Competitive decay pathways of the radical ions formed by photoinduced electron transfer between quinones and 4,4'-dimethoxydiphenylmethane in acetonitrile

The reactivity of the cation radical of (4-MeOC6H4)2CH2 photosensitized by 1,4-benzoquinone (BQ), 2,5-dichloro-1,4-benzoquinone (Cl2BQ), and tetrachloro-1,4-benzoquinone (chloranil, CA) was investigated in acetonitrile. The main photoreaction products obtained by steady-state irradiation were identified to be: (4-MeOC6H4)2-CHOC6H4OH, sensitized by BQ; (4-MeOC6H4)2CHCl, sensitized by Cl2BQ; (4-MeOC6H4)2CHOH, sensitized by CA. The mechanism of their formation was investigated by nanosecond laser flash photolysis that allowed transient species (radical ions, neutral radicals, and ions) to be detected and characterized in terms of absorption spectra, formation quantum yields, and decay rate constants. For all systems, the interaction between the triplet quinone (Q) and (4-MeOC6H4)2CH2 produced the corresponding radical ions (quantum yield phi > or = 0.72) which mainly decay by back electron transfer processes. Less efficient reaction routes for the radical ions Q*- and (4-MeOC6H4)2CH2*+ were also: i) the proton-transfer process with the formation of the radical (4-MeOC6H4)2CH* by use of Cl2BQ; ii) the hydrogen-transfer process with the formation of the cation (4-MeOC6H4)2CH+ in the case of CA. Instead. BQ sensitized a much higher yield of BOH* and (4-MeOC6H4)2CH*, mainly by the direct interaction of triplet BQ with (4-MeOC6H4)2CH2. It was also shown that the presence of salts decreases significantly the rate of the back electron transfer process and enhances the quantum yields of formation of the neutral radicals and ions when Cl2BQ and CA are used, respectively. The behavior of BQ*-, Cl2BQ*-, and CA*- appears to be mainly determined by the Mulliken charges on the oxygen atom obtained from quantum mechanical calculations with the model B3LYP/6-311G(d,p). Spin densities seem to be much less important.     

Synthesis,electrochemistry and IR spectroelectrochemistry of bisferrocenyl bridged benzene derivates

Two novel biferrocenylcarboxylate benzene derivatives, namely, 1,4-bis(2-Ferrocenecarboxylate) benzene (Fc₂B) and 1,4-bis(2-Ferrocenecarboxylate)-2′-methylbenzene (Fc₂M), have been synthesized. The as-prepared complexes have been confirmed by IR, ¹H NMR and MS. The electron transfer mechanisms of the two compounds and the other three bisferrocenyl bridged benzene complexes, 1,4-disferrocenyl benzene (Fc₂P), 1,4-bis(2-ferrocenylvinyl) benzene (Fc₂E), and 1,4-bis(2-ferrocenylacetyleneyl) benzene (Fc₂Q), have been studied by cyclic voltammetry (CV), in situ difference FT-IR (SNFTIR), and rapid-scan time-resolved FT-IR spectroelectrochemistry (RS-TRS FT-IR). The CV results suggest that the redox formal potentials of the five bridged complexes are depended on their bridged groups and abilities of withdrawing electron. IR absorption peaks arisen from intermediate appearance and disappearance in the oxidation and reduction process of Fc₂B, Fc₂E, Fc₂P and Fc₂Q were clearly observed by the in situ rapid-scan or SNFTIR spectroelectrochemistry. The results indicated the redox process of the four bisferrocenyl bridged benzene complexes involved two consecutive one-electron steps. Although the intermediate peak of Fc₂M was not observed by in situ FT-IR spectroelectrochemistry, we still thought the redox process of Fc₂M could involve two consecutive one-electron steps.     

Syntheses, structures, and anion-binding properties of two novel calix[2]benzo[4]pyrroles

Calix[2]benzo[4]pyrrole m-6 and p-6, each containing two dipyrromethane moieties and two m-phenylene or p-phenylene units, respectively, were readily synthesised from pyrrole, 1,3- and 1,4-bis(1,1'-dimethylhydroxymethyl)benzene, (m-4 and p-4, respectively) and acetone. Macrocycles m-6 and p-6 were tested as receptors for a selection of anions, such as acetate, dihydrogenphosphate and fluoride. The X-ray structures of m-6 and p-6 and those of the complexes m-6F(-), m-6Cl(-) and m-6CH(3)COO(-) (with an nBu(4)N(+) counterion) were also determined.     

The structure dependent electrochemical-response of novel 1-(4-mercaptobutyl)-4-(2-ferrocenylvinyl)pyridinium bromide SAMs on an au electrode

The 1-(4-mercaptobutyl)-4-(2-ferrocenylvinyl)pyridinium bromide (1-HS(CH2)(4)-4-[(E)-FcCH=CH]C5H4N)+Br- and its hydrogenated product [1-HS(CH2)(4)-4-(-FcCH2CH2)C5H4N]+Br- were synthesized and assembled on an Au electrode to form self-assembled monolayers which showed a structure-dependent electrochemical-response in phosphate buffer aqueous solutions (pH = 7).     

New Dimethyl(Methylenoxyaryl)Phosphine Oxides

Abstract

In the poster presentation is reported the preparation of the new dimethyl(methylenoxyaryl)phosphine oxides via ZVilliamson reaction from dimethyl-chloromethyl-phoaphine oxide and sodium solts of the coresponding phenols: l-di-methylphosphinylmethylenoxy-4-methyl-2,6-bis(l,l -dimethylethyl)benzene; 1,3-bis(dimethylphosphinylmethylenOxy)benzene; 1,4-bis(dimethylphosphinylmethylenoxy)ben-zene; 1,3,5-tris(dimethylphosphinylmethylenoxy)benzene; 1,2,3-tris(dimethylphosphinylmethylenoxy～benzene; 2,2′-methylene-bia(6-tert-butyl-4-methyl-l-dimethyl-phosphinylmethylenoxybenzene); 2,2′-rnethylene-bis-(6-tert-butyl-4-ethyl-l-dimethylphosphinylmethyleno～-benzene) and 1,1,3-tris(5-tert-butyl-4-dimethylphoa-phinylmethylenoxy-2-methyl-phenyl)butan.     

Photoreduction of p-benzoquinones: effects of alcohols and amines on the intermediates and reactivities in solutions

The photochemistry of 1,4-benzoquinone (BQ) and alkyl-, Cl- and related derivatives, e.g. methyl-, 2,6-dimethyl-, chloro-, 2,5-dichloro-1,4-benzoquinone, duroquinone and chloranil, was studied in nonaqueous solvents by UV-vis spectroscopy using nanosecond laser pulses at 308 nm. The reactivity of the triplet state (3Q*) of the quinones with 2-propanol in the absence of water is largest for BQ and depends mainly on the quinone structure, whereas the rate constant of electron transfer from amines, such as triethylamine (TEA) or 1,4-diazabicyclo[2.2.2]octane, is close to the diffusion-controlled limit for BQ and most derivatives. Photoinduced charge separation after electron transfer from amines to 3Q* and the subsequent charge recombination or neutralization are supported by time-resolved conductivity measurements. The half-life of the decay kinetics of the semiquinone radical (*QH/Q*-) depends significantly on the donor and the medium. The photoconversion into the hydroquinones was measured under various conditions, the quantum yield, lambda(irr) = 254 nm, increases with increasing 2-propanol and TEA concentrations. The effects of quenching of 3Q*, the *QH/Q*- radicals and the photoconversion are outlined. The mechanisms of photoreduction of quinones in acetonitrile by 2-propanol are compared with those by TEA in benzene and acetonitrile, and the specific properties of substitution are discussed.     

New type of quinone-quinone complexation in the reaction of 2,5-dichloro-1,4-benzoquinone with morpholine at high pressure

The complex of tetralcis(morpholino)-1,4-benzoquinone with 2,5-bis(morpholino)-1,4-benzoquinone of 2 : 1 stoichiometry was obtained in 9 % yield in the reaction of 2,5-dichloro-1,4-benzoquinone with morpholine at high pressure.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 488–490, February, 1996     

Electrochemical and spectral properties of thienylene-polyparaphenylenevinylene derivative stereoisomers

Four new compounds: 1,4-dimetoxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene), 1,4-dietoxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene), 1,4-isopropyloxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene) and 1,4-dietoksy-2,5-bis[2-(5-methylthiophen-2-yl)ethenyl]benzene are synthesized. Three steroisomers ZZ, EZ and EE are isolated from the reaction mixture for the first two of them. Third compound is fully converted to the most stable EE form. Polymerization of all isomers leads to identical polymeric product. Mechanism of polymerization is recognized by using model molecule with methyl substituents blocking α-, α′-sites. All seven stereoisomers have photoluminescent properties. Detailed spectral and electrochemical studies reveal isomerization phenomena during oxidation or at light exposure. Published in Russian in Elektrekhimiya, 2006, Vol. 42, No. 12, pp. 1401–1408. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes.” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Gas-chromatographic separation of silicon-containing sterically hindered phenols and their oxidation products

Conclusions It was shown to be possible to separate and isolate in pure form 2,6-bis(trimethylsilyl)-4-terbutylphenol, 2,4-diterbutyl-6-trimethylsilylphenol, substituted bis(siloxy)diphenyls, and the compounds (obtained for the first time) 2,6-bis(trimethylsilyl)-1,4-benzoquinone and 2-terbutyl-6-trimethylsilyl-1,4-benzoquinone by gas-liquid chromatography.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 686–687, March, 1970.     

Oxygen uptake upon photolysis of 1,4-benzoquinones and 1,4-naphthoquinones in air-saturated aqueous solution in the presence of formate, amines, ascorbic acid, and alcohols

The effects of oxygen in the photoreduction of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), and a series of derivatives were studied in aqueous solution in the presence of acetonitrile and formate, aliphatic amines, e.g., EDTA or triethylamine, ascorbic acid, and alcohols, e.g., methanol or 2-propanol. The quinone triplet state is quenched, whereby the semiquinone and donor radicals are formed which react subsequently with oxygen. The overall reaction is oxidation of the donors and conversion of oxygen via the hydroperoxyl/superoxide radical into hydrogen peroxide. The quantum yield (Phi-O2) of this oxygen uptake changes in 2-propanol-water (1:10) from <0.01 for BQ to Phi-O2 = 0.5-0.8 for NQ. Generally Phi-O2 increases with increasing donor concentration. The specific properties of quinone structure, the radical equilibria and reactivity, and the concentration dependences are discussed.     

水溶性的反式-二苯二乙烯基苯型非线性光学材料的合成

由3，4，5-三羟基苯甲酸甲酯经烷基化、还原、氧化和高度立体选择性的 Wadsworth-Emmons反应，合成了两个带六条烷氧基长链的水溶性的反式-二苯二乙 烯基苯(1a)和(1b)，经~1H NMR、MS及元素分析确证其结构。     

Two-photon photosensitized production of singlet oxygen: optical and optoacoustic characterization of absolute two-photon absorption cross sections for standard sensitizers in different solvents

Singlet molecular oxygen, O2(a1Deltag), can be produced upon resonant two-photon excitation of a photosensitizer. In the present study, two molecules that have received recent attention in studies of nonlinear organic materials were characterized for use as standard two-photon sensitizers: 2,5-dicyano-1,4-bis(2-(4-diphenylaminophenyl)vinyl)-benzene, CNPhVB, and 2,5-dibromo-1,4-bis(2-(4-diphenylaminophenyl)vinyl)-benzene, BrPhVB. Absolute two-photon absorption cross sections, delta, were independently determined for these molecules using two techniques that have heretofore not been applied to this problem: an optical technique (time-resolved detection of O2(a1Deltag) phosphorescence) and a nonoptical technique (a time-resolved laser-induced optoacoustic experiment). For experiments performed in toluene, a solvent commonly used for such nonlinear optical studies, appreciable absorption by the solvent itself complicates the measurements. In cyclohexane, however, delta values could be obtained without the interfering effects of solvent absorption. On the basis of these results, we discuss key aspects of the respective techniques used to quantify values of delta. The information reported herein provides some explanation for the lack of consensus that is routinely observed in published values of delta, certainly for experiments performed in aromatic solvents such as toluene and benzene.     

A convenient synthesis and spectroscopic characterization of N, N'-Bis(2-propenyl)-2,7-diazapyrenium quaternary salts

N,N'-Bis(2-propenyl)-2,7-diazapyrenium salts are synthesized in good yield from the reaction of 1,4,5,8-naphthalenetetracarboxylic dianhydride with allylamine, followed by LiAlH(4) reduction and subsequent oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The nature of the counteranion depends on the solvent system used for recrystallization of the crude product from the final DDQ-oxidation step. X-ray analysis shows that if recrystallization is carried out in boiling CH(3)OH/H(2)O (1:1, v/v), the counteranion in the resulting deep-red crystals is always the alkoxy anion of 2-cyano-5,6-dichloro-3-hydroxy-1,4-benzoquinone, whether the final DDQ oxidation ends with addition of HClO(4) or HCl; on the other hand, if recrystallization is carried out with anhydrous acetonitrile, the product is N,N'-bis(2-propenyl)-2,7-diazapyrenium diperchlorate or dichloride depending on whether the DDQ oxidation is followed by addition of concd HClO(4) or concd HCl, respectively. Importantly, if the DDQ oxidation is quenched with HBr, Br(-) is oxidized to Br(2) by unreacted DDQ, and the resulting product is N, N'-bis(2,3-dibromopropyl)-2,7-diazapyrenium dibromide. Comparative absorption and time-resolved emission studies provide evidence for possible dimerization of N,N'-bis(2-propenyl)-2,7-diazapyrenium diperchlorate in CH(3)CN.     

几种荧光有机化合物的电荷转移光谱

具有荧光的有机化合物是一些具有多个共轭双键,分子呈平面结构,有大的电子离域体系的化合物.     

Iron pentacarbonyl assisted photochemical route to 2,5- and 2,6-divinyl-substituted 1,4-benzoquinones from 1-ene-3-ynes

Photochemical reaction between the enynes, (Z)-1-methoxybut-1-ene-3-yne, 1 or isopropenyl acetylene, 2 with CO in presence of Fe(CO)₅ yields the 2,6- and 2,5-divinyl-substituted 1,4-benzoquinones: 2,6-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (3, 42%), 2,5-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (4, 31.5%), [{η²,η²:2,6-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (5, 45%), and {η²,η²:2,5-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (6, 65%).     

Reactions of 1,4-bis(tetrazole)benzenes: formation of long chain alkyl halides

The reactions of 1,4-bis[2-(tributylstannyl)tetrazol-5-yl]benzene with α,ω-dibromoalkanes were carried out in order to synthesise pendant alkyl halide derivatives of the parent bis-tetrazole. This led to the formation of several alkyl halide derivatives, substituted variously at N1 or N2 on the tetrazole ring. The crystal structures of 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (2-N,2-N′), 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (1-N,2-N′) and 1,4-bis[(2-(8-bromooctyl)tetrazol-5-yl)]benzene (2-N,2-N′) are reported. Further discussion involves the structure of 1,4-bis[2-(6-bromohexyl)-2H-tetrazol-5-yl]benzene (2-N,2-N′) previously reported.     

Syntheses and phosphorescent properties of blue emissive iridium complexes with tridentate pyrazolyl ligands

Novel neutral mixed-ligand Ir(N=C=N)(N=C)X complexes (N=C=N = 1,3-bis(3-methylpyrazolyl)benzene (bpzb), 1,5-dimethyl-2,4-bis(3-methylpyrazolyl)benzene (dmbpzb), and 1,5-difluoro-2,4-bis(3-methylpyrazolyl)benzene (dfbpzb); N=C = 2-phenyl pyridine (ppy); and X = Cl or CN) have been synthesized and characterized. An X-ray single-crystal structure of the complex Ir(dmbpzb)(ppy)Cl shows that the nitrogen atom in the ppy ligand occupied the trans position to the carbon atom in the tridentate N=C=N ligand of dmbpzb with the Ir-C bond length of 1.94(1) A, whereas the coordinating carbon atom occupied the trans position of chlorine. Electrochemical data show that the complexes exhibit an oxidation Ir(III/IV) process in the potential range of +0.5 approximately 0.9 V and two irreversible reductions at approximately -2.6 and -3.0 V against Fc (0)/Fc (+), respectively. All of the Ir(III) complexes do not emit phosphorescence at room temperature, although strong phosphorescence is exhibited at 77 K with the 0-0 transition centered at around 450 nm and lifetimes of 3-14 mus. DFT calculations indicate that the HOMOs are mainly localized on iridium 5dpi and chlorine ppi*, whereas the LUMOs are mainly from the ppy ligand pi* orbitals. The phosphorescence originates from a (3)LC state mixed with the (3)MLCT and (3)XLCT ones. Temperature-dependent lifetime measurements of Ir(dfbpzb)(ppy)Cl reveal the existence of a thermal deactivation process with a low activation energy (1720 cm (-1)) and very high frequency factor (2.3 x 10 (13) s (-1)). An unrestricted density functional theory indicates that the dd state, in which both the Ir-N (pyrazolyl) bond lengths increase considerably, exists almost at the same energy as that for the phosphorescent state. A thorough analysis based on the potential energy surfaces for the T 1 and S 0 states allows us to determine the reaction pathway responsible for this thermal deactivation. The calculated activation energies of 1600 approximately 1800 cm (-1) are in excellent agreement with the observed values.     

Synthesis of benzoquinone derivatives containing benzotriazole fragments

2,3,5,6-Tetrakis(1H-benzotriazol-1-yl)-1,4-benzoquinone was synthesized in 85% yield by reaction of 2,3,5,6-tetrachloro-1,4-benzoquinone with 1H-benzotriazole in pyridine at room temperature. Treatment of 2,3,5,6-tetrakis(1H-benzotriazol-1-yl)-1,4-benzoquinone with piperidine, ω-amino acids, and aromatic amines gave the corresponding 2,5-diamino-3,6-bis(1H-benzotriazol-1-yl)-1,4-benzoquinones.     

Stereoselective tandem 1,4-addition reactions for benzenes: a comparison of Os(II), Re(I), and W(0) systems

The arene ligand in the complex TpRe(CO)(MeIm)(eta2-benzene) (Tp = hydridotris(pyrazolyl)borate; MeIm = N-methylimidazole) undergoes tandem electrophile/nucleophile 1,4-addition reactions. Subsequent oxidative demetalation affords cis-3,6-disubstituted 1,4-cyclohexadienes (46-84%). Common organic electrophiles such as acetals and Michael acceptors were successfully added to the bound benzene to generate eta3-benzenium complexes, which then were treated with a silyl ketene acetal, silyl vinyl ether, phenyllithium, or malonate ester to afford 1,4-dialkylated dihydrobenzene complexes. The d6 transition metal analogues TpW(NO)(PMe3)(eta2-benzene) and [Os(NH3)5(eta2-benzene)]2+ also undergo 1,4-dialkylation reactions, and the relative ability of all three metals to activate arenes is compared.     

Metallopolymers featuring boratabenzene iron complexes

Boratabenzene-derived metallocene analogues are introduced as versatile new building blocks for metallopolymers. Bis(borinato)iron(II) complexes of the type Fe(C(5)H(5)B-R)(2) (R: C≡CH, C≡CSiMe(3), 4-(1-benzyl-1,2,3-triazolyl) were synthesized and spectroscopically, structurally, and electrochemically characterized. Polymerization via Sonogashira-Hagihara coupling of the alkynyl-substituted derivative Fe(C(5)H(5)B-C≡CH)(2) with 2,5-bis(dodecyloxy)-1,4-diiodobenzene yields a film-forming polymer in 50-69% yield. Polymer batches were obtained with number-average molecular weights (M(n)) of 11.7 and 20.5 kDa and polydispersity indices (PDI) of 1.55 and 2.65, respectively, as determined by gel permeation chromatography relative to polystyrene standards. Click-type polymerization of Fe(C(5)H(5)B-C≡CH)(2) through azide-alkyne cycloaddition with 1,4-bis(4-azidobutoxy)benzene gives the corresponding metallopolymer with an M(n) of 5.7 kDa and a PDI of 2.29 in 87% yield.