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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.

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.

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.

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.

Understanding and control of weak intermolecular interactions, including π-interactions, is an element toward the strategic design of supramolecular materials. In this work, we describe an approach...

The spin–orbit charge-transfer-induced intersystem crossing (SOCT-ISC) in Bodipy-phenoxazine (BDP-PXZ) compact electron-donor/-acceptor dyads was studied. PXZ is the electron donor, and BDP is the ...

A phenoxazine-based fluorescence chemosensor 4PB [(4-(tert-butyl)-N-(4-((4-((5-oxo-5H-benzo[a]phenoxazin-6-yl)amino)phenyl)sulfonyl)phenyl)benzamide)] was designed and synthesized by a simple synthetic methods. The 4PB fluorescence chemosensor selectively detects Ba2+ in the existence of other alkaline metal ions. In addition, 4PB showed high selectivity and sensitivity for Ba2+ detection. The detection limit of 4PB was 0.282 μM and the binding constant was 1.0 × 106 M-1 in CH3CN/H2O (97.5:2.5 v/v, HEPES = 1.25 mM, pH 7.3) medium. This chemosensor functioned through the intramolecular charge transfer (ICT) mechanism, which was further confirmed by DFT studies. Live cell imaging in MCF-7 cells confirmed the cell permeability of 4PB and its capability for specific detection of Ba2+ in living cells.

In the colorful world of pigments and dyes, the chemical reduction of chromophores usually leads to bleaching because of π-conjugation interruption. Yet, the natural phenoxazinone-based ommochrome pigment called xanthommatin displays a bathochromic (i.e. red) shift upon two-electron reduction to its corresponding phenoxazine, whose electronic origins are not completely disclosed. In this study, we investigated, at quantum chemical level, a series of phenoxazinone/phenoxazine pairs that was previously explored by UV-Vis spectroscopy (Schäfer and Geyer, 1972), and which displays different hypsochromic and bathochromic shifts upon reduction. Density Functional Theory (DFT) and Time-Dependent DFT (TDDFT) have been applied to compute their optical properties in order to find a rational explanation of the observed photophysical behavior. Based on our results, we propose that the electro-accepting power of auxochromes and their conjugation facilitate intramolecular charge-transfers across the phenoxazine bridge by lowering unoccupied molecular orbitals via electronic and geometric couplings, leading ultimately to bathochromy. Our findings therefore suggest new potential ways to adjust the color-changing ability of phenoxazinones in technological contexts. Overall, this model extends our mechanistic understanding of the many biological functions of ommochromes in invertebrates, from tunable color changes to antiradical behaviors.

In this study, we showed the distortion of the central axis of the donor moiety can switch critically the rate of the reverse intersystem crossing (kRISC) process, which is the trigger point to modulate the lifetime of delayed fluorescence. To achieve kRISC, what we desired (105 to 106 s–1) in a series of donor–acceptor–donor (D–A–D) type thermally activated delayed fluorescence (TADF) materials, the donor groups (phenoxazine and phenothiazine) were selectively introduced. Maintaining the near orthogonality between donor and acceptor (benzonitrile) moiety, the occurrence of the distortion of the central axis of the donor moiety could make the effect of locally excited triplet state (3LE). In other words, the interaction between 3LE and the charge transfer counterparts (i.e., 1CT and 3CT) contributes an opposite propensity of kRISC for each of the target TADF materials when those are dissolved in solution and condensed in solid state. Herein, we have theoretically and experimentally shown the photophysical...

Two novel simple-constructed and low-cost hole transport materials (HTMs) POZ9 and POZ10, incorporating a phenoxazine (POZ) core unit, were designed and synthesized for application in perovskite solar cells (PSCs). The typically semblable molecular structure of POZ9 and POZ10 cause them to possess similar energy levels. However, their photovoltaic performances are quite different from each other because of the small variations of N-substitution on POZ ring. The PSCs based on POZ10, which contains three N, N-di-4-methoxyphenylamino units, achieved a power conversion efficiency (PCE) of 19.4%, while the PSC adopting POZ9 as HTM obtained a lower PCE of 17.1%. Moreover, the light intensity dependence research showed that POZ10 has a better hole transporting ability and can efficiently resist the charge recombination.

Achieving red phosphorescence from purely organic system is a challenging feat due to the predominant thermal nonradiative decay pathways of the excited electrons. Here, we design single-component ...

Melanoma is a type of highly malignant and metastatic skin cancer, and early detection of melanoma by analyzing the level of its biomarker may decrease the likelihood of mortality. In this study, a fluorescent probe called NBR-AP for detecting tyrosinase (a biomarker of melanoma) has been created by incorporating a hydroxyphenylurea group (as a substrate for the enzyme) onto a fluorescent dye phenoxazine derivative (as an activatable signal reporter). This probe can be activated to generate fluorescence through a tyrosinase-mediated oxidation followed by hydrolysis of the urea linkage. The probe is able to detect the endogenous tyrosinase level in live cells and in zebrafish sensitively and selectively. Moreover, by imaging the tyrosinase activity, NBR-AP has been successfully applied to diagnose the melanoma and its metastasis in xenogeneic mouse models established via subcutaneous injection of B16F10 cells.

We report the unprecedented dual properties of excited-state structural planarization and thermally activated delayed fluorescence (TADF) of 10-dimesitylboryl phenoxazine, i.e., PXZBM. Bearing a nonplanar phenoxazine moiety, PXZBM shows the lowest lying absorption onset at ∼390 nm in nonpolar solvents such as cyclohexane but reveals an anomalously large Stokes-shifted (∼14 500 cm–1) emission maximized at 595 nm. In sharp contrast, when a phenylene spacer is added between phenoxazine and dimesitylboryl moieties of PXZBM, the 10-(4-dimesitylborylphenyl)phenoxazine PXZPBM in cyclohexane reveals a much blue-shifted emission at 470 nm despite its red-shifted absorption maximized at 420 nm (cf. PXZBM). The emission of PXZBM further reveals solvent polarity dependence, being red-shifted from 595 nm in cyclohexane to 645 nm in CH2Cl2. For rationalization, the steric hindrance between phenoxazine and the dimesitylboryl unit in PXZBM caused a puckered arrangement of phenoxazine at the ground state. Upon electronic ...

Through the study of structure-property relationships using a combination of experimental and computational analyses, a number of phenoxazine derivatives have been developed as visible light absorbing, organic photoredox catalysts (PCs) with excited state reduction potentials rivaling those of highly reducing transition metal PCs. Time-dependent density functional theory (TD-DFT) computational modeling of the photoexcitation of N-aryl and core modified phenoxazines guided the design of PCs with absorption profiles in the visible regime. In accordance with our previous work with N, N-diaryl dihydrophenazines, characterization of noncore modified N-aryl phenoxazines in the excited state demonstrated that the nature of the N-aryl substituent dictates the ability of the PC to access a charge transfer excited state. However, our current analysis of core modified phenoxazines revealed that these molecules can access a different type of CT excited state which we posit involves a core substituent as the electron acceptor. Modification of the core of phenoxazine derivatives with electron-donating and electron-withdrawing substituents was used to alter triplet energies, excited state reduction potentials, and oxidation potentials of the phenoxazine derivatives. The catalytic activity of these molecules was explored using organocatalyzed atom transfer radical polymerization (O-ATRP) for the synthesis of poly(methyl methacrylate) (PMMA) using white light irradiation. All of the derivatives were determined to be suitable PCs for O-ATRP as indicated by a linear growth of polymer molecular weight as a function of monomer conversion and the ability to synthesize PMMA with moderate to low dispersity (dispersity less than or equal to 1.5) and initiator efficiencies typically greater than 70% at high conversions. However, only PCs that exhibit strong absorption of visible light and strong triplet excited state reduction potentials maintain control over the polymerization during the entire course of the reaction. The structure-property relationships established here will enable the application of these organic PCs for O-ATRP and other photoredox-catalyzed small molecule and polymer syntheses.

Novel polyazomethines containing a N-hexylphenoxazine electron donor (D) unit and various electron acceptor (A) moieties were developed. The D–A polymers were successfully synthesized by polycondensation of 2,5-bis(p-aminophenyl)-1,3,4-oxadiazole, 4,4′-(9-fluorenylidene)dianiline, or 2,7-diaminofluorene with N-hexylphenoxazine-3,7-dicarbaldehyde, under friendly conditions. The polymer processing conditions promoted different self-assemblies during evaporation that, in turn, definitely exerted a drastic influence on the photophysical behavior of polymers. Electronic absorption, fluorescence, and electrochemistry measurements revealed that the electron-withdrawing subunit directly connected to the phenoxazine core facilitates the charge transfer character and induces a fine-tuning of HOMO–LUMO energy levels. We brought evidence, for the first time, that polaron generation in pristine, undoped films of polyazomethines is achievable. Also, it was found that fluorescence quantum yields could be tailored with o...

We report here a series of 27 10-(4-phenylpiperazin-1-yl)methanones derived from tricyclic heterocycles which were screened for effects on tumor cell growth, inhibition of tubulin polymerization, and induction of cell cycle arrest. Several analogues, among them the 10-(4-(3-methoxyphenyl)piperazine-1-carbonyl)-10H-phenoxazine-3-carbonitrile (16o), showed excellent antiproliferative properties, with low nanomolar GI50 values (16o, mean GI50 of 3.3 nM) against a large number (93) of cancer cell lines. Fifteen compounds potently inhibited tubulin polymerization. Analysis of cell cycle by flow cytometry revealed that inhibition of tumor cell growth was related to an induction of G2/M phase cell cycle blockade. Western blotting and molecular docking studies suggested that these compounds bind efficiently to β-tubulin at the colchicine binding site. Our studies demonstrate the suitability of the phenoxazine and phenothiazine core and also of the phenylpiperazine moiety for the development of novel and potent tu...

To investigate the influence of intramolecular charge transfer (CT) characteristics, rigidity, and polarity of a molecule on photophysical properties, we designed and synthesized two types of thermally activated delayed fluorescence (TADF) emitters with malononitrile and acrylonitrile moieties as electron accepting units. Their photophysical properties such as singlet–triplet energy split (ΔEST), photoluminescence quantum yields (PLQYs), and electronic structures were theoretically and experimentally evaluated. Among the synthesized materials, the emitters with an acrylonitrile moiety as an acceptor and phenoxazine, dimethylacridine, and tert-butylcarbazole as a donor revealed small ΔEST values, good PLQYs, and efficient TADF performances. In contrast, the malononitrile derivatives demonstrated high ΔEST values, very low PLQYs, and relatively poor TADF performances even though they have strong intramolecular CT characteristics and high polarity. We found that high molecular polarity and strong intramolecu...

Conventional electrochemistry and surface-enhanced Raman scattering (SERS) spectroelectrochemistry are used to probe the redox reaction of Nile Blue immobilized on gold electrodes. Covalent attachment of Nile Blue (NB) to gold through carbodiimide cross-linking shows the appearance of a second, new redox reaction, unobserved by solution phase or physisorbed NB. Each redox reaction is characterized by differential pulse voltammetry to reveal two individual one-proton, one-electron electrochemical reactions. SERS spectroelectrochemistry along with electrochemical characterization of structurally similar Cresyl Violet are used to assign the electrochemical (de)protonation of the terminal amine and phenoxazine nitrogen to the lower and higher energy redox reactions, respectively. Analysis of covalently bound NB via azide–alkyne click chemistry supports the hypothesis that the electron-withdrawing carbonyl formed during the carbodiimide cross-linking induces a change in the electronic structure of NB, causing ...

Two novel Acceptor-Donor-Acceptor (A-D-A) structured small molecular (SM-) materials POZ2 and POZ3 using an electron-rich phenoxazine (POZ) unit as a core building block were designed and synthesized. Their unique characteristics, such as suitable energy levels, strong optical absorption in the visible region, high hole mobility, and high conductivity, prompted us to use them both as p-type donor materials (DMs) in SM-bulk heterojunction organic solar cells (BHJ OSCs) and as hole transport materials (HTMs) in CH3NH3PbI3-based perovskite solar cells (PSCs). The POZ2-based devices yielded promising power conversion efficiencies (PCEs) of 7.44% and 12.8% in BHJ OSCs and PSCs, respectively, which were higher than the PCEs of 6.73% (BHJ-OSCs) and 11.5% (PSCs) obtained with the POZ3-based devices. Moreover, our results demonstrated that the POZ2 employing the electron-deficient benzothiazole (BTZ) as linker exhibited higher hole mobility and conductivity than that of the POZ3 using thiophene as linker, leading ...

This contribution presents pathways for the formation of the three nitrogenated dioxin-like species, carbazole, phenoxazine, and phenazine via unimolecular rearrangements of diphenylamine (DPA) and its nitro substituents (NDPA). The latter represent major structural entities appearing in formulations of explosives and propellants. Intramolecular H transfer from the amine group to one of the two O atoms in the nitro group denotes the most accessible route in the unimolecular decomposition of NDPA. Further unimolecular rearrangements afford phenazine and carbazole. A loss of an ortho substituent from DPA, followed by addition of an oxygen molecule, prompts the formation of carbazole and phenoxazine in a facile mechanism. The consistency between trends in Fukui-based electrophilic indices and the experimental profiles of chlorinated carbazole, phenoxazine, and phenazine suggests the formation of these species by electrophilic substitution.

A new one-pot protocol has been developed for the synthesis of benzophenazine, quinoxaline, and phenoxazine derivatives by the reaction of benzoxepine-4-carboxylates with benzene-1,2-diamines, ethane-1,2-diamine, and 2-aminophenols in the presence of Bi(OTf)3 (5 mol %) under mild conditions in very good yields. The present protocol opens a new way for C-C, C-N, and C-O bond-formation reactions in a single-step process. The structural assignment was confirmed by X-ray analysis.

Emission wavelength tuning of thermally activated delayed fluorescence from green to orange in solid state films is demonstrated. Emission tuning occurs by stabilization of the intramolecular charge transfer state between a phenoxazine (PXZ) donor unit and 2,4,6-triphenyl-1,3,5-triazine (TRZ) acceptor unit separated by a large twist angle. The emission wavelengths of mono-, bis-, and tri-PXZ-substituted TRZ exhibit a gradual red shift while maintaining a small energy gap between the singlet and triplet excited states. An organic light-emitting diode containing a tri-PXZ-TRZ emitter exhibited a maximum external quantum efficiency of 13.3 ± 0.5% with yellow-orange emission.

Ir(III) complexes of cyclometalating ligands derived from the natural product cinchonine and bent (4,6-bis(diphenylphosphino)phenoxazine (Nixantphos), 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos)) and planar diphosphine ligands (1,2-bis(diphenylphosphino)benzene (dppb)) exhibit good luminescence with quantum efficiencies higher than those of their parent congeners. Steric hindrance by both the bulky cinchonine-derived ligand and bent diphosphine could limit nonradiative energy transfer. The cinchonine-derived and parent complexes cover a broad emission range from 472 to 569 nm with quantum efficiencies up to 0.38 and lifetimes from 0.01 to 0.46 μs in degassed CH2Cl2 solution at room temperature. DFT calculations on selected examples are in good agreement with solid-state structures determined crystallographically and accurately predict wavelengths of emission by excited electron decay from a quinoline-centered orbital to an Ir 5d–phenyl molecular orbital. The complex [(pcn)2Ir(Nixantphos)][P...

New hole injection layer (HIL) materials for organic light-emitting diodes (OLEDs) based on phenothiazine and phenoxazine were synthesized, and the electro-optical properties of the synthesized materials were examined by UV−vis and photoluminescence spectroscopy, and by cyclic voltammetry. 10,10′-bis(4-tert-butylphenyl)-N7,N7′-di(naphthalen-1-yl)-N7,N7′-diphenyl-10H,10′H-3,3′-biphenoxazine-7,7′-diamine (1-PNA-BPBPOX) showed glass transition temperatures (Tg) of 161 °C, which was higher than that (110 °C) of Tris(N-(naphthalen-2-yl)-N-phenyl-amino) triphenylamine (2-TNATA), a commercial HIL material. The HOMO levels of the synthesized materials were 4.9−4.8 eV, indicating a good match between the HOMO of indium tin oxide (ITO) (4.8 eV) and the HOMO of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) (5.4 eV), a common hole transfer layer (HTL) material. Because the synthesized materials showed minimal absorption at wavelengths shorter than 450 nm, they have good potential for use as effective HIL ...

The thermodynamic driving forces (defined as the enthalpy changes or redox potentials in this work) of the 18 phenothiazines and their analogues, phenoxazine, N-methyl-dihydrophenazine, 9H-thioxanthene, 9H-xanthene and 9,10-dihydro- N-methylacridine, to release hydride, hydrogen atom, proton, and electron in acetonitrile, the thermodynamic driving forces of the radical cations of the phenothiazines and the analogues to release hydrogen atom, proton, and electron in acetonitrile, and the thermodynamic driving forces of the cations of the phenothiazines with two positive charges and their analogues to release proton in acetonitrile were estimated by using experimental methods. The effect of the remote substituents on the 11 determined thermodynamic driving forces were examined according to Brown's substituent parameters; the results show that the values of the 11 thermodynamic driving forces all are linearly dependent on the sum of Brown substituent parameters (sigma +) with very good correlation coefficients, which indicates that for any one- or multisubstituted at para- and/or meta-position phenothiazines and their various reaction intermediates, the 11 thermodynamic driving forces all can be easily and safely estimated from the corresponding Brown substituent parameters (sigma +). The relative effective charges on the center nitrogen atom in phenothiazines and their various reaction intermediates were estimated from the related Hammett-type linear free-energy relationships, which can be used to efficiently measure the electrophilicity, nucleophilicity, and dimerizing ability of the corresponding reaction intermediates of phenothiazines and their analogues. All the information disclosed in this work could not only supply a gap of the chemical thermodynamics on the mutual conversions between phenothiazines and their various reaction intermediates in solution but also strongly promote the fast development of the chemistry and application of phenothiazines and their analogues.

Substantial variations (up to factors of 5) were observed in the intramolecular charge-transfer (ICT) fluorescence quantum yields and electroluminescence efficiencies among a series of emissive bipolar donor−acceptor (D−A) materials based on a phenoxazine donor and different acceptors with a varying electron acceptor strength, including quinoline, quinoxaline, benzoquinoxaline, and benzoylquinoxaline. High-efficiency organic light-emitting diodes (OLEDs) with colors spanning the visible spectrum were achieved from the new emissive ambipolar materials. The performance of the OLEDs based on the D−A molecules decreased with increasing electron acceptor strength, largely owing to the reduction in fluorescence efficiencies. Green OLEDs (CIE = 0.27, 0.61) from a phenoxazine-quinoline molecule gave the best performance (36190 cd/m2, 10.9 cd/A at 5115 cd/m2). Red OLEDs (CIE = 0.63, 0.37) with moderate performance (9580 cd/m2, 2.3 cd/A at 230 cd/m2) were obtained from the phenoxazine-benzoylquinoxaline molecule. T...

We report the synthesis and structural, photophysical, and electrochemical properties of a series of eight new phenoxazine-based donor−acceptor molecules utilizing phenoxazine as a common donor and quinoline, quinoxaline, benzoylquinoxaline, and benzoquinoxaline as various electron acceptor moieties. The phenoxazine−phenylquinoline molecules crystallized in the monoclinic system with the space groups C2/c and P21/c, respectively, revealing a 169° dihedral angle in the phenoxazine unit. The new materials had high glass transition temperatures (128−193 °C) and ambipolar redox properties with reversible electrochemical oxidation and reduction. Their HOMO levels were at 5.1−5.2 eV, whereas their LUMO levels (2.3−3.0 eV) increased with the electron acceptor strength. The materials showed intramolecular charge transfer fluorescence in dilute solutions with emission colors varying from blue to red and a quantum yield ranging from 86% in the phenoxazine−biphenyl molecule to as low as 16% in the benzoquinoxaline-c...

Phenazine, phenothiazine, and phenoxazine are potential model compounds for flavins, minicking flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and riboflavin (VB2); each showing significant reactivity toward β-dihydronicotinamide adenine dinucleotide (NADH) and its oxidized form, NAD+. In most cases, the reaction stoichiometry is 1:1 and the associated equilibrium constants are around 104. Besides the reactivity toward NAD+ and NADH, phenazine, phenothiazine and phenoxazine adsorb strongly on indium−tin oxide (ITO) electrodes. After being adsorbed on electrodes, they still preserve their reactivity toward NAD+ and NADH. Phenazine, phenothiazine, and phenoxazine can also be attached to ITO electrodes via chemical modifications such as diazotization reduction and anodic polymerization. Irrespective of the approach, the adhesion force between the adsorbates and ITO was characterized to be >30 nN. Noticeably, when these artificial flavins were subjected to atomic force microscopy (AFM)-based f...

Melting temperatures of DNA duplexes containing the phenoxazine (P) and G-clamp (X) cytosine analogues exhibited a strong and unusual dependence on the nucleoside flanking the modified nucleobase, and the same trend was observed in PNA-DNA duplexes incorporating X in the PNA chain. Molecular dynamics simulations of the DNA duplexes show that generalized stacking (including secondary interactions of the ammonium group of X) and hydrogen bonding are good descriptors of the different duplex stabilities.

Two environmentally sensitive, long-wavelength fluorescent phenoxazine derivatives, INR and IANR, were synthesized with linkers for conjugation to the thiol group of cysteine in binding proteins. The linkers were designed based on the attachment sites at two different positions on the phenoxazine, which were chosen in order to study the orientation of the dye with respect to the binding protein. Conjugation of the dyes to the S337C maltose binding protein (MBP) mutant provided conjugates of these dyes that are capable of detecting maltose with different sensitivities. The dye INR gave a 3-fold (+200%) change in fluorescence intensity upon maltose binding when conjugated to S337C MBP with a binding constant (K(d)) of 435 microM. The fluorescence change for IANR was only 20% and the K(d) was 1.4 mM. Conformational analysis of the dyes by molecular modeling suggested that the linker in IANR imparted greater conformational freedom to the dye, resulting in little change in environment between the open and the closed-form conformations. The linker in INR, on the other hand, showed restricted motion, which placed the dye in different environments in the open and closed forms of the protein. Thus, design and placement of the linker play a critical role in the performance of these dyes as environmentally sensitive probes.

Several N,N‘-dialkyl or -diaryl substituted 1,4-benzoxazino[2,3-b]phenoxazines (1) and sulfur analogues 2 were prepared. They had low oxidation potentials (+0.30 − +0.41 V vs SCE for 1 and +0.39 − +0.55 V vs SCE for 2). N,N‘-Dimethyl-1,4-benzoxazinophenoxazine (1b) gave stable radical cation salts by electrochemical oxidation or a charge-transfer complex with TCNQ. The derived salts and the charge-transfer complex showed moderate conductivities in the range of 2.0 × 10-7 − 9.9 × 10-4 S cm-1. The N,N‘-diaryl deivatives had high thermal stability. Their thermal behavior was clarified by means of DSC. The applicability of these diaryl compounds as hole injection meterials (HIMs) in organic light-emitting diodes was studied by fabrication of a simple Alq-emitting device of ITO/HIM (40 nm)/NPB (10 nm)/Alq (50 nm)/LiF (0.5 nm)/Al (100 nm). The device ability was tested by measuring the luminous efficiency and the device decay time at a high current density (50 mA/cm2). The results were compared to a reference d...

Five new phenoxazine-based conjugated polymers, including poly(10-hexylphenoxazine-3,7-diyl), poly(10-hexylphenoxazine-3,7-diyl-alt-9,9-dihexyl-2,7-fluorene), and poly(10-hexylphenoxazine-3,7-diyl-alt-3-hexyl-2,5-thiophene), were synthesized, characterized, and successfully used as p-channel semiconductors in organic field-effect transistors. The polymers have high glass transition temperatures in the 112−230 °C range. The phenoxazine-based polymers have low ionization potentials or high-lying HOMO levels (4.8−4.9 eV), which were estimated from cyclic voltammetry. Organic field-effect transistors based on the phenoxazine polymer semiconductors have a field effect hole mobility of up to 6 × 10-4 cm2/(V s) and an on/off ratio of up to 104. These results demonstrate that phenoxazine-based conjugated polymers are promising p-type semiconductors for solution processable thin film transistors.

An optical microsensor array is described for the rapid analysis of silver ions at low parts per trillion levels. Because the ionophore o-xylylenebis(N,N-diisobutyldithiocarbamate) (Cu-I) was reevaluated and shown to exhibit excellent selectivity for silver ions, ion-selective electrode (ISE) membranes were optimized and found to exhibit the lowest reported detection limit so far (3 x 10(-10) M). A corresponding Ag+-selective fluorescent optical microsensor array for the rapid sensing of trace level Ag+ was then developed. It was fabricated using plasticized PVC-based micrometer-scale fluorescent microspheres that were produced via a sonic particle casting device. They contained 156 mmol/kg Cu-I, 10 mmol/kg 9-(diethylamino)-5-[4-(15-butyl-1,13-dioxo-2,14-dioxanodecyl) phenylimino]benzo[a]phenoxazine (chromoionophore VII, ETH 5418), 2.3 mmol/kg 1,1' '-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (internal reference dye), and 14 mmol/kg sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate and were deposited onto the etched distal end of a 3200-microm-diameter optical fiber bundle. The microarray was characterized by fluorescence spectroscopy in samples containing 10(-12)-10(-8) M AgNO3 at pH 7.4, with selectivity characteristics comparable to the corresponding ISEs. The response time of the microsensor array was found to be less than 15 min for 10(-9) M AgNO3, which is drastically shorter than earlier data on optode films (8 h) and corresponding ISEs (30 min). A detection limit of 4 x 10(-11) M for Ag+ was observed, lower than any previously reported optode or silver-selective ISE. The microsensor array was applied for measurement of free silver levels in buffered pond water samples.

[structure: see text] Peptide nucleic acid (PNA) monomers containing the tricyclic cytosine analogues phenoxazine, 9-(2-aminoethoxy)phenoxazine (G-clamp), and 9-(3-aminopropoxy)phenoxazine (propyl-G-clamp) have been synthesized. The modified nucleobases were incorporated into PNA oligomers using Boc-chemistry for solid-phase synthesis. PNAs containing single G-clamp modifications exhibit significantly enhanced affinity toward RNA and DNA targets relative to unmodified PNA while maintaining mismatch discrimination. These PNA G-clamp modifications exhibit the highest increase in affinity toward nucleic acid targets reported so far for PNA modifications.

A homogeneous hydroformylation catalyst, designed to produce selectively linear aldehydes, was covalently tethered to a polysilicate support. The immobilized transition-metal complex [Rh(A)CO]+(1+)), in which A is N-(3-trimethoxysilane-n-propyl)-4,5-bis(diphenylphosphino)phenoxazine, was prepared both via the sol-gel process and by covalent anchoring to silica. 1+ was characterized by means of (31)P and (29)Si MAS NMR, FT-IR, and X-ray photoelectron spectroscopy. Polysilicate immobilized Rh(A) performed as a selective hydroformylation catalyst showing an overall selectivity for the linear aldehyde of 94.6% (linear to branched aldehyde ratio of 65). In addition 1-nonanol, obtained via the hydrogenation of the corresponding aldehyde, was formed as an unexpected secondary product (3.6% at 20% conversion). Under standard hydroformylation conditions, 1+ and HRh(A)(CO)(2)(1) coexist on the support. This dual catalyst system performed as a hydroformylation/hydrogenation sequence catalyst (Z), giving selectively 1-nonanol from 1-octene; ultimately, 98% of 1-octene was converted to mainly 1-nonanal and 97% of the nonanal was hydrogenated to 1-nonanol. The addition of 1-propanol completely changes Z in a hydroformylation catalyst (X), which produces 1-nonanal with an overall selectivity of 93%, and completely suppresses the reduction reaction. If the atmosphere is changed from CO/H(2) to H(2) the catalyst system is switched to the hydrogenation mode (Y), which shows a clean and complete hydrogenation of 1-octene and 1-nonanal within 24 h. The immobilized catalyst can be recycled and the system can be switched reversibly between the three "catalyst modes" X, Y, and Z, completely retaining the catalyst performance in each mode.

Starting with the published 2.0 A X-ray crystal structure of the transthyretin·(flufenamic acid)2 complex, a simple structure-based ligand design strategy was employed to conceive of N-phenyl phenoxazine transthyretin (TTR) amyloid fibril inhibitors. Fifteen N-phenyl phenoxazines were chemically synthesized and evaluated using a quantitative amyloid fibril assay in vitro. The structure of one of the two most active phenoxazines, 4, bound to TTR was solved to a resolution of 1.9 A to understand the structural basis of its efficacy. N-phenyl phenoxazine 4 binds similar to the orientation anticipated, although not as deeply into the channel as expected. Like flufenamic acid, 4 mediates binding-induced conformational changes that enable intersubunit H-bonding in tetrameric TTR which may be important for preventing fibril formation. Analytical ultracentrifugation analysis demonstrates that 4 blocks the first step of TTR amyloid fibril formation, that is, tetramer dissociation to the alternatively folded amyloi...

As part of a larger search for potent as well as selective inhibitors of dihydrofolate reductase (DHFR) enzymes from opportunistic pathogens found in patients with AIDS and other immune disorders, N-[(2,4-diaminopteridin-6-yl)methyl]dibenz[b,f]azepine (4a) and the corresponding dihydrodibenz[b,f]azepine, dihydroacridine, phenoxazine, phenothiazine, carbazole, and diphenylamine analogues were synthesized from 2, 4-diamino-6-(bromomethyl)pteridine in 50-75% yield by reaction with the sodium salts of the amines in dry tetrahydrofuran at room temperature. The products were tested for the ability to inhibit DHFR from Pneumocystis carinii (pcDHFR), Toxoplasma gondii (tgDHFR), Mycobacterium avium (maDHFR), and rat liver (rlDHFR). The member of the series with the best combination of potency and species selectivity was 4a, with IC(50) values against the four enzymes of 0. 21, 0.043, 0.012, and 4.4 microM, respectively. The dihydroacridine, phenothiazine, and carbazole analogues were also potent, but nonselective. Of the compounds tested, 4a was the only one to successfully combine the potency of trimetrexate with the selectivity of trimethoprim. Molecular docking simulations using published 3D structural coordinates for the crystalline ternary complexes of pcDHFR and hDHFR suggested a possible structural interpretation for the binding selectivity of 4a and the lack of selectivity of the other compounds. According to this model, 4a is selective because of a unique propensity of the seven-membered ring in the dibenz[b,f]azepine moiety to adopt a puckered orientation that allows it to fit more comfortably into the active site of the P. carinii enzyme than into the active site of the human enzyme. Compound 4a was also evaluated for the ability to be taken up into, and retard the growth of, P. carinii and T. gondii in culture. The IC(50) of 4a against P. carinii trophozoites after 7 days of continuous drug treatment was 1.9 microM as compared with previously observed IC(50) values of340 microM for trimethoprim and 0.27 microM for trimetrexate. In an assay involving [(3)H]uracil incorporation into the nuclear DNA of T. gondii tachyzoites as the surrogate endpoint for growth, the IC(50) of 4a after 5 h of drug exposure was 0.077 microM. The favorable combination of potency and enzyme selectivity shown by 4a suggests that this novel structure may be an interesting lead for structure-activity optimization.

Bright and efficient green light-emitting diodes were achieved from the intramolecular charge-transfer fluorescence of new donor−acceptor molecules incorporating phenoxazine as the donor and phenylquinoline as the acceptor.

Platicized poly(vinyl chloride) (PVC) membranes based on a hydrogen ion-selective chromoionophore optically sense gaseous sulfur dioxide in the presence of humidity. It the membrane additionally contains a lipophilic alcohol or its matrix consists of hydroxylated PVC, it also responds to dry SO 2 . In either case, sensitivity and selectivity of the optodes can be improved by incorporating a lipophilic aldehyde into the membrane phase. The chemical equilibria involved in the different sensor types are discussed. With octadecyl 4-tormylbenzoate (ETH 5444) as the lipophilic ahdehyde and 9-(diethylamino)-5-[(2-octyldecyl)amino]-5H-benzo[a]phenoxazine (ETH 5350) as the basic chromoionophore, SO 2 concentrations as low as 4 ppb v are determined

Hydrogen peroxide is efficiently electroreduced at an electrode modified with a hydrophilic, permeable film of horseradish peroxidase (HRP) covalently bound to a 3-dimensional epoxy network having polyvinyl pyridine (PVP)-complexed Os(bpy)2Cl+3/+2 redox centers. The sensitivity of the resulting H202 cathode at O.OV(SCE) is 1Acm(-2)M(-1). Its current increases linearly with H2O2 concentration in the 1x10(-7)M(-)2x10(-4)M range. Related NAD(P)H cathodes are based on stoichiometric homogeneous reduction of 02 to H202 by NADH or NAD(P)H. The reduction involves two known steps. In the first step, NAD(P)H transfers two electrons and a proton to a dissolved quinoid. The quinoids are typically derived of phenazines, however phenothiazine and phenoxazine derivatives are also useful. In the second step, two electrons and a proton are transferred from the reduced quinoid to O2. This reaction produces H202 and the original quinoid. Because the two reactions are quantitative, the sensitivity and the linear range of the resulting NADH and NADPH electrodes are identical with those of the H202 electrode, 1Acm(-2)M(-1) and 1x10(-7)M (-2)2x10(-4)M respectively.