A convenient, rapid and eco-friendly synthesis of isoxazoline heterocyclic moiety containing bridge at 2°-amine as potential pharmacological agent

2-Amino-4-(coumarin-3-yl)-thiazole (1) reacted with acetyl chloride gives compound (2) which on further refluxed with various aromatic aldehydes gives compound (3a-j). Thus obtained (3a-j) on further condensed with NH₄OH.HCl using NaOH as a catalyst afforded isoxazoles (4a-j). All the synthesized compounds characterized on the basis of the IR, ¹H NMR, ¹³C NMR and elemental analysis. All the compounds have been screened for antibacterial activity against bacteria (Gram + ve) & (Gram ? ve) and antifungal activity.     

Stereochemie von Metallocenen, 36. Mitt.:

The two optically active methylbenchrotrenecarboxylic acids (1 a and1 b) with absolute configurations established by the X-ray method were chemically correlated with several o-and m-disubstituted benchrotrenes. Curtius degradation of the carboxylic acids1 afforded amino methylbenchrotrenes (4) which were also obtained by reduction of the active aminobenchrotrenecarboxylic acids (2). From the amines4 by diazotation and methylation methoxy methylbenchrotrenes (5) were accessible which in turn were prepared by reduction of the active methoxybenchrotrene carboxylic acids (3). The m-isomer3 b was transformed by Curtius degradation into m-methoxy aminobenchrotrene (6 b). Thereby the absolute configurations of some sixty optically active benchrotrene derivatives are now established.     

Synthesis, molecular structures, and properties of heterometallic cobalt tetramethylcyclobutadiene complexes (C4Me4)Co(CO)2TePh, (C4Me4)Co(CO)2TePh[W(CO)5], and Me4C4Co(μ3-S)2Cr2Cp2(μ-SC4H9)

The reaction of Cb*Co(CO)₂I (1) (Cb* is tetramethylcyclobutadiene) with sodium phenyltelluride afforded the mononuclesar complex Cb*Co(CO)₂TePh (2). The reaction of the latter with W(CO)₅(THF) produced the Cb*Co(CO)₂TePh[W(CO)₅] compound (4). The reaction of 1 with the Cp₂Cr₂(SCMe₃)₂S complex gave the heterometallic cluster Cb*Co(μ₃-S)₂Cr₂Cp2 (μ-SCMe₃) (5). Complexes 2, 4, and 5 are diamagnetic. Their structures were determined by X-ray diffraction. Complex 2 contains the Co-Te bond (2.585(1) Å); complex 4, the Co-Te (2.558(8) Å) and W-Te (2.8467(6) Å) bonds. Complex 5 has the stable triangular sulfide-and tert-butylmercaptide-bridged core Cr₂Co (Cr-Cr and Cr-Co bond lengths are 2.626(2) and 2.673(2) Å, respectively) with Cp ligands at the chromium atoms and a Cb* ligand at the cobalt atom. Complex 5 was characterized by cyclic voltammetry. The thermolysis of complex 4 was studied.     

Divalent Pb(0) compounds

Density functional theory (DFT) calculations have been carried out on four novel dicoordinated lead compounds PbL₂ where L is an N-heterocyclic ylidene or a five-membered cyclic ylidene (1Pb, 2Pb, 4Pb, 5Pb) and for a plumbylene-coordinated carbone CL₂ (3Pb). The theoretically predicted equilibrium geometries and the first and second proton affinities of 1Pb?C5Pb are reported. Geometry optimizations have also been carried out for the complexes with one and two BH₃ ligands 1Pb(BH ₃ )?C5Pb(BH ₃ ) and 1Pb(BH ₃ ) ₂ ?C5Pb(BH ₃ ) ₂ , and for the transition metal complexes 1PbW(CO) ₅ ?C5PbW(CO) ₅ and 1PbNi(CO) ₃ ?C5PbNi(CO) ₃ . The results suggest that the molecules 1Pb, 2Pb and 4Pb possess properties which identify them as divalent Pb(0) compounds (plumbylones). This comes to the fore by the theoretically predicted second PAs which are very large for a lead compound and (for 1Pb and 4Pb) by the BDE of the second BH₃ ligand. Compound 3Pb should be considered as a plumbylene-coordinated divalent C(0) compound (carbone) which has a very high second PA of 195.1?kcal/mol. The geometry optimization of 5Pb gives an equilibrium structure which identifies the molecules as divalent Pb(II) compound, i.e., as a plumbylene.     

Synthesis and anti-viral activities of some 3-(naphthalen-1-ylmethylene)-5-phenylfuran-2(3H)-one candidates

3-(Naphthalen-1-ylmethylene)-5-phenylfuran-2(3H)-one 1 was prepared and converted into a variety of heterocyclic systems of synthetic and biological importance. Benzylamine was reacted with furanone 1 to afford compounds 2 and 3 according to the reaction conditions. Butanamide 2 was reacted with thionyl chloride or thiourea to give derivatives 4 and 5, respectively. Compound 3 was reacted with ethyl cyanoacetate to give the corresponding pyrrolopyridine derivative 6. Treatment of 1 with hydrazine hydrate afforded compounds 7 and 8 according to the reaction conditions. Also, compound 1 was reacted with phenyl hydrazine, hydroxyl amine, malononitrile or thiourea to give compounds 9–12, respectively. Cyclization of 7 with ethoxymethylene-malononitrile, ethyl-(ethoxymethylene)cyanoacetate, carbon disulphide or acetylacetone afforded the corresponding compounds 13–16, respectively. Condensation of 7 with p-nitrobenzaldehyde gave the corresponding hydrazone 17, which was treated with thioglycolic acid or chloroacetyl chloride to give compounds 18 and 19, respectively. Also, most of the prepared products were tested for anti-avian influenza virus and revealed promising antiviral activity against H5N1 virus [A/Chicken/Egypt/1/2006 (H5N1)] by determination of both TC ₅₀ and ED ₅₀ and confirmed by plaque reduction assay on MDCK cells. Compounds 7, 8, 11, 12 and 13 showed the highest effect compared with the other tested compounds.     

Heterometallic derivatives of dicarbonylcyclopentadienylrhenium disulfide containing chromium pentacarbonyl and bis(triphenylphosphine)platinum

The reaction of Cp′Re(CO)₂THF (Cp′ = C₅H₄Me), THF is tetrahydrofuran) with sulfur affords Cp′Re(CO)₂S₂(I) and [Cp′Re(CO)₂]₂S (II). The synthesized compounds are isolated chromatographically and characterized by X-ray diffraction analysis. The adduct Cp′Re(CO)₂S₂Cr(CO)₅ (III) is synthesized by the reaction of compound I with Cr(CO)₅(THF). The adduct CpRe(CO)₂S₂Cr(CO)₅ (IV) is obtained similarly from known CpRe(CO)₂S₂ and Cr(CO)₅(THF). The reaction of compound I with (PPh₃)₂Pt(C₂Ph₂) results in the removal of Ph₂C₂ and one sulfur atom to form Cp′Re(CO)₂SPt(PPh₃)₂ (V). The structures of compounds I–V are determined by X-ray diffraction analysis (CIF files CCDC nos. 984554 (I), 984555 (II), 984556 (III), 984557 (IV), and 984558 (V)). Compound I contains the three-membered cycle ReS₂ with the ordinary S-S bond (2.044(4) Å) and shortened Re-S bonds (average 2.434(3) Å). The three-membered cycle Re₂S containing the ordinary Re-Re bond (2.932(1) Å) and shortened Re-S bonds (2.371(1) Å) is observed in compound II. In compounds III and IV, the formation of the ordinary S-Cr(CO)₅ bond (2.406(1) Å) with one of the sulfur atoms almost does not change the geometry of the ReS₂ fragment. The thermal decomposition of compound III proceeds with the elimination of six CO ligands in the range 110–160°C and then with the loss of CO and Cp′ in the range 160–430°C and the formation of the inorganic residue ReCrS₂. Compound V contains the triangular framework ReSPt with the ordinary Pt-Re bond (2.7882(3) Å) and substantially shortened bonds Re-S (2.3984(9) Å) and Pt-S (2.2724(8) Å). It is assumed that compounds II and V can be presented as products of the π-coordination of the double bonds in Cp′(CO)₂Re=S with the Cp′Re(CO)₂ or Pt(PPh₃)₂ groups, respectively.     

Synthesis and characterization of glycol-modified vanadium(V) oxoisopropoxide and their oximato derivatives: sol–gel transformations of [VO(OPr i )3], [VO{OCH2CH2OCH2CH2O}{OPr i }] and [VO{OCH2CH2OCH2CH2O}{ON=C(CH3)(C4H3S-2)}] to vanadia

Reaction of [VO(OPr ⁱ )₃] (1) with [O(CH₂CH₂OH)₂] in 1:1 molar ratio in anhydrous benzene yield glycol-modified precursor, [VO{OCH₂CH₂OCH₂CH₂O}{OPr ⁱ }] (2). Further reactions of (2) with internally functionalized oximes in anhydrous benzene yield heteroleptic complexes of the type [VO{OCH₂CH₂OCH₂CH₂O}{ON=C(R)(Ar)}] (3–8) {where R=CH₃, Ar=C₄H₃O-2 (3), C₄H₃S-2 (4), C₅H₄N-2 (5); and when R=H, Ar=C₄H₃O-2 (6), C₄H₃S-2 (7), C₅H₄N-2 (8)}. All these derivatives have been characterized by elemental analyses, molecular weight measurements and spectroscopic techniques. The crysoscopic molecular weight measurement as well as FAB mass study suggests dimeric nature of (2). However, FAB mass spectrum of (4), and the crysoscopic molecular weight measurements of (3), (4), (5) and (6) indicate the monomeric behavior of the oximato derivatives (3–8). Hexa-coordination around vanadium(V) has been proposed for both monomeric and dimeric derivatives. Sol–gel transformations of (1), (2) or (4) to vanadia [(a), (b) or (c), respectively] have been carried out at low sintering temperature (600 °C). The XRD patterns of (a), (b) or (c) indicate formation of a single orthorhombic phase in all the three cases. The SEM images suggest grain like [for (a) and (b)] and rod like [for (c)] morphology of the crystallites. IR, Raman spectra as well as EDX analyses indicate formation of pure vanadia. Absorption spectra of the vanadia (b) and (c) suggest energy band gaps of 2.53 and 2.65 eV, respectively.     

Fullerenes (C60) versus heteroazafullerenes (C59N); a photophysical comparison of their monoadducts and hexaadducts

The singlet and triplet excited state properties of a series of fullerene derivatives (C₆₀) are compared to those of the corresponding heteroazafullerenes derivatives (C₅₉N) by employing a variety of steady-state and time-resolved photophysical assays. The most far-reaching results infer that the C₅₉N (2, 5) analogous of C₆₀ (1, 4) are characterized by shorter singlet lifetimes (1.01/0.57 ns versus 1.80/1.75 ns) and weaker fluorescence quantum yields (1.6 × 10^-4/2.1 × 10^-4 versus 6.0 × 10^-4/1.09 × 10^-3). This general conclusion applies for the monoadduct series (1, 2) and also for the highly functionalized hexaadducts (4, 5). Similarly, higher singlet energies (1.89 eV (4) versus 1.79 eV (1)) come together with higher fluorescence quantum yields for the hexaadducts than for the monoadducts.     

Dicarbonylcyclopentadienyltellurophenyliron complexes as ligands

The reaction of CpFe(CO)₂TePh (I) with ferricinium hexafluorophosphate as an oxidant affords ionic complex {[CpFe(CO)₂]₂(μ-TePh)}⁺PF ₆ ^? (II) with the simultaneous formation of diphenylditellurium. The decarbonylation of compound II by Me₃NO followed by the addition of complex I affords trinuclear complex {[CpFe(CO)₂(μ-TePh)]₂Fe(CO)Cp}PF₆ (III). The corresponding tetrafluoroborate (IV) is synthesized similarly. The heating of compound I with PPh₃ gives CpFe(CO)(PPh₃)TePh (V) that reacts with ionic complex [CpMn(CO)₂(NO)]PF₆ (VI) to form binuclear heterometallic ionic complex [CpFe(CO)(PPh₃)(μ-TePh)Mn(CO)(NO)Cp]PF₆ (VII). A similar reaction of Cp′Fe(CO)₂TePh (Cp′ is methylcyclopentadienyl) with compound VI affords heterometallic [Cp′Fe(CO)₂(μ-TePh)Mn(CO)(NO)Cp]PF₆ (VIII). The structures of compounds II, IV, VII, and VIII are determined by X-ray diffraction analysis (CIF files CCDC 963285, 963286, 963288, and 963289, respectively).     

Structures and properties of novel 5,15-di[4-(5-acetylsulfanylpentyloxy)phenyl] porphyrin derivatives: Density functional theory calculations

Density functional theory (DFT) calculations have been carried out in order to compare the molecular structures, atomic charges, molecular orbitals, electronic absorption spectra, and infrared (IR) spectra of the metal-free 5,15 -di[4-(5-acetylsulfanylpentyloxy) phenyl]porphyrin H₂[DPP(OC₅H₁₀SCOCH₃)₂] (1) (DPP = 5,15-diphenylporphyrin) and its zinc complex Zn[DPP(OC₅H₁₀SCOCH₃)₂] (2), which exhibit novel structures with two 5-acetylsulfanylpentyloxy side chains at the para-positions of opposite meso-attached phenyl groups. The calculated molecular structure and electronic absorption and IR spectra of 1 and 2 are consistent with the experimental results. The influences of meso-substitution, polar solvents, and central metal substitution on the structure and properties of porphyrin derivatives have been investigated by comparing the corresponding data for 1 and 2 with the help of data for the unsubstituted porphyrin derivatives, namely the metal-free porphyrin H₂Por (3) and the porphyrinato-zinc compound (4). The identities of the main transitions in the electronic absorption spectra of 1 and 2 are assigned and the vibrational modes in their IR spectra are identified with the assistance of animated pictures produced based on normal coordinates. The theoretical work presented here will be helpful in increasing our understanding of the structure and spectroscopic properties, as well as substituent and solvent effects, for these novel porphyrin compounds.     

Synthesis, X-ray structural analysis, and cytotoxic activity of some new androstane d-homo lactone derivatives

A series of d-homo lactones 4?C10 from dehydroepiandrosterone 1 via 16-hydroximino derivatives 2 and 3 were synthesized. The d-homo lactone 4 was transformed by the Oppenauer oxidation to obtain compound 5. The (Z)-2-hydroxymethylene-4-en-3-one compound 6, was obtained through reaction of 4-en-3-one compound 5 with ethyl formate and sodium hydride. The epoxides 8 and 9 were prepared from compound 7 by oxidation with m-chloroperbenzoic acid. Compound 10 was obtained by treating epoxides 8 and 9 with chromium(VI)-oxide. The structure of compounds 6 and 10 were confirmed by X-ray structural analysis. These derivatives were screened for antitumor activity against three tumor cell lines (human breast adenocarcinoma ER+, MCF-7, human breast adenocarcinoma ER?, MDA-MB-231, prostate cancer AR?, PC-3), and one human non-tumor cell line, MRC-5. Compounds 4, 7, 8, and 10 exhibited significant antitumor activity against MDA-MB-231 cells, while compound 5 showed strong cytotoxicity against MDA-MB-231. No compounds displayed toxicity against MRC-5 cells.     

Syntheses, spectroscopic characterization and metal ion binding properties of benzo-15-crown-5 derivatives and their sodium and nickel(II) complexes

New benzo-15-crown-5 derivatives containing nitro, amine and imine groups were prepared. Nitro compound (1) was prepared after the reaction?4′,5′-bis(bromethyl)benzo-15-crown-5 and o-nitrophenol in the presence of NaOH. After reduction process by using hydrazine hydrate and Pd/C amine compound (2) was formed. New crown ether imine compounds (3–5) were synthesized by the condensation of corresponding crown ether diamine (2) with salicylaldehyde derivatives. Sodium complexes of the crown compounds (1a–5a) form crystalline 1:1 (Na⁺: ligand) complexes with sodium perchlorate. Nickel(II) complexes (3b–5b) with 1:1 (Ni²⁺:ligand) stoichiometries were also been synthesized from the Schiff bases (3–5). The results indicated that the Schiff base ligands coordinated through the azomethine nitrogen and phenolic oxygen. The extraction ability of compounds (1, 3, 4 and 5) were also evaluated in chloroform by using several alkali and transition metal picrates such as Li⁺, Na⁺, K⁺, Cr³⁺, Mn²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Pb²⁺.     

1,2,4,5-Tetrahydro-3,2,4-benzothiadiazepin-3,3-dioxide und 1,2,3,5,6,7-Hexahydro-4,3,5-benzothiadiazonin-4,4-dioxide

1.2.4.5-Tetrahydro-3.2.4-benzothiadiazepine-3.3-dioxide (3a) (1 a) was prepared both by treating o-xylylene dibromide with sulfamide and by reaction of o-xylylene diamine (1 c) with SO₂Cl₂ or sulfamide. 4-Chloro-o-xylylene-diamine (2 c) and 1.2-bis(β-aminoethyl)benzene (8), resp., yield 7-chloro-1.2.4.5-tetrahydro-3.2.4-benzothiadiazepine-3.3-dioxide (4 a) and 1.2.3.5.6.7-hexahydro-4.3.5-benzothiadiazonine-4.4-dioxide (9), resp., on treatment with sulfamide. 3 a, 4 a, and9 yield the corresponding N,N′-dialkyl derivatives on treatment of their Na-salts with alkyl halides. Several dialkyl derivatives of3 a were prepared also by reaction of1 a with N,N′-dialkyl sulfamides.     

Design, synthesis, and cytotoxicity of 4-sulfonamide substituted benzamidobenzimidazolones and an acyl benzimidazolone

4-Sulfonamide substituted benzamidobenzimidazolones were designed and docked into the active site model of CDK2, using an oxindole inhibitor as the template. Compounds 6a-6i were then prepared from the reaction of the sulfonyl chloride 1 with different amines to give the corresponding acids (2a-2i), which were converted to their corresponding acyl chlorides (3a-3i). Reaction of 3a-3i with o-nitrophenylhydrazine afforded the respective nitro derivatives (4a-4i). The nitro groups were then reduced to give the corresponding amines (5a-5i), which, upon reaction with ethyl chloroformate, the target compounds (6a-6i) were produced. Target benzimidazolone derivatives (9a-9e) were also prepared from the reaction of isopropenyl benzimidazolone (8) with different sulfonyl or acyl chlorides. The target compounds were then tested by a modified 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay against the cancer cell lines, Hep G2, HT-29, CL1-5 and AGS. Despite similar binding properties of the flexible benzamidobenzimidazolones and rigid cytotoxic oxindole inhibitors at the active site of CDK2, biological screening results indicated that benzamidobenzimidazolones did not exhibit significant cell growth inhibition in vitro. Their analogue, 3-acyl benzimidazolone (12), however, revealed cytotoxicity similar to that of the reference oxindole inhibitor.     

1,3,6-Triphenyl-6-phenylazo-1,4,5,6-tetrahydropyridazin

Base induced 1.4-elimination of pyridine·HI from 1-(2-phenyl-2-phenylhydrazono-ethyl)-pyridinium iodide (6) yields 1.3.6-triphenyl-6-phenylazo-1.4.5.6-tetrahydropyridazine (8) the (4+2)-cyclodimer of the intermediate 1-phenyl-1-phenylazoethylene (7).8 can also be obtained by intramolecular oxidative cyclisation (with KMnO₄) of 1.4-diphenylbutane-1.4-dione bisphenylhydrazone (12). Spectroscopic data (ms,¹H-nmr, uv and ir/Raman) confirm the structure of8.     

Platinum complexes bearing 2,2′-dipyridylamine ligand

The replacement of the iodide ligands in the complex [PtI₂(dpa)] (1) (dpa is 2,2′-dipyridylamine) by silver triflate in acetonitrile afforded the compound [Pt(dpa)(MeCN)₂](SO₃CF₃)₂ (2). Homoleptic complexes [Pt(dpa)₂](X)₂ (3·(X)₂) were synthesized by the treatment of [PtI₂(dpa)] (1) with 2,2′-dipyridylamine in the presence of silver salts AgX in methanol (X = NO₃) or acetonitrile (X = SO₃CF₃). The deprotonation of the complex [3](SO₃CF₃)₂ to give the homoleptic complex [Pt(dpa-H)₂] (4) was performed by two methods, e.g., by the treatment of [3](SO₃CF₃)₂ with 2 equiv. of NaOH in methanol or by the addition of excess Et₃N to a suspension of [3](SO₃CF₃)₂ in methanol. The structures of compounds 1–4 were established by elemental analyses, high resolution electrospray ionization mass spectrometry, IR and NMR spectroscopy; the crystal structure of complexes [2](SO₃CF₃)₂, [3](NO₃)₂·H₂O, [3](SO₃CF₃)₂·2H₂O, and 4 were determined by single-crystal X-ray diffraction.     

Four new dimeric triterpene glucosides from Sanguisorba officinalis

In search for bioactive compounds from the roots of Sanguisorba officinalis L. (Rosaceae), four new dimeric triterpene glucosides, namely sanguidioside A, B, C, and D (1-4) were isolated. Alkaline hydrolysis of 1-2 afforded the corresponding dimeric aglycones (1a and 2a). Meanwhile, a ready intra-molecular transesterification was observed, providing dimeric triterpenes 1b and 2b. Alkaline hydrolysis of the crude dimmeric saponin also provided a new dimeric triterpene, sanguidiogenin (9). The structures of all these compounds are elucidated via spectroscopic and chemical methods, and are further confirmed by the X-ray diffraction analysis of the dimeric aglycone 2a. Compound 3 represents the first dimeric saponin of an oleanolic acid and an ursonic acid derivative, while compound 4 is the first dimeric saponin of oleanolic acid derivatives.     

One-pot microwave-assisted solvent-free synthesis,theoretical and experimental studies on barrier rotation of C–N bond of N-alkenyl-1,2,3-triazoles

The reactions on benzotriazoles continue to happen to reach interesting varieties of their derivatives. This study reports a fast one-pot microwave-assisted solvent-free synthesis of N-alkenyl-1,2,3-benzotriazole (3, 5, and 7) and 1-(2-Alkyloxycarbonyl-vinyl)-1H-[1–3] triazole-4-carboxylic acid methyl ester (8 and 9) derivatives by nucleophilic addition reactions of 1,2,3-benzotriazole (C₆H₅N₃) (1) and 1H-[1–3] triazole-4-carboxylic acid methyl ester (C₄H₄N₃O₂) (1′) with R-propiolates (R = Me, Et; 2 & 4) and phenylacetylene 6 in good yields. The values of activation energy for rotation around C–N bond in the synthesized N-alkenyl-1,2,3-triazole compounds were studied by DFT-B3LYP/6-31G* method.     

Crystal and molecular structure of two new Schiff bases: Paeonol-ethylenediamine and paeonol-1,3-propylenediamine

Two new Schiff bases were prepared by the condensation reaction of paeonol with ethylenediamine (for compound 1) and 1,3-propylenediamine (for compound 2). The compounds were studied with single crystal X-ray diffraction method. Compound 1 is monoclinic, space group P2₁/c, a = 10.956(15) Å, b = 6.767(10) Å, c = 12.494(18) Å; β = 104.66(2)°, V = 896(2) ų, Z = 2. Compound 2 is triclinic, space group P-1, a = 6.878(2) Å, b = 12.141(4) Å, c = 12.414(4) Å; α = 101.023(6)°, β = 103.415(6)°, γ = 102.337(6)°, V = 952.8(6) ų, Z = 2. The molecular structures of 1 and 2 are similar; the molecule being centrosymmetric in 1 but asymmetric in 2.     

Lanthanide Cluster Organic Frameworks Derived from Pyridine-2,6-dicarboxylate and Oxalate: Syntheses,Structures and Luminescence

Two novel cluster organic frameworks derived from pyridine-2,6-dicarboxylate (PDA) and oxalate (ox^2?) have been hydrothermally made: [Eu₃(SO₄)(PDA)₃(ox)_0.5(H₂O)₅]·4H₂O (1) and Er(PDA)(ox)_0.5(H₂O) (2). Compound 1 possesses one-dimensional chain structure constructed from the alternate linkage of tetranuclear [Eu₄(SO₄)₂]⁸⁺ (Eu₄) and dinuclear [Eu₂(ox)]⁴⁺ (Eu₂) clusters. Compound 2 is a two-dimensional layer based on dimeric [Er₂(COO)₂]²⁺ (Er₂) cluster units. Interestingly, such layer can be intuitively viewed as the linkages of helical chains and oxalate. In these two compounds, all anions are bivalent, and the ratio of trivalent lanthanide ions to these dianions is 2:3. Furthermore, compound 1 exhibits strong red luminescence upon 276 nm excitation.