Synthesis of N-substituted phenoxazine polymers bearing vinyl backbone

Vinyl monomers bearing N-substituted phenoxazine or 2,8-dimethylphenoxazine units were synthesized starting with the corresponding phenoxazines. N-substituents were 2-vinylbenzyl-oxycarbonylethyl group prepared via 2-carboxyethyl group, 3-methacrylamido-, 3-acrylamido-, or 3-(4-styrenesulfonamido)-propyl group prepared via 3-aminopropyl group, vinylbenzyl, or 2-vinyloxyethyl group attached by the displacements of sodium salts of the phenoxazines to the chlorides, and 2-methacryloyl- or 2-acryloyl-oxyethyl group prepared via 2-hydroxyethyl group. Free-radical polymerixations of these novel monomers proceeded smoothly, except those with 2-vinyloxyethyl group, which were susceptible to BF₃-etherate. Changes of the visible absorption spectrum of iodine in THF with addition of the monomers and polymers were considerable, with the appearance of new absorption peaks or shoulders in major cases.     

Photomediated core modification of organic photoredox catalysts in radical addition: mechanism and applications

Dihydrophenazines and their analogues have been widely used as strong reducing photoredox catalysts in radical chemistry, such as organocatalyzed atom transfer radical polymerization (O-ATRP). However, when dihydrophenazines were employed as organic photoredox catalysts (OPCs) to mediate O-ATRP, the initiator efficiency was nonquantitative due to cross-coupling between dihydrophenazines and radical species. Here, a new kind of core modification for dihydrophenazines, phenoxazines and phenothiazines was developed through this cross-coupling process. Mechanistic studies suggested that the radical species would be more likely to couple with OPC'' radical cations rather than the ground-state OPC. Core modification of OPCs could stabilize the radical ions in an oxidative quenching catalytic cycle. Significantly, core modifications of OPCs could lower the energy of light required for photoexcitation. Compared with their noncore-modified counterparts, all the core-modified dihydrophenazines and phenoxazines exhibited efficient performance in controlling O-ATRP for the synthesis of poly(methyl methacrylate) with higher initiator efficiencies under the irradiation of simulated sunlight.

Photomediated core modification of organic photocatalysts through a radical/radical cation cross-coupling process enables the ability to stabilize radical ions and prevent undesirable side reactions.     

Transition-metal-free intramolecular N-arylations

N-Substituted phenoxazines and related aza analogs have been prepared from N-acetylated aryloxy anilides by transition-metal-free, base-catalyzed cyclization reactions. In the presence of a mixture of 10 mol % of N,N'-dimethylethylenediamine (DMEDA) and 2 equiv of K(2)CO(3) in toluene at 135 °C the products are obtained in high yields.     

The carboxyl derivatives of 6,8-di-(tert.-butyl)phenoxazine: Synthesis,oxidation reactions and fluorescence

New carboxyl-containing o-aminophenols and phenoxazines were synthesized by condensation of 3,5-di-(tert.-butyl)-quinone with p-aminobenzoic and anthranilic acids. Oxidative transformations of the o-aminophenols and intermediate o-iminoquinones occur with the formation of the ESR detected phenoxazinyl radicals, which furthermore transform to phenoxazines or the dimeric products emerged through the radical attack at the C1 carbon of a formed phenoxazine. Molecular structure of the dimer obtained by oxidation of methyl ester of 4-[3,5-di-(tert.-butyl)-1-(2′-hydroxyphenyl)amino]benzoic acid was X-ray determined. Reaction of 4-[3,5-di-(tert.-butyl)-1-(2′-hydroxyphenyl)amino]benzoic acid with thionyl chloride gives rise to the formation of a derivative of 2-oxido-3H-benzo[d,j][1,2,3]oxathiazol system, the structure of which was established using X-ray crystallography. Solutions of methyl-6,8-di-(tert.-butyl)-10H-phenoxazine-3-carboxylate solvents display intense fluorescence covering a broad spectral region in the range of 400–600?nm.     

Synthesis of polycyclic mixed phenothiazine-phenoxazine organic dyes

A convenient synthesis of new polycyclic mixed phenothiazine-phenoxazine compounds is described. The cross-coupling of 2,4-diaminothiophenol with 2,3-dichloro-1,4-naphthoquin one at room temperature gave reddish brown 10-amino-6-chlorobenzo[a]phenoxazin-5-one which was converted into a benzoxazinophenothiazin-12-amine in 58% yield via reaction with 2-aminothiophenol under anhydrous basic conditions. A three-component one-pot synthesis improved the yield of benzoxazinophenothia-12-amine to 81% a in shorter time compared to two steps reactions. The synthesis of new azomethine derivatives of benzo[a]benzo[5,6] [1,4] oxazino [3,2-c] phenothiazin-12-amine with extended conjugations and excellent yields were also reported. The structural assignments of the prepared compounds were established by combine Ultraviolet-Visible, Fourier Transform Infrared, ¹H and ¹³C Nuclear Magnetic Resonance Spectroscopies, Mass Spectrometry and elemental analytical data. The ease of preparations in high yields and their intense colourations make these compounds applicable as dyestuffs.     

Some studies in the phenoxazine series

In the cyclization of 2-chloroaryl 2-arenesulfamidoaryl ethers to N-arylsulfonylphenoxazines rearrangement of the latter to C-arylsulfonyl-substituted phenoxazines is observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1596–1598. December, 1975.     

Nucleophilic addition to the phenoxazonium cation

At the instant of its formation of oxidation of phenoxazine with ferric chloride, the phenoxazonium cation adds arenesulfinate and nitrite ions to give 3-arylsulfonyl- and 3-nitrophenoxazines, respectively. It is shown that the introduction of a second sulfonyl group proceeds more slowly and gives 3,7-di(arylsulfonyl)phenoxazines in low yields. The PMR spectra of the synthesized compounds are examined in comparison with 3-substituted phenothiazines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 616–618, May, 1977.     

Modular Synthesis of Triarylamines and Poly(triarylamine)s through a Radical Mechanism

A modular protocol for the triarylamine synthesis has been developed using diarylamines and electron-rich arenes, such as phenols, as the building blocks. The KI/KIO₄ system proves to be highly efficient for the cross-dehydrogenative coupling of phenothiazines/phenoxazines with phenols/anilines. A wide range of functional groups attached to both coupling partners were well tolerated. Through the manipulation of reaction temperatures, the sequential assembly of bis-triarylamines could be achieved to provide the unsymmetrically bis-aminated phenols efficiently. Furthermore, the multiple aminated polyphenols were rapidly constructed in good to high yields by a single operation.     

Formation of benzo[a]phenoxazine derivatives by triethylphosphite-induced deoxygenation of 1-(2-nitrophenoxy) and 2-(2-nitrophenoxy)naphthalenes

Reaction of 1-(2-nitrophenoxy)naphthalene or its β-isomer $\text{7}$ with triethylphosphite produces benzo[a]phenoxazines $\text{8}$ and $\text{10}$, through the intermediate $\text{6}$.     

Étude D'une Série de Phénoxazines et D'azaphénoxazines par Spectrométrie de Masse

Mass spectra of substituted phenoxazines and azaphenoxazines have been determined and are discussed here. These compounds are characterised by hydrogen on the heterocyclic nitrogen and aromatic rings with nitro groups and chlorine as substituents. The fragmentation patterns are explained by known mechanisms. An interpretation of almost all the peaks is offered. The presence of the substituents causes a complete change in the fragmentation patterns compared with the unsubstituted phenoxazine. This is due to changes in charge localisation, caused by the substituents. Isomerisation of the nitro group to the nitroso group gives rise to a particular fragmentation route.     

New Activation Method of Chloroenaminone Quinones for Synthesis of Polynuclear Heterocyclic Systems

The chlorine atom of chloroenamineone in the quinonoid compounds 1a-f and 7 was activated by the reaction with benzenesulphonyl chloride to form naphthoquinonid moiety fused with linear or angular heterocyclic systems as carbazoles 2a-c , phenazines 3a , b and 5a-c , phenoxazines 3c phenothiazine 3d , quinoxalinophenazine 6a , quinoxalinophenoxazine 6b , quinoxalinophenthiazine 6c , oxadiazine 8 , thiadiazine 9 , and pyrazole 10 . The mechanism of the latter derivative was discussed. Spectroscopic data of all new products are given. Additionally, the antimicrobial activity of some reported compounds was screened.     

Oxazolo analogs of the actinomycin D chromophore

Condensation of a tricyclic phenoxazin-2-amino-3-one (a model for the actinomycin D ring system) with acetaldehyde or benzaldehyde or with pyruvic acid as an acetaldehyde precursor gave tetracyclic 5H-oxazolo[4,5-b]phenoxazines. The pyruvic acid reaction proceeds efficiently in one step. The latter compounds were oxidized in a novel reaction by 2,3-dichloro-5,6-dicyano-benzoquinone exclusively at position 8 in the benzenoid ring. Uv, ir, nmr, and mass spectrometric data are reported.     

Aminobenzoates as building blocks for natural product assembly lines

The ortho-, meta-, and para- regioisomers of aminobenzoate are building blocks for a wide range of microbial natural products. Both the ortho-isomer (anthranilate) and PABA derive from the central shikimate pathway metabolite chorismate while the meta-isomer is not available by that route and starts from UDP-3-aminoglucose. PABA is largely funnelled into folate biosynthesis while anthranilate is the scaffold for biosynthetic elaboration into many natural heterocycles, most notably with its role in indole formation for tryptophan biosynthesis. Anthranilate is also converted to benzodiazepinones, fumiquinazolines, quinoxalines, phenoxazines, benzoxazolinates, quinolones, and phenazines, often with redox enzyme participation. The 5-hydroxy form of 3-aminobenzaote is the starter unit for ansa-bridged rifamycins, ansamitocins, and geldanamycins, whereas regioisomers 2-hydroxy, 4-hydroxy and 2,4-dihydroxy-3-aminobenzoate are key components of antimycin, grixazone, and platencin and platensimycin biosynthesis, respectively. The enzymatic mechanisms for generation of the aminobenzoate regioisomers and their subsequent utilization for diverse heterocycle and macrocycle construction are examined.     

Phenoxazine‐based Near‐infrared Fluorescent Probes for the Specific Detection of Copper (II) Ions in Living Cells

Abstract : 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.     

Fuctionalization of Linear and Angular Phenothiazine and Phenoxazine Ring Systems via Pd(0)/XPhos Mediated Suzuki‐Miyaura Cross‐coupling Reactions

Chloro‐substituted phenothiazines and phenoxazines were successfully derivatized with phenylboronic and styrylboronic acids using Suzuki–Miyaura cross‐coupling reaction catalyzed by Pd(0)/XPhos for the first time in good yields. The protocol employed 4 mol% Pd and 7 mol% XPhos with K₃PO₄ in acetonitrile at 80°C. The reaction condition is compatible with carbonyl and unprotected N–H groups in substrates. Structural assignments were established by combined spectroscopic (UV, IR, ¹H, and ¹³C NMR), MS, and elemental analytical data.     

Photochemical and thermal transformations of 1-aryloxy-2- and 4-azidoanthraquinones

The photolysis of 1-aryloxy-2-azidoanthraquinones (3) in benzene is described herein which gave 1-hydroxy-2-arylaminoanthraquinones (4) and two types of 5H-naphtho[2,3-c]phenoxazine-8,13-diones (5 and 6). Thermolysis of 3 yielded only one of phenoxazines 5 and small amount of 4. On the other hand thermolysis of 3 in the presence of phenols gave phenoxazine 6 as a major product. The mechanism of the photolysis and thermolysis of 2-azido-1-aryloxyanthraquinones (3) is proposed and supported by the results from semiempirical calculations. A relative contribution of the primary photoreactions-azido group dissociation and aryl group migration was estimated to be 3:1. Photolysis and thermolysis of 4-azido-1-(p-tert-butylphenoxy)-9,10-anthraquinone (8) gave 3-(p-tert-butylphenoxy)-anthra[1,9-cd]-izoxazole-6-one (9) as the only product.     

Photocyclization of 2-azido-1-(4-<Emphasis Type="Italic">tert</Emphasis>-butylphenoxy)-9,10-anthraquinone in the presence of substituted phenols

New types of phototransformations in the quinone series, viz., photocyclizations of 1-aryloxy-2-azido-9,10-anthraquinone in the presence of phenols, were studied. The photolysis affords mainly 5H-naphtho[2,3-c]phenoxazine-8,13-diones, in which the nitrogen atom is covalently bound to the phenyl ring of the attached phenol. As a result, complex polycyclic derivatives of phenoxazines were prepared in high yields in one step. Dedicated to the memory of Academician N. N. Vorozhtsov on the 100th anniversary of his birth. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1089–1093, June, 2007.     

Synthesis of vinyl polymers with pendant phenoxazinyl group

Vinyl monomers bearing phenoxazine units, were synthesized: 2-vinyl-phenoxazine starting with phenoxazine in a five-step synthesis; 3-acrylamido- or 3-methacrylamido-phenoxazines with or without 10-PhCH₂ or 10-Me-substituent starting with o-benzylideneaminophenol or o-anisidine via 3-aminophenoxazines; and 3-(p-styrenesulfonamido)phenoxazines with or without 10-PhCH₂- or 10-Me-substituent, also via 3-aminophenoxazines. Polymerizations of these noval monomers proceeded smoothly, except those having no 10-substituent. Changes of the visible absorption spectrum of iodine in THF with addition of the polymers and oligomers thus prepared were considerable, with the appearance of new absorption peaks for polymers with 10-Me-substituent.     

Aqueous photopolymerization with visible‐light photoinitiators: Acrylamide polymerization photoinitiated with a phenoxazine dye/amine system

We studied the photoinduced electron‐transfer polymerization of acrylamide with, as a visible‐light initiator, the heterocycle‐N‐oxide resazurin in the presence of triethanolamine. The irradiation of resazurin produces resorufin, which also absorbs in the visible region. Both phenoxazine dyes in the presence of the amine are efficient photoinitiators of acrylamide polymerization in an aqueous medium. The polymerization rates were measured at several amine concentrations. These values increase with the amine concentration, reaching a maximum value; further amine addition slightly decreases the polymerization rate. Time‐resolved photolysis studies of the dyes were carried out under the polymerization conditions. The quenching of the dye excited states by the amine was analyzed with static‐fluorescence and laser‐flash photolysis. These data were used for fitting curves of the polymerization rate versus the amine concentration, and it was concluded that the interaction of triplet excited dyes with the amine leads to acrylamide polymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4074–4082, 2001     

Highly Efficient Candlelight Organic Light-Emitting Diode with a Very Low Color Temperature

Low color temperature candlelight organic light-emitting diodes (LEDs) are human and environmentally friendly because of the absence of blue emission that might suppress at night the secretion of melatonin and damage retina upon long exposure. Herein, we demonstrated a lighting device incorporating a phenoxazine-based host material, 3,3-bis(phenoxazin-10-ylmethyl)oxetane (BPMO), with the use of orange-red and yellow phosphorescent dyes to mimic candlelight. The resultant BPMO-based simple structured candlelight organic LED device permitted a maximum exposure limit of 57,700 s, much longer than did a candle (2750 s) or an incandescent bulb (1100 s) at 100 lx. The resulting device showed a color temperature of 1690 K, which is significantly much lower than that of oil lamps (1800 K), candles (1900 K), or incandescent bulbs (2500 K). The device showed a melatonin suppression sensitivity of 1.33%, upon exposure for 1.5 h at night, which is 66% and 88% less than the candle and incandescent bulb, respectively. Its maximum power efficacy is 23.1 lm/W, current efficacy 22.4 cd/A, and external quantum efficiency 10.2%, all much higher than the CBP-based devices. These results encourage a scalable synthesis of novel host materials to design and manufacture high-efficiency candlelight organic LEDs.