Electrochemical reduction of dehydroamino acids: synthesis and photophysical properties of β,β-diarylalanines

Several β,β-disubstituted dehydroalanines were prepared from β,β-dibromo or β-bromo, β-substituted dehydroalanines and aryl boronic acids using a Suzuki-Miyaura cross-coupling reaction. The electrochemical behaviour of these compounds was studied by cyclic voltammetry. All compounds studied showed similar reduction potentials and these were similar to the peak potential of the methyl ester of N-tert-butoxycarbonyl dehydrophenylalanine. Thus, the presence of a second aryl moiety in the dehydroalanine scaffold does not significantly change the reduction potential.Controlled potential electrolyses were performed at the cathodic peak potential in the presence of triethylammonium chloride as proton donor. The only products isolated in good to high yields were the corresponding β,β-diarylalanines. This reaction was also carried out using a dipeptide containing a β,β-diaryldehydroalanine to give a 1:1 diastereomeric mixture of the reduction product.The photophysical properties of two of the β,β-diaryldehydroalanines and of the corresponding β,β-diarylalanines were studied in three solvents of different polarity. The β,β-diaryldehydroalanines show low fluorescent quantum yields (Φ_F<9%) due to the conjugation of the aromatic moieties with the α,β-double bond and with the carbonyl group, which favours the non-radiative deactivation pathways. The absence of conjugation in the reduction products leads to a significant increase in the fluorescence quantum yields. These results show that the β,β-disubstituted alanines could be used as fluorescent markers.     

Star-shaped triphenylamine terminated difluoroboron β-diketonate complexes: synthesis,photophysical and electrochemical properties

Two new star-shaped difluoroboron β-diketonate complexes (TBC)₃Ph and (TBF)₃Ph, in which the terminal groups of triphenylamine functionalized difluoroboron β-diketonates were bridged by carbazole or fluorene to the core of 1,3,5-benzene, have been synthesized. It was found that they gave high molar extinction coefficients, meaning strong light-harvesting ability, and emitted intense yellow light with fluorescence quantum yields (Φ_F) of 0.73 and 0.67 for (TBC)₃Ph and (TBF)₃Ph, respectively, in toluene as well as red light in solid states with Φ_F of 0.36 and 0.27, respectively. The electrochemical behaviors suggested that they had considerably higher electron affinities than tris(8-hydroxyquinoline)aluminum (AlQ₃), which indicated that they could be used as electron-transporting materials besides emitting materials.     

Case synthesis of a β-chloro bulky bis-pocket corrole: Crystallographic characterization and photophysical properties

A new bulky 2-chloro-5,10,15-tris(2,4,6-triphenylphenyl)-corrole was casually synthesized and the effect of mono-β-chlorination on its photophysical, electrochemical properties and light-induced singlet oxygen generation was investigated.     

Synthesis and photophysical evaluations of β-fused uracil-porphyrin derivatives

New β-fused uracil-porphyrin conjugates were synthesized by the tetramerization of uracil-pyrroles under acidic conditions. Two different synthetic approaches were systematically studied in order to evaluate their efficiency, as well as the possibility to obtain a single regioisomer. Metallation effects were studied for aggregation in solution, and preliminary photophysical experiments were also performed in order to evaluate the potential of these new compounds.     

Synthesis, electrochemical and photophysical properties of β-carboxy triaryl corroles

An unswerving one-pot conversion of 3-formyl-5,10,15-triaryl substituted corroles and their copper(III) derivatives to the corresponding 3-carboxy-5,10,15-triaryl substituted corroles was achieved by adopting mild reaction conditions by using hydroxylamine hydrochloride and phthalic anhydride. All these substituted carboxy corroles were completely characterized by using Mass, CHN analysis, IR, ¹H NMR, UV-vis., Fluorescence spectroscopies, and cyclic voltammetry. Both the absorption maxima and emission maxima of carboxy corroles were red shifted by 5-13 nm. The LUMO level of these corroles is above the TiO₂ conduction band and HOMO level was below the redox electrolytes. These β-carboxy corroles confined with may find applications as sensitizers in dye-sensitized solar cells.     

The pyridazine–tetrathiafulvalene conjugates: synthesis,photophysical, and electrochemical properties

To study the electronic interactions in donor–acceptor (D–A) conjugates as a precursor of optoelectronic materials, a series monopyridazine-annulated tetrathiafulvalenes and a bispyridazine-annulated tetrathiafluvalene were synthesized by a condensation reaction of 2,3-dimethoxycarbonyl-6,7-dibutylthiotetrathiafulvalene or/and 2,3,6,7-tetramethoxycarbonyltetrathiafulvalene with hydrazine hydrate and structurally characterized by conventional chemical and physical methods. Their electronic properties have been studied experimentally by the combination of electrochemistry and UV–vis spectroscopy. All of monopyridazine-tetrathiafulvalene conjugates 7–13 show intramolecular charge transfer interaction in ground states, which is rationalized on the basis of density functional theory. Their HOMO energy levels and E_g^opt values were estimated to be ?4.88 to ?5.07 eV from cyclic voltammetry and 2.43–2.79 eV from the absorption spectra, respectively. The X-ray crystallographic analyses of the pyridazine–tetrathiafulvalene conjugates 7, 11–13 are also reported.     

Study on molecular and electronic structures, and spectroscopic properties of azide ruthenium complexes with pyridine and β-picoline ligands

The [Ru(N₃)₂(PPh₃)(py)₃] and [Ru(N₃)₂(PPh₃)₂(β-pic)₂] complexes have been prepared and studied by IR, NMR, UV-Vis spectroscopy and X-ray crystallography. The complexes were prepared in the reactions of [RuCl₂(PPh₃)₃] with pyridine, β-picoline and NaN₃ in methanol solutions. The electronic structures of the obtained complexes have been calculated using the DFT/TD-DFT method. The trans effect of triphenylphosphine on the pyridine molecule has been studied using NBO and molecular orbital terms, and impact of the acceptor properties of the halide/pseudohalide co-ligands was indicated.     

Synthesis,structure, photophysical,and electrochemical properties of donor–acceptor ferrocenyl derivatives

A series of donor–acceptor compounds 2–6 have been synthesized, via Knoevenagel condensation reaction (using conventional method, as well as microwave method). The ferrocene unit acts as a donor, conjugated phenyl–acetylene linker act as a π-electron relay unit, and malononitrile, cyanoacetic acid, and indanone groups act as acceptor. The electronic absorption spectra displayed a broad intramolecular charge transfer (CT) band in the visible region (450–650 nm). The electrochemical studies suggest considerable donor–acceptor interaction. The single crystal X-ray structure of 2, and 3 are reported, the structure reveals that 2 is nearly planar compared to 3. The supramolecular structure of 2 exhibits intramolecular C–H–π, and C–H–N interaction, which leads to formation of 2D network, whereas compound 3 shows head to tail dimer formation through C–H–π, and π–π interaction.     

Highly emissive hand-shaped π-conjugated alkynylpyrenes: synthesis, structures, and photophysical properties

Three alkynyl-functionalised, hand-shaped, highly fluorescent and stable emitters, namely, 2-tert-butyl-4,5,7,9,10-pentakis(p-R-phenylethynyl)pyrenes have been successfully synthesized via a Pd/Cu-catalysed Sonogashira cross-coupling reaction. The chemical structures of the alkynylpyrenes were fully characterized by their (1)H/(13)C NMR spectra, mass spectroscopy and elemental analysis. Synchrotron single-crystal X-ray analysis revealed that there is a 1-D, slipped, face-to-face motif with off-set, head-to-tail stacked columns, which are clearly influenced by the single, bulky, tert-butyl group in the pyrene ring at the 2-position. Detailed studies on the photophysical properties in both solutions and thin films strongly indicate that they might be promising candidates for optoelectronic applications, such as organic light-emitting devices (OLEDs) or as models for investigating the fluorescent structure-property relationship of the alkynyl-functionalised pyrene derivatives.     

Synthesis and photophysical properties of some 6,6″-functionalized terpyridine derivatives

The synthesis and photophysical properties of several 6,6″ symmetrically substituted 4′-aryl-2,2′:6′,2″-terpyridine derivatives are reported herein. The UV-Vis spectra in acetonitrile as well as in dichloromethane show two intense bands in the UV areas 252–262 nm and 275–290 nm while the fluorescence emission spectra are only slightly influenced by chemical derivatization.     

Synthesis and photophysical properties of europium pentafluorinated β-diketonate complexes

Research on Chemical Intermediates - Two pentafluorinated β-diketone ligands, 4,4,5,5,5-pentafluoro-1-(4-methoxyphenyl)pentane-1,3-dione (PFMP) and 4,4,5,5,5-pentafluoro-1-(4-dimethyl...     

Synthesis of β-aroylvinyl derivatives of triphenylphosphine and pyridine based on β-aroylacrylic acids

Bromination of β-aroylacrylic acids afforded β-aroyl-α,β-dibromopropionic acids. The latter reacted with pyridine to form 1-(β-aroylvinyl)pyridinium bromides. Reaction of the salts obtained with triphenylphosphine resulted in β-aroylvinyltriphenylphosphonium bromides.     

Donor–acceptor perylenediimide–ferrocene conjugates: synthesis,photophysical, and electrochemical properties

Donor–acceptor, perylenediimide–ferrocene conjugates have been synthesized by Suzuki, and Sonogashira coupling reactions. The photophysical and electrochemical properties of these conjugates are discussed. It has been shown that fluorescence as well as the electron affinity of the perylenediimide can be tuned by attaching the appropriate ferrocenyl derivatives.     

Di- and trinuclear Ru(II) complexes of 1,10-phenanthroline and 2,2′-bipyridine derivatives; synthesis,photophysical and electrochemical properties

Three heterotopic ligands L¹, L², and L³ based on 1,10-phenanthroline and 2,2′-bipyridine moieties have been synthesized and characterized. The Ru(II) complexes [{Ru(bpy)₂}₃(µ₃-L¹)](PF₆)₆, [{Ru(bpy)₂}₃(µ₃-L²)](PF₆)₆, and [{Ru(bpy)₂}₂(µ₂-L³)](PF₆)₄ (bpy = 2,2′-bipyridine) have been prepared by refluxing Ru(bpy)₂Cl₂·2H₂O with each ligand in ethanol. All three complexes display MLCT absorptions at around 455 nm and emissions at around 618 nm. Electrochemical studies of the complexes reveal one Ru(II)-centered quasi-reversible oxidation at around 1.32 V and three ligand-centered reductions in each case.     

Cyclopropanation of 1,2-dibromoethylphosphonate: a synthesis of β-aminocyclopropylphosphonic acid and derivatives

Diethyl (1,2-dibromoethyl)phosphonate was found to undergo cyclopropanation with nitromethane in good yield. The resulting trans β-nitrocyclopropylphosphonate was converted to the trans N-protected aminocyclopropylphosphonate through a reduction–protection sequence. Subsequent hydrolysis gave the free β-aminocyclopropylphosphonic acid without any formation of ring-opening byproduct. Cyclopropanation of 1,2-dibromoethylphosphonates with nitroalkanes and their reduction are also discussed.     

Ph₂N-susbtituted ethylene-bridged p-phenylene oligomers: synthesis and photophysical and redox properties

For a series of p-phenylene-based oligomers terminated with two triphenylamines, their absorption, photoluminescence, and band gaps show a pattern of extensive π-conjugation with increasing array size. Oligomers with large central arrays have greater quantum yields than their small analogues. Cyclic voltammetric (CV) measurements indicated two-step oxidations of the two diphenylamino groups for compounds 1-5 and one-step oxidations for the two amines of large oligomers 6 and 7.     

Efficient synthesis of β-halogeno protected l-alanines and their β-phosphonium derivatives

Ring opening of oxazolines, prepared from l-serinates, with trimethylsilyl halides (TMSX) led to β-halogeno-N-benzoyl-α-amino esters in good to excellent yields. Quaternization of triphenylphosphine by the β-bromo or -iodo amino esters gave the corresponding β-phosphonium salts in overall yields of up to 93% and with e.e. >96%. Hydrolysis of the ester function afforded the phosphonium salt bearing an N-benzoyl-α-amino acid substituent, with partial racemization. However, the reaction of the TMSX with the carboxylic salt, prepared by saponification of the starting oxazoline ester, furnished the corresponding β-halogeno-N-benzoyl-α-amino acids in 70–95% yields. Quaternization of triphenylphosphine by the bromo or iodo derivatives led to the phosphonium salts bearing a free acid function in 95% yield, without racemization. The efficiency of this synthesis was demonstrated by the preparation of these phosphonium salts in excellent overall yields, by a one-pot procedure starting from the oxazoline.     

synthesis and properties of β-brominated metal complexes of meso-triphenylcorrole

Spectral properties and chemical stability of Mn(III), Mn(IV), Fe(III), Fe(IV), and Cu(III) complexes of β-octabromotriphenylcorrole [(β-Br)₈(ms-Ph)₃Cor], synthesized from β-unsubstituted compounds by their reaction with molecular bromine, were studied. Cyclic voltammetry, electron microscopy, and X-ray spectral microanalysis were used to obtain electrochemical characteristics of metal corroles M(β-Br)₈(ms-Ph)₃Cor and gain insight into the surface texture of active catalysts on the basis of metal corroles. The electron-acceptor β-bromine substitution in the MCor macrocycle shifts the equilibrium in electron-donor solvents to lower oxidation states of the metals and also stabilizes manganese and destabilizes copper complexes in the protondonor medium HOAc-H₂SO₄. The electrocatalytic activity of the complexes in the reduction of molecular oxygen depends on the nature of the ligand and increases in the order Mn ≤ Cu ? Fe in the case of β-octabrominated macrocycles. The character of distribution of active centers on the surface of the catalysts was established for the first time.     

Rational synthesis and X-ray structural study of manganese–pyridine–alcohol derivatives

Systematic syntheses of manganese derivatives with 2-pyridineethanol, 2-pyridinemethanol and 2,6-pyridinedimethanol as chelating ligands have been undertaken to produce [trans-Mn(C₅H₄N-2-CH₂CH₂OH)₂Cl₂] (1), [cis-Mn₂(μ-Cl)₂(Cl)₂(C₅H₄N-2-CH₂CH₂OH)₂(OH₂)₂] (2), [cis-Mn₂(μ-Cl)₂(C₅H₄N-2-CH₂OH)₄]Cl₂ (3) and [MnCl{η₃-C₅H₃N-2,6-(CH₂OH)₂}{η₂-(C₅H₃N-2,6-(CH₂OH)₂)}]Cl (4). The complexes were characterized by single-crystal X-ray diffraction. The oxidation state of the manganese ions in these complexes is 2+. Magnetic data are measured down to 2?K; in dimer complexes (2 and 3) a significant antiferromagnetic interaction is observed between two manganese ions.     

Synthesis of pyridine derivatives by the three-component condensation of a β-dicarbonyl compound, β-enaminocarbonyl compound, and ethyl orthoformate

The major products of the three-component condensation of a -dicarbonyl compound, -enaminocarbonyl compound, and ethyl orthoformate are pyridine derivatives. The reaction of 1,3-cyclohexanedione or dimedone, the enamino ketones obtained from these diones, and ethyl orthoformate gives octahydroacridinediones, while the reaction of dimedone, ethyl -aminocrotonate, and ethyl orthoformate gives a tetrahydroquinoline derivative. The structures of the minor products were established in some cases. The reduction of 3,3,6,6-tetramethyl-1,2,3,4,5,6,7,8-octahydro-1,8-acridinedione by LiAlH₄ proceeds with retention of the pyridine ring and leads to the corresponding octahydroacridinediol.Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, 220141 Minsk, Belarus Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 774–781, June, 1999.