over other related natural mono- and disaccharides. Fluorescence titration demonstrated a 1:1 stoichiometric host-guest complex was formed with an association constant about 4.03 × 104 L/mol. 1H NMR spectroscopic studies confirmed this selectivity resulted from the multiple hydrogen bonding interactions formed between GlcN and Zn4L4. The present results suggested that rational arrangement of recognition sites in the confined space of metal-organic cage is crucial for the selectivity toward target guests.

The prediction and/or rationalization of diarylamine radical-trapping antioxidant (RTA) activity at the elevated temperatures where they are most useful presents a significant challenge, precluding the development of new technology. Whilst structure–activity relationships at ambient temperatures are well established, their predictive capacity at elevated temperatures is poor due to competing reactions. A striking example involves phenoxazine, which is a superior RTA relative to its sulfur analog phenothiazine at ambient temperature (e.g. k = 3.9 × 107vs. 7.6 × 106 M−1 s−1 at 37 °C, respectively), but is demonstrably inferior at elevated temperatures. Despite being inherently less oxidizable in electrochemical experiments and high-accuracy computations, phenoxazine is more rapidly consumed than phenothiazine in autoxidations at 160 °C – a result which we attribute to a lower reorganization energy barrier to oxidation. Given these observations, we surmised that incorporation of an electronegative N-atom into the phenoxazine ring system would decrease the driving force for oxidation and ‘rescue’ its activity. Indeed, this was found to be the case for nitrogen incorporation at any position, regardless of the impact on the inherent RTA activity. Analogous experiments were carried out on phenothiazines into which nitrogen atoms were incorporated, revealing little benefit at 160 °C. These results suggest that for highly reactive diarylamines (i.e. those with k > 106 M−1 s−1), further enhancements in reactivity do not materially improve their ability to inhibit hydrocarbon autoxidation at elevated temperatures. Instead, their stability to one-electron oxidation determines their efficacy., Studies of potent diarylamine antioxidants illustrate how their high-temperature activity can be limited by direct reaction with O2, and how driving force and barrier to oxidation can be modulated for future antioxidant development.

It is a pre-requisite to ionize analyte molecules efficiently for detection by laser desorption/ionization mass spectrometry. Here, we report a conceptual demonstration of cationizing neutral small molecules which are typically difficult to be ionized with the traditional organic matrices due to their low proton/cation affinity values. Our strategy features generating radical cations from site-specifically carboxylated 10-(4-carboxyphenyl)-10H-phenothiazine-3,7-dicarboxylic acid (PTZ(A)2-Ph(A)) with a laser, and anchoring the chlorine ion from NaCl through covalent bond-like bridging interactions with the N/S atoms in the heterocyclic structure. This “Maverick” design allows a dramatic change of the energy landscape of analyte sodiation with an enhanced efficiency. We have synthesized two families of compounds based on the model structures of phenothiazine (PTZ) and phenoxazine (PXZ) and their carboxylated derivatives, and performed comparison between them or against the traditional organic matrices in a systematic format. We have demonstrated that PTZ(A)2-Ph(A) is outstanding as a novel MALDI matrix for the detection of oligosaccharides and amino acids, with an ultra-clean background baseline and high signal-to-noise ratios (up to dozens of times better than the traditional matrices). This work provides a new method for the cationization of neutral small molecules in a distinct mechanism, inspiring the development of next-generation matrices for sensitive detection of hard-to-be-ionized molecules by MALDI MS.

Quorum sensing inhibitors (QSIs) can block the quorum sensing system and might be useful in therapy of drug-resistant bacterial infections. To explore the anti-quorum sensing actinomycetes from marine habitats, in this study, a marine actinobacterium exhibiting strong anti-quorum sensing activity was isolated from marine sediment and identified as Nocardiopsis dassonvillei JS106. Effects of different culture media on the bioactivity and metabolites production of JS106 were investigated by using single-factor and orthogonal experiments. The results showed that soybean meal and NaCl were two important factors in the culture medium, and could significantly affect both the bioactivity and metabolites production of JS106. By culturing in the optimized medium containing 10 g/L soluble starch, 10 g/L soybean meal, and 15 g/L NaCl at pH 6.5, both metabolites production and anti-quorum sensing activity of JS106 were significantly increased (302 and 241%, respectively) compared to the original condition. The culture liquid of JS106 also showed strong anti-biofilm activity against Staphylococcus aureus and Pseudomonas aeruginosa with the inhibition rate of 77.94 and 50.56% at the concentration of 20 vol %, while it did not inhibit the growth of planktonic cells. Questiomycin A and a new compound 2-hydroxyacetate-3-hydroxyacetamido-phenoxazine (HHP) were isolated and identified from the cultures of JS106. The anti-quorum sensing activities (IC50) of questiomycin A and HHP against violacein production by Chromobacterium violaceum 12472 were 6.82 and 23.59 μg/mL, respectively. The strong anti-quorum sensing activity of N. dassonvillei JS106 indicated that this strain and its active phenoxazine metabolites could have good potential in anti-quorum sensing related applications.

Phenothiazine dyes have attracted significant attention as metal-free sensitizers for dye-sensitized solar cells since their introduction in 2007. Since then, over 430 phenothiazine dyes have been prepared and investigated. Despite the ever-increasing molecular variation, the overall improvement in the power conversion efficiency has been slow. In this review, we identify the traits of successful phenothiazine dyes and shed light on inherent molecular limitations. We include all phenothiazine dyes reported to date, and the big dataset is used to look for trends in photophysical, electrochemical and photovoltaic performance. The dataset used in this study is curated to contain only photovoltaic performance data that is validated using a novel credibility assessment. We compare the distinct sub-geometries of phenothiazine dyes, and investigate the effects of auxiliary donors, the use of π-spacers, DSSC electrolyte compatibility, N-alkyl vs. N-aryl substituents and mono- vs. multianchored vs. tethered dyes. Lastly, the phenothiazine dyes are compared to their closest dye analogue, the phenoxazines. Based on the findings in this review, we believe phenothiazine dyes are unlikely to be the main sensitizers of high-efficiency DSSCs in the future, due to low oxidation potentials, low extinction coefficients and inherent limitations restricting the further optimization of their photophysical properties.

The lack of high throughput screening (HTS) techniques for small molecules that stabilize DNA iMs limits their development as perspective drug candidates. Here we showed that fluorescence monitoring for probing the effects of ligands on the iM stability using the FAM-BHQ1 pair provides incorrect results due to additional dye-related interactions. We developed an alternative system with fluorescent phenoxazine pseudonucleotides in loops that do not alter iM unfolding. At the same time, the fluorescence of phenoxazine residues is sensitive to iM unfolding that enables accurate evaluation of ligand-induced changes of iM stability. Our results provide the basis for new approaches for HTS of iM ligands.

Redox-active covalent organic frameworks (COFs) with dense redox sites are promising electrical energy storage materials with robust architectures, high surface areas, insolubility in electrolytes, and open pores for electrolyte transportation. However, low redox potentials and poor electrical conductivity of pristine COFs often result in low accessibilities of redox-active sites and slow redox kinetics, greatly limiting their practical applications. Herein, we report the design and synthesis of two novel p-type phenoxazine-based COFs (DAPO-COFs) with high redox potentials (∼3.6 V vs. Li/Li+) and excellent electrical conductivities. Simply blended with conductive additives (CAs) and binders, pristine bulk DAPO-COFs without pre-composition with CAs or extra exfoliation are readily useable as cathode materials for lithium-ion batteries. Both as-synthesized DAPO-COF powders displayed superior active-site accessibility, ultrafast redox kinetics, and remarkable cycling stability. This work provides new perspectives on the development of readily useable COF-based cathode materials, and contributes to the advancement of eco-friendly and sustainable organic-based energy storage devices.

A new copper(II) complex (I) was obtained by the reaction of a sterically crowded 2,4-di-(tert-butyl)-9-chloro-benzo[5,6][1,4]oxazine[2,3-b]phenoxazine bridging ligand with Cu(II) hexafluoroacetylacetonate. Compound I is a quasi-one-dimensional complex in which the Cu(hfac)2 moieties are co-crystallized with the triphenodioxazine molecules through only weak Cu⋯N short intermolecular interactions (the Cu⋯N distances are 2.732 and 2.752 A). The magnetic AC susceptibility data show that in spite of the absence of zero-field splitting in the Cu(II) ion with S = 1/2, the compound demonstrates a slow magnetic relaxation behaviour at a weak applied magnetic field (HDC = 500 Oe). The EPR spectra and DC magnetic measurements show the strong axial anisotropy of the g-tensor. The temperature dependence of the relaxation time is well described by the combination of one-phonon direct and two-phonon Raman processes.

Developing highly efficient red thermally activated delayed fluorescence (TADF) emitters remains a formidable challenge due to strict molecular design principles. In this contribution, two red emitters PXZ-AQPy and PXZ-AQPhPy with high structural rigidity and linear configurations are designed and synthesized based on phenoxazine (PXZ) as a donor and acenaphtho[1,2-b]quinoxaline (AQ) as an acceptor. Both molecules with horizontal orientation are endowed with TADF and aggregation-induced emission (AIE) properties. By elongating the acceptor segment via phenyl decoration, PXZ-AQPhPy exhibits higher horizontal ratios of the emitting dipole orientation (Θ‖ = 85%), while the emission characteristics are almost unaltered. Consequently, the PXZ-AQPhPy based device achieves a high external quantum efficiency of 19.6% with an emission peak at 610 nm. This work provides a simple and effective design strategy to selectively promote the horizontal orientation of red TADF emitters.

Developing organic dyes with di-/multi-anchors has aroused increasing attention in recent years due to these dyes had many advantages in comparison with the analogues of single acceptor. Herein, four (D–π–A)-L2-(A–π–D–π–A)2 dyes (TQ1−2, OQ1−2) along with a reference D−(π–A)2 dye (TD), comprising phenothiazine/phenoxazine as a donor, thiophene as a π space, cyanoacetic acid as an acceptor and saturated n-hexyl/n-dodecyl as a flexible linker have been prepared and characterized. The correlative between the variation of structure and the optical, electrochemical properties in addition to photovoltaic performances of the dyes have been explored. Besides, the ultraviolet–visible spectra in solution and on the TiO2 film, cyclic voltammetry, photocurrent-voltage scan, incident photon-to-current conversion efficiency and electrochemical impedance spectroscopic of the presented dyes have been investigated. Compared with the reference dye TD, TQ1−2 and OQ1−2 exhibit higher molar extinction coefficient, broader and stronger incident photon-to-current conversion efficiency response spectrum, and higher density of light-absorbing units adsorbed on the TiO2 surface. Among the cells based on the pristine dyes, the relatively high photocurrent of OQ1-2 by comparison with the counterparts of TQ1−2 is attributed to the incorporation of phenoxazine donor into the (A–π–D–π–A)2 units. An increase open-circuit voltage of TQ2 and OQ2 compared to TQ1 and OQ1 is ascribed to the higher charge recombination resistance and the longer electron lifetime in their cells. Consequently, a maximum power conversion efficiency of 6.77% is attained by the TQ2-based cells with iodide/triiodide electrolyte under the illumination of 100 mW cm−2.

An organic reaction in water using visible light as the only energy source is one of the goals of modern synthetic organic chemistry, and the encapsulation of a photoredox catalyst by a water-solub...

Research and development of new organic semiconductor materials can never be terminated because any structural fine-tuning may result in an important impact on its application performance, although the effect may be negative in many cases. Herein, we designed and synthesized a series of phenoxazine-based dyes, YH1, YH2, YH3, and YH4, whose absorption spectrum, electrochemical cyclic voltammetry, theoretical calculation, dye-sensitized solar cell photovoltaic characteristics, and electrochemical AC impedance are used to analyze the photophysical, electrochemical, and photovoltaic performance of the materials, aiming to study the effect of multidonor and adjustment of the chromophore insertion position on their photovoltaic performance. When donor triphenylamine is added at the end of YH1 and YH3, the absorption spectrum and photovoltaic performance of dyes YH2 and YH4 improved a little. The improvement is much greater when the chromophore (ethylenedioxy)thiophene in YH1 and YH2 is adjusted and inserted on the other side of phenoxazine and the energy conversion efficiencies (photon-to-current conversion efficiency) of the resulting dyes YH3 and YH4 reach 8.02 and 8.97%, respectively, which are 23 and 25% higher than those of YH1 and YH2, respectively. Although the improvement may be because of factors such as the dihedral angle, the result will undoubtedly provide some reference for the future study of the relationship between the structure and performance of organic dyes.

A condensed phenoxazine dimer was synthesized and characterized. X-ray crystallographic analysis of the dimer shows a double-butterfly structure, in which the nitrogen atoms are located above and below the molecular plane. A radical cation salt of the dimer was obtained using tris(4-bromophenyl)aminium hexafluoroantimonate as the oxidant. The salt is air-stable in solid and solution states. The cation structure was evaluated by X-ray crystallographic analysis, showing that the phenoxazine units were converted to a planar structure upon oxidation.

It is well known that copper ions play a critical role in various physiological processes. However, a variety of human diseases are tightly correlated with copper overload. Although there are numerous fluorescent probes capable of detecting copper ions, most of them are "turn-off" probes owing to copper (II) ions fluorescence quenching effect, resulting in poor sensitivity. Herein, a novel "turn-on" near-infrared (NIR) fluorescent probe PZ-N based on phenoxazine was designed and synthesized for the selective detection of copper (II) ions (Cu2+ ). Upon the addition of Cu2+ , the probe could quickly react with Cu2+ and emit strong fluorescence, along with colour change from colourless to obvious blue. Moreover, the probe PZ-N showed good water solubility, high selectivity, and excellent sensitivity with low limit of detection (1.93 nM) towards copper (II) ions. More importantly, PZ-N was capable of effectively detecting Cu2+ in living cells.

Pendant sulfone/phenoxazine-based homo- and copolymers were synthesized via the radical (co)polymerization of 4-bromophenyl vinyl sulfide (BPVS) and styrene (St) followed by oxidation of the thus-p...

Organic photocatalytic atom transfer radical polymerization (ATRP) has recently become a research highlight. Organic photocatalysts based on phenothiazine, phenoxazine, and phenazine have been reported and exhibited remarkable performance. All of those structures contain two heteroatoms, which makes the oxidative state (i.e., the radical cation) of the photocatalysts stable enough to complete the catalytic cycle. However, despite the similar structure, 9,9-dimethyl dihydroacridine (DHA) was rarely used for constructing photocatalyst due to its unstable oxidative state. DHA is a weak electron donor that was widely applied in blue-emitting thermally activated delayed fluorescence (TADF) molecules. Its weaker electron-donating ability will contribute to a higher energy level of the excited state. Also, the higher oxidation potential of its radical cation will contribute to better controllability due to fast reversible dormancy. In this study, we found that substitution on the active sites of DHA could make it stable enough to be the donor part of a donor–acceptor (D–A)-type photocatalyst for ATRP. Moreover, chemical modification is necessary for both stabilizing the radical cation and improving the controllability in the polymerization process. Further modification was made to construct a rapid equilibrium between initiation and reversible dormancy, and polymerization with quantitative initiator efficiencies was achieved with a polydispersity of 1.14. It is notable that such modification can probably apply to different kinds of electron donors, and various organic chromophores could thus be applied to construct organic photocatalyst with superior performance.

Nitroxides were recently shown to catalyze the cross-dismutation of alkylperoxyl and hydroperoxyl radicals, making them uniquely effective radical-trapping antioxidants (RTAs) in unsaturated hydrocarbons where both species are formed. Given the abundance of unsaturated lipids in biological membranes, the continuous generation of hydroperoxyl (superoxide) as a byproduct of aerobic respiration, and the demonstrated cytoprotective properties of some nitroxides, we probed if cross-dismutation operates in phospholipid bilayers and cell culture. Interestingly, only nitroxides that were efficiently converted to amines in situ were effective, with their activity paralleling the stability of the incipient aminyl radicals. The ether-linked diarylamine phenoxazine, one of the most potent RTAs known, was particularly effective as a cross-dismutation catalyst. In contrast, phenolic RTAs such as α-tocopherol (α-TOH), the most potent form of vitamin E, were found to be inefficient due to the preference for the combination of hydroperoxyl and phenoxyl radicals over H-atom transfer between them. Experiments carried out in mouse embryonic fibroblasts corroborated these findings. Cells cotreated with phenoxazine (or its nitroxide) and a superoxide source were better protected from ferroptosis than those treated with phenoxazine (or its nitroxide) alone. No such synergy was observed for cells treated with α-TOH. Live cell imaging established that cytoprotection was associated with suppression of (phospho)lipid peroxidation. These results highlight the remarkable capacity for select amines to act as effective phase-transfer catalysts for a reducing equivalent (an H atom), such that a water-soluble "reactive oxygen species" can be used to quench a lipid-soluble one.

We report here the rational architecture of heteroanthracene-based metal-free organic D−π–A sensitizers (DS-1 and DS-2) and solid organic redox shuttles (ORSs) with common donor moieties phenothiaz...

We study the effect of molecular conformation on the electronic coupling between the donor amines and acceptor 1,8-naphthalimide (NPI) in a series of D-A systems 1-4 (A = NPI; D = phenothiazine, phenoxazine, carbazole, diphenylamine, respectively, for 1, 2, 3, and 4). Weakly coupled systems show dual emission in the solution state, while strongly coupled systems show single emission bands. The energy of transitions and photoluminescence (PL) quantum yield are sensitive to the molecular conformation and donor strength. These compounds show delayed emission in the solutions and aggregated state and phosphorescence in the solid state. Compounds 3 and 4 with weak donors exhibit intermolecular slipped π···π interactions in the solid state and consequently exhibit dual (intra- and inter-) phosphorescence at low temperature. Steady state and time-resolved PL studies at variable temperature together with computational and crystal structure analysis were used to rationalize the optical properties of these compounds. The delayed emission of these compounds is sensitive to molecular oxygen; accordingly, these molecules are utilized for differential imaging of normoxia and hypoxia cancer cells.

Structurally robust tetradentate gold(III)-emitters have potent material applications but are rare and unprecedented for those displaying thermally activated delayed fluorescence (TADF). Herein, a novel synthetic route leading to the preparation of highly emissive, charge-neutral tetradentate [C^C^N^C] gold(III) complexes with 5-5-6-membered chelate rings has been developed through microwave-assisted C-H bond activation. These complexes show high thermal stability and with emission origin (3 IL, 3 ILCT, and TADF) tuned by varying the substituents of the C^C^N^C ligand. With phenoxazine/diphenylamine substituent, we prepared the first tetradentate gold(III) complexes that are TADF emitters with emission quantum yields of up to 94 % and emission lifetimes of down to 0.62 μs in deoxygenated toluene. These tetradentate AuIII TADF emitters showed good performance in vacuum-deposited OLEDs with maximum EQEs of up to 25 % and LT95 of up to 5280 h at 100 cd m-2 .

Thermally activated delayed fluorescence (TADF) materials, combining high fluorescence quantum efficiency and short delayed emission lifetime, are highly desirable for application in organic light-emitting diodes (OLEDs) with negligible external quantum efficiency (EQE) roll-off. Here, we present the pathway for shortening the TADF lifetime of highly emissive 4,6-bis[4-(10-phenoxazinyl)phenyl]pyrimidine derivatives. Tiny manipulation of the molecular structure with methyl groups was applied to tune the singlet–triplet energy-level scheme and the corresponding coupling strengths, enabling the boost of the reverse intersystem crossing (rISC) rate (from 0.7 to 6.5) × 106 s–1 and shorten the TADF lifetime down to only 800 ns in toluene solutions. An almost identical TADF lifetime of roughly 860 ns was attained also in solid films for the compound with the most rapid TADF decay in toluene despite the presence of inevitable conformational disorder. Concomitantly, the boost of fluorescence quantum efficiency to near unity was achieved in solid films due to the weakened nonradiative decay. Exceptional EQE peak values of 26.3–29.1% together with adjustable emission wavelength in the range of 502–536 nm were achieved in TADF OLEDs. Reduction of EQE roll-off was demonstrated by lowering the TADF lifetime.

Phenoxazine derivatives such as Nile Blue analogues are assumed to be increasingly relevant in cell biology due to their fluorescence staining capabilities and antifungal and anticancer activities. However, the mechanisms underlying their effects remain poorly elucidated. Using S. cerevisiae as a eukaryotic model, we found that BaP1, a novel 5- and 9-N-substituted benzo[a]phenoxazine synthesized in our laboratory, when used in low concentrations, accumulates and stains the vacuolar membrane and the endoplasmic reticulum. In contrast, at higher concentrations, BaP1 stains lipid droplets and induces a regulated cell death process mediated by vacuolar membrane permeabilization. BaP1 also induced mitochondrial fragmentation and depolarization but did not lead to ROS accumulation, changes in intracellular Ca2+, or loss of plasma membrane integrity. Additionally, our results show that the cell death process is dependent on the vacuolar protease Pep4p and that the vacuole permeabilization results in its translocation from the vacuole to the cytosol. In addition, although nucleic acids are commonly described as targets of benzo[a]phenoxazines, we did not find any alterations at the DNA level. Our observations highlight BaP1 as a promising molecule for pharmacological application, using vacuole membrane permeabilization as a targeted approach., Joao C. C. Ferreira (SFRH/BD/133207/2017) acknowledges a doctoral grant (from the Fundacao para a Ciencia e Tecnologia) FCT. This work was supported by the strategic programs UIDB/04050/2020, UID/QUI/0686/2016 and UID/QUI/0686/2019 funded by national funds through the FCT I.P. Thanks are due to FCT for financial support to the Portuguese NMR network (PTNMR), Bruker Avance III 400-Univ. Minho. This work was also funded by FCT within the scope of the project PTDC/QUIQIN/28662/2017.

The synthesis of phenoxazine dyes was revisited in order to access these fluorescent N,O-heterocycles under mild conditions. The combined sequential use of nitrosonium tetrafluoroborate (NOBF4) and triphenylphosphine enables the facile conversion of bis(3-dimethylaminophenyl) ether into the methyl analog of popular laser dye oxazine 1. The ability of nitrosonium cation (NO+) to initiate the domino reaction resulting in pi-conjugated phenoxazine molecules under neutral conditions, then led us to explore the feasibility of expanding it in aqueous media. Thus, we explored the use of reactive signaling molecule nitric oxide (NO) as a biological trigger of phenoxazine synthesis in water. The implementation of a robust analytical methodology based on fluorescence assays and HPLC-fluorescence/-MS analyses, have enabled us to demonstrate the viability of this novel fluorogenic reaction-based process to selectively yield an intense "OFF-ON" response in the near-infrared (NIR-I) spectral region. This study is an important step towards the popularization of the concept of "covalent-assembly" in the fields of optical sensing, bioimaging and molecular theranostics.

C28H23N3O3, orthorhombic, Pna21 (no. 33), a = 29.0466(11) Å, b = 5.2448(3) Å, c = 14.4825(7) Å, V = 2206.32(19) Å3, Z = 4, R gt (F) = 0.0511, wR ref (F 2) = 0.1341, T = 100.00(10) K.

A facile and efficient quinoline-fused 4H-benzo[b][1,4]oxazine has been successfully fabricated through an oxidative O-arylation, Pd-catalyzed double N-arylation of 4-hydroxyquinoline derivatives and trivalent aryl iodides. Diversified fused heterocycles could be easily constructed in overall high isolated yields with great substrate scope. The afforded heteroatom-"doped" phenoxazine 3 demonstrated high molar absorptivities and excellent stability and redox reversibility. These phenoxazine analogues therefore could be utilized as promising catalysts in the photoredox catalyzed perfluoroalkylation of heteroarenes and photopromoted radical polymerization (OATRP).

The therapeutic repertoire for tuberculosis (TB) remains limited despite the existence of many TB drugs that are highly active in in vitro models and possess clinical utility. Underlying the lack of efficacy in vivo is the inability of TB drugs to penetrate microenvironments inhabited by the causative agent, Mycobacterium tuberculosis, including host alveolar macrophages. Here, we determined the ability of the phenoxazine PhX1 previously shown to be active against M. tuberculosis in vitro to differentially penetrate murine compartments, including plasma, epithelial lining fluid, and isolated epithelial lining fluid cells. We also investigated the extent of permeation into uninfected and M. tuberculosis-infected human macrophage-like Tamm-Horsfall protein 1 (THP-1) cells directly and by comparing to results obtained in vitro in synergy assays. Our data indicate that PhX1 (4,750 ± 127.2 ng/ml) penetrates more effectively into THP-1 cells than do the clinically used anti-TB agents, rifampin (3,050 ± 62.9 ng/ml), moxifloxacin (3,374 ± 48.7 ng/ml), bedaquiline (4,410 ± 190.9 ng/ml), and linezolid (770 ± 14.1 ng/ml). Compound efficacy in infected cells correlated with intracellular accumulation, reinforcing the perceived importance of intracellular penetration as a key drug property. Moreover, we detected synergies deriving from redox-stimulatory combinations of PhX1 or clofazimine with the novel prenylated amino-artemisinin WHN296. Finally, we used compound synergies to elucidate the relationship between compound intracellular accumulation and efficacy, with PhX1/WHN296 synergy levels shown to predict drug efficacy. Collectively, our data support the utility of the applied assays in identifying in vitro active compounds with the potential for clinical development. IMPORTANCE This study addresses the development of novel therapeutic compounds for the eventual treatment of drug-resistant tuberculosis. Tuberculosis continues to progress, with cases of Mycobacterium tuberculosis (M. tuberculosis) resistance to first-line medications increasing. We assess new combinations of drugs with both oxidant and redox properties coupled with a third partner drug, with the focus here being on the potentiation of M. tuberculosis-active combinations of compounds in the intracellular macrophage environment. Thus, we determined the ability of the phenoxazine PhX1, previously shown to be active against M. tuberculosis in vitro, to differentially penetrate murine compartments, including plasma, epithelial lining fluid, and isolated epithelial lining fluid cells. In addition, the extent of permeation into human macrophage-like THP-1 cells and H37Rv-infected THP-1 cells was measured via mass spectrometry and compared to in vitro two-dimensional synergy and subsequent intracellular efficacy. Collectively, our data indicate that development of new drugs will be facilitated using the methods described herein.

application/pdf, The Journal of Physical Chemistry. 2021, 12 (38), P.9283-9292

Emerging and re-emerging viruses periodically cause outbreaks and epidemics all over the world, eventually leading to global events such as the current pandemic of the novel SARS-CoV-2 coronavirus infection COVID-19. Therefore, an urgent need for novel antivirals is crystal clear. Here we present the synthesis and evaluation of an antiviral activity of phenoxazine-based nucleoside analogs divided into three groups: (1) 8-alkoxy-substituted, (2) acyclic, and (3) carbocyclic. The antiviral activity was assessed against a structurally and phylogenetically diverse panel of RNA and DNA viruses from 25 species. Four compounds (11a-c, 12c) inhibited 4 DNA/RNA viruses with EC50 ≤ 20 μM. Toxicity of the compounds for the cell lines used for virus cultivation was negligible in most cases. In addition, previously reported and newly synthesized phenoxazine derivatives were evaluated against SARS-CoV-2, and some of them showed promising inhibition of reproduction with EC50 values in low micromolar range, although accompanied by commensurate cytotoxicity., Graphical abstract Image 1

Although organic p-type cathode materials with high redox potential (>3.5 V vs. Li/Li+) are sustainable alternatives to transition metal oxide cathodes for lithium-ion batteries, only a limited number of these materials have been investigated to date. Therefore, the discovery of new p-type redox centers is essential for further development of successful organic cathodes. Herein, we report phenoxazine (PXZ) as a new p-type redox center for high-voltage cathode materials. Negligible structural reorganization of this PXZ center facilitates a kinetically faster electrochemical pathway, leading to a narrow voltage plateau, full utilization of the capacity, and superior rate capability in a new PXZ-based cathode material, PXZ trimer (3PXZ). The 3PXZ cathode delivered a specific capacity of 112 mA h g−1 at 1C with a high average discharge voltage of 3.7 V vs. Li/Li+ in a Li-organic cell; moreover, even at a high rate of 20C, 73% capacity retention (76 mA h g−1) was achieved. In addition, a 3PXZ composite with mesoporous carbon CMK-3 exhibited a capacity of 100 mA h g−1 with high stability, losing only 0.044% capacity per cycle over 500 cycles at 5C. As 3PXZ outperforms most reported p-type cathodes in terms of both rate capability and stability, we suggest the adoption of the PXZ unit as a novel and promising redox center for high-performance and sustainable energy storage systems.

Endowing thermally activated delayed fluorescence (TADF) emitters with aggregation-induced emission (AIE) characteristics and a fine film-forming ability is significant for realizing efficient solution-processed non-doped organic light-emitting diodes (OLEDs). Herein, a class of AIE-active TADF emitters adopting phenyl ketone as an acceptor and 9,9-diphenyl-9,10-dihydroacridine (or 9,9-dimethyl-9,10-dihydroacridine and phenoxazine) as a donor are exploited. The suppressed intermolecular packing derived from the highly twisted molecular configuration and multiple transition channels induce improved luminescence efficiency and more efficient reverse intersystem crossing (RISC) simultaneously in the solid state. Solution-processed non-doped and doped devices with the maximum external quantum efficiencies (EQEs) of 12.1% and 17.6%, respectively, are obtained when employing the dendritic luminogens of 3PXZ-BPCTPA as the emitter, which are better than the reference non-dendritic luminogens of PXZ-BPCTPA. This work thus provides an approach for designing dendritic luminogens with TADF and AIE features as promising candidates for high-performance solution-processed OLEDs.

N-Borylated emitters bearing both boron dimesityl acceptor (Mes)2B and phenoxazine or acridine donors are a class of efficient TADF emitters; however, switching to a carbazole donor nullifies the TADF characteristics. This work is targeted at improving the TADF characteristics of the carbazole based (Mes)2B emitters by introducing up to two methoxy substituents at the carbazoles. We hereby report the design and synthesis of three methoxy substituted carbazoles (Cz-1, Cz-2 and Cz-3) and the corresponding directly N-borylated emitters, CzBM-1, CzBM-2 and CzBM-3. Moreover, a p-phenylene spacer was also introduced between the (Mes)2B unit and carbazole, giving CzPBM-2 and CzPBM-3. As confirmed by the bi-exponential transient decay analyses, all title compounds exhibit prominent TADF character, while the parent molecules CzBM-0 and CzPBM-0 without methoxy groups show no TADF characteristics. The results manifest the importance of the donor strength of substituents and degrees of spatial orthogonality in harnessing the charge transfer properties, minimalizing the S1–T1 energy gap and facilitating the reverse intersystem crossing process. OLED devices with doped CzBM-2 and CzPBM-3 emitters exhibited a maximum external quantum efficiency of 12.5% and 13.3%, respectively, confirming the potential of methoxy substituents in improving their TADF characteristics.