Showing papers on "Substituent published in 2007"

Fluorinated liquid crystals – properties and applications

Abstract: This critical review begins with a brief, but essential, introduction to the special nature of liquid crystal materials, their peculiar properties, and their commercial applications, followed by an introductory insight into the remarkable nature of the fluoro substituent, and its fascinating influence on the properties of organic compounds. However, the main focus of the review is to discuss the enormous amount of exciting research on fluorinated liquid crystals that has been reported. The small size of the fluoro substituent enables its incorporation into all types of liquid crystal, including calamitic, discotic, banana, lyotropic, and polymers, without ruining the liquid crystalline nature of the material. However the fluoro substituent is larger than hydrogen, and hence causes a significant steric effect, which combined with the high polarity, confers many fascinating, and often remarkable, modifications to melting point, mesophase morphology and transition temperatures, and the many other very important physical properties, such as dielectric anisotropy, optical anisotropy, and visco-elastic properties. There are many different positions within a liquid crystal structure where a fluoro substituent can be located, including (i) a terminal position, (ii) within a terminal chain, as a semi-fluorinated or as a perfluorinated chain, or as one fluoro substituent at a chiral centre, (iii) as part of a linking group, and (iv) a lateral position in the core section. Such variety enables the interesting and advantageous tailoring of properties, both for the fundamental purposes of establishing structure–property relationships, and for materials targeted towards commercially-successful liquid crystal display applications.

Progress in Physical Organic Chemistry

Abstract: The Nature and Analysis of Substituent Electronic Effects Substituent Effects on Ground-State Molecular Structures and Charge Distributions Some Theoretical Studies of Electronic Substituent Effects in Organic Chemistry Electronic Substituent Effects in Molecular Spectroscopy Superbasic Ion Pairs: Alkali Metal Salts of Alkylarenes A General Treatment of Electrical Effects.

Synthesis and Performance of Polymerizable Room-Temperature Ionic Liquids as Gas Separation Membranes

Abstract: Room-temperature ionic liquids (RTILs) with polymerizable groups can be readily converted into solid, dense poly(RTILs) for use as gas separation membranes. A series of RTIL monomers with varying length n-alkyl substituents were synthesized and converted into polymer films. These membranes were tested for their performance in separations involving CO2, N2, and CH4. CO2 permeability was observed to increase in a nonlinear fashion as the n-alkyl substituent was lengthened. CO2/N2 separation performance was relatively unaffected as CO2 permeability increased. Plotting the performance of these membranes on a “Robeson plot” for CO2/N2 shows that first-generation poly(RTILs) “hug” the “upper bound” of the chart, indicating that they perform as well or better than many other polymers for this separation. The CO2/CH4 separation is less impressive when compared to other polymer membranes on a “Robeson plot”, but poly(RTILs) perform as well or better than molten RTILs do in bulk fluid gas absorptions for that gas p...

Aryl-substituted C3-bridged oligopyrroles as anion receptors for formation of supramolecular organogels.

Abstract: BF2 complexes of aryl-substituted dipyrrolyldiketones (3a-c, 5a-d) have been synthesized by the condensation of arylpyrroles obtained by Suzuki cross-coupling reactions with malonyl chloride, followed by treatment with BF3.OEt2. The binding constants (Ka11) of the BF2 complexes (3a-c) for various anions (Cl-, Br-, CH3CO2-, H2PO4-, and HSO4-) in CH2Cl2 decrease in the order Ph (3a) > o-tolyl (3b) > 2,6-Me2Ph (3c), possibly because of differences in the planarity and the number of interacting o-CH units at the binding sites. Aryl-substituted receptors exhibit a [1+1] binding mode with Cl- as well as a [2+1] binding mode under conditions of high concentration and low temperature, as suggested by 1H NMR studies in CD2Cl2. These receptors, especially phenyl-substituted (3a) and o-tolyl (3b), exhibit drastic colorimetric and fluorescent changes in the presence of F- due to extended pi-conjugation, as compared to 2,6-dimethylphenyl (3c) and the previously reported derivatives (1a-c). Aryl-substitution at the alpha-positions of pyrrole is an excellent means for the introduction of various substituents at the periphery of the anion receptors. For example, derivatives with long alkoxy chains at 3,4,5-positions of the substituent aryl rings (5b-d) afford emissive gel structures in hydrocarbon solvents, such as octane, based on the stacking of slipped H- and J-aggregates at the core pi-plane. The structural organization of the supramolecular gels was investigated by AFM, SEM, and XRD measurements as well as by considering the solid-state packing of crystalline derivatives. The slow transformation of the gel to the solution phase by the addition of various anions, possibly except for F-, is correlated with the unique properties of these acyclic receptors where inversions of pyrrole rings are required for anion binding. Boron complexes of 1,3-dipyrrolyl-1,3-propanediones with aryl-substituents, as a new class of acyclic anion receptors, have shown efficient binding due to the interacting o-CH units and, in the case of the derivative with long aliphatic chains, afforded the emissive supramolecular organogels using stacking of core pi-planes controlled by external chemical stimuli.

Design and Synthesis of Chiral α,α-Disubstituted Amino Acids and Conformational Study of Their Oligopeptides

Abstract: alpha,alpha-Disubstituted amino acids are alpha-amino acids in which the hydrogen atom at the alpha-position of the L-alpha-amino acid is replaced with an alkyl substituent. The introduction of an alpha-alkyl substituent changes the properties of amino acids, with the conformational freedom of the side chain in the amino acids and the secondary structure of their peptides being especially restricted. The author developed a synthetic route of optically active alpha-ethylated alpha,alpha-disubstituted amino acids using chiral cyclic 1,2-diol as a chiral auxiliary. It was found that the preferred secondary structure of peptides composed of chiral alpha-ethylated alpha,alpha-disubstituted amino acids is a fully extended C5-conformation, whereas that of peptides composed of chiral alpha-methylated alpha,alpha-disubstituted amino acids is a 3(10)-helical structure. Also, a new chiral cyclic amino acid; (3S,4S)-1-amino-3,4-di(methoxy)cyclopentanecarboxylic acid {(S,S)-Ac5c(dOM)}, and a bicyclic amino acid; (1R,6R)-8-aminobicyclo[4.3.0]non-3-ene-8-carboxylic acid {(R,R)-Ab5,6= c}, in which the alpha-carbon atom is not the chiral center but chiral centers exist at the side-chain cycloalkane skeleton, were designed and synthesized. The (S,S)-Ac5c(dOM) hexa- and octapeptides preferentially formed left-handed (M) helices, in which the helical-screw direction is exclusively controlled by the side-chain chiral centers. Contrary to the left-handed helices of (S,S)-Ac(5)c(dOM) peptides, the (R,R)-Ab5,6= c hexapeptide formed both diastereomeric right-handed (P) and left-handed (M) helices, and the twelve chiral centers at the side chain showed no preference for helical-screw direction. Thus, the chiral environment at the side chain is important for the control of helical-screw direction. Furthermore, the author designed a new class of chiral cyclic alpha,alpha-disubstituted amino acids that have pendant chiral centers at the substituent of the delta-nitrogen atom. The synthetic route would provide various optically-active cyclic alpha,alpha-disubstituted amino acids bearing a pendant chiral moiety.

Intramolecular “Hydroiminiumation” of Alkenes: Application to the Synthesis of Conjugate Acids of Cyclic Alkyl Amino Carbenes (CAACs)

Abstract: Nitrogen-containing heterocyclic systems have attracted considerable interest over the years because they form the core structures, and are key intermediates, of natural products.[1] One of the most appealing synthetic approaches for their preparation is the intramolecular hydroamination of alkenes, in which the nitrogen–carbon bond is formed by addition of an amine to an olefin.[2] Various catalysts have been used to effect this transformation, which include alkali metals,[3] early[4] and late transition metals,[5] and f-block elements.[6] Interestingly, despite the buffering effect of amines, intramolecular[7] and even intermolecular[8] acid-catalyzed hydroaminations have recently been developed. Schlummer and Hartwig[7a] reported the cyclization of amino alkenes bearing an electron-withdrawing group on the nitrogen atom by catalysis with triflic or sulfuric acid (20 mol %; Scheme 1). A mechanistic study of this process suggested that in contrast to similar transformations using various electrophiles as promoters (for example, iodine-,[9] bromine-,[10] and selenium-based electrophiles[11]), the first step was protonation of the amine, followed by intramolecular transfer of the proton to the double bond in the rate-determining step, and lastly trapping of the generated cation by the amino group. Accordingly, in the absence of electron-withdrawing groups on the nitrogen atom, the cyclization does not occur because of the excessive basicity of the amino group, which prevents the transfer of the proton to the olefin. Scheme 1 a) Schematic representation of acid-catalyzed intramolecular hydroamination; EWC = electron-withdrawing group, n = l,2. b) The hydroiminiumation reaction as a potential synthetic route to cyclic iminium salts A. c) CAAC/H+ salts A′, the precursors ... Imines are certainly less basic than amines, and therefore it was decided to investigate the feasibility of “hydroiminiumation” reactions, which would be an atom-economical route to cyclic iminum salts A (Scheme 1). Providing there is a bulky aryl substituent on the nitrogen atom and that there is a quaternary carbon atom in the position α to the aldiminium carbon atom, salts A′ are the direct precursors of stable cyclic alkyl amino carbenes (CAACs) B.[12] We have shown that CAACs can compete with N-heterocyclic carbenes (NHCs)[13] as ligands for transition-metal-based catalysts,[12a] and also allow the preparation of very low coordinate transition-metal centers.[12b] We report herein our preliminary results on the scope of the thermally induced hydroiminiumation reaction and its application to the synthesis of a variety of CAAC precursors. To establish the viability of this hydroiminiumation methodology, the synthesis of the previously reported CAAC/H+ compound 4a[12a] was chosen as an initial test. Deprotonation of aldimine 1a, derived from 2,6-diisopropyl-aniline (DippNH2) and cyclohexane carboxaldehyde, with lithium diisopropylamide (LDA) leads to the corresponding 1-aza-allyl anion, which readily reacts at room temperature with 3-bromo-2-methylpropene (or 3-chloro-2-methylpropene) to afford the alkenyl aldimine 2a in 94% yield (Scheme 2). Addition of a stoichiometric amount of a 2M solution of HCl/Et2O to a toluene solution of 2a at −78 °C resulted in the immediate formation of a white precipitate. After 15 minutes at −78 °C, the mixture was allowed to warm to room temperature and stirring was continued for an additional 15 minutes. After filtration and recrystallization from chloroform, a new compound 3a was isolated as white crystals in 92% yield. The ionic character of 3a was apparent from its low solubility in toluene, while its acyclic nature was revealed by the presence of a 13C NMR signal at δ = 117.0 ppm from an ethylenic CH2 fragment. The protonation of the nitrogen atom was indicated by a 1H NMR signal at δ = 15.5 ppm, and by the deshielding of the N=CH 13C and 1H NMR signals (2a: (δ = 173.6 and 7.6 ppm; 3a: (δ = 189.8 and 8.0 ppm). A single-crystal X-ray diffraction study unambiguously proved the alkenyl aldiminium structure of 3a (Figure 1). [14] Pleasingly, it was noted that heating an aceto-nitrile solution of 3a in a tube sealed by a teflon stopcock at 50 °C for 18 h afforded the desired cyclic iminium salt 4a in 88% yield. Obviously, the last two steps of the synthesis (2a→4a) can be performed in situ, and the best results (88% yield of isolated product) were obtained when a twofold excess of HCl was used. The overall transformation (1a→4a) can thus be done in 83% yield, which compares extremely favorably with the previously reported method (48 % yield); moreover, the new route uses the same precursor 1a, but avoids the use of the costly reagents 1,2-epoxy-2-methylpropane and trifluoromethane sulfonic anhydride. Figure 1 Molecular structure of 3a in the solid state. Scheme 2 Influence of the nature of the R and R1 substituents on the rate of the hydroiminiumation reaction; Dipp = 2,6-iPr2C6H3; Mes = 2,4,6-Me3C6H2. [a] Time and temperature required for complete conversion of 3. [b] Yield of isolated product, without isolation ... To study the influence of various steric and electronic factors on the hydroiminiumation reaction, several different alkenyl aldimines 2b–h were prepared (Schemes 2, ​,3,3, and ​and4).4). Without exception, the protonation occurred smoothly at the nitrogen atom, and the ensuing alkenyl aldiminium salts 3b–h were obtained in good to excellent yields. The cyclization process occurs slightly more easily when bulky substituents are used on both sides of the NCC fragment (Scheme 2). Indeed, when two methyl groups were used in place of the cyclohexyl group of 3a, the formation of 4b required 24 h at 50 °C, whereas for derivative 3c (Ar = Mes, CR1R1 = CMe2) 24 h at 70 °C are necessary to achieve complete conversion. Not surprisingly, a limitation to the methodology was found when an electron-donating tert-butyl group was placed on the nitrogen atom. Here, because of the high basicity of the nitrogen center, no trace of the cyclic iminium salt 4d was detected when a toluene solution of 3d was heated at 110°C for 24 h. Scheme 3 Influence of the nature of the alkene substituents R1 and R2 on the rate and regioselectivity of the hydroiminiumation reaction. Tos=toluene-4-sulfonyl. [a] Time and temperature required for complete conversion of 3. [b] Yield of isolated product, without ... Scheme 4 Synthesis of six-membered heterocyclic aldiminium salt 4h. Use of alkenyl aldiminium salts 3a and 3e–g allowed study of the influence of the substitution pattern of the carbon–carbon double bond on the fate of the hydroiminiumation reaction, especially with regard to its regioselectivity (Scheme 3). The temperature required for cyclization was found to increase along the series 3a<3e<3f<3g. More importantly, in all cases five-membered heterocycles 4 resulting from exo cyclization were obtained, with no trace of the six-membered-ring isomers being detected. Strikingly, the cyclization of 3g affords exclusively five-membered heterocycle 4g (Figure 2), despite the presence of a phenyl group at the terminal carbon atom of the olefin, which would be expected to stabilize a benzylic carbocation intermediate. Together these observations favor a mechanism in which the proton would be transferred intramolecularly to the double bond in the rate-determining step, similarly to the mechanism proposed by Schlummer and Hartwig for the acid-catalyzed hydroamination reaction.[7a] When compared to the latter reaction involving alkenyl amine I, for which the formation of the six-membered ring II was observed, our result suggests that the addition of N—H across the double bond has a greater “concerted” character[15] in the hydroiminiumation than in the hydroamination reaction.[7a] Figure 2 Molecular structures of 3g (left) and 4g (right) in the solid state. Six-membered heterocyclic aldiminium salts can also be accessed as shown by the preparation of 4h (Scheme 4). However, as observed in the hydroamination reaction,[7a] the cyclization to 4h is more difficult than for the homologous five-membered ring 4e. Besides the easy preparation of a wide variety of CAAC/H+ compounds, the intramolecular hydroiminiumation reported here features some distinct advantages when compared to the intramolecular hydroamination reaction. The resulting iminium ions are very reactive, potentially allowing for the subsequent addition of a large range of nucleophiles, and since they are often prochiral, this chemistry offers the possibility of facile construction of a new stereogenic center a to the nitrogen atom. The extension of this work to other protonated sp2-nitrogen-containing species is under active investigation.

Selective bromination of perylene diimides under mild conditions.

Abstract: A novel method for the bromination of perylene diimides, PDI (1), under mild conditions is reported. Variation of the reaction conditions allows mono- and dibromination of PDIs to afford 2 and 3 (these can be separated through standard procedures) or exclusive dibromination to afford 3. Pure 1,7 regioisomers are obtained through repetitive crystallization. The structure of 1,7-3b was elucidated by a single-crystal X-ray analysis. The facility of the bromination reaction, which decreases in the order 1a > 1b > 1c, depends on PDI aggregation propensities. Monobrominated PDIs were utilized for the syntheses of novel unsymmetrical piperidinyl (4a and 4b) and trimethylsilylethynyl derivatives (5a and 5b). Computational studies (DFT) on imide substituent rotation in PDIs reveal that in the case of bulky groups there is a restricted rotation leading to isomers, in agreement with our experimental results. An aromatic core twist in PDIs bearing one and two bromine substituents was also investigated by DFT.

Transition metal complex and light-emitting device

Abstract: A light-emitting device comprising a pair of electrodes and one or more organic layers disposed between the electrodes, the one or more organic layers comprising a light-emitting layer. At least one of the organic layers comprises a transition metal complex containing a moiety represented by the following formula (1): wherein M 11 represents a transition metal ion; and R 11 , R 12 , R 13 , R 14 , R 5 , R 16 and R 17 represent a substituent or a single bond, respectively, or a tautomer thereof.

Insights into the strength and origin of halogen bonding: the halobenzene-formaldehyde dimer.

Abstract: The observation of short halogen-carbonyl oxygen interactions in protein-ligand complexes has spurred us to use computational tools to better understand the strength of halogen bonding interactions. In this study we have produced potential energy curves for the halogen bonding interactions of several halobenzene-formaldehyde complexes. It was found that, for most halogen substituents, a halobenzene and formaldehyde form stable halogen bonded complexes with interaction energies that increase as the size of the halogen substituent increases.

Meta Conjugation Effect on the Torsional Motion of Aminostilbenes in the Photoinduced Intramolecular Charge-Transfer State

Abstract: The photochemical behavior of a series of trans-3-(N-arylamino)stilbenes (m1, aryl = 4-substituted phenyl with a substituent of cyano (CN), hydrogen (H), methyl (Me), or methoxy (OM)) in both nonpolar and polar solvents is reported and compared to that of the corresponding para isomers (p1CN, p1H, p1Me, and p1OM). The distinct propensity of torsional motion toward a low-lying twisted intramolecular charge-transfer (TICT) state from the planar ICT (PICT) precursor between the meta and para isomers of 1CN and 1Me reveals the intriguing meta conjugation effect and the importance of the reaction kinetics. Whereas the poor charge-redistribution (delocalization) ability through the meta-phenylene bridge accounts for the unfavorable TICT-forming process for m1CN, it is such a property that slows down the decay processes of fluorescence and photoisomerization for m1Me, facilitating the competition of the single-bond torsional reaction. In contrast, the quinoidal character for p1Me in the PICT state kinetically fa...

Ligand effects on dioxygen activation by copper and nickel complexes: reactivity and intermediates.

Abstract: Copper and nickel complexes having various active-oxygen species Mn–O2 (n = 1 or 2), such as trans-(μ-1,2-peroxo)CuII2, bis(μ-oxo)MIII2, bis(μ-superoxo)NiII2, and ligand-based alkylperoxo-MIIn, can be produced by a series of tetradentate tripodal ligands (TMPA analogues) containing sterically demanding 6-methyl substituent(s) on the pyridyl group(s), where TMPA = tris(2-pyridylmethyl)amine. Roles of the methyl substituent(s) for the formation of the active-oxygen species and their oxidation reactivities are reported.

Role of Cation−π Interactions in the Photodimerization of trans-4-Styrylpyridines

Abstract: In order to explore the contribution of the cation−π interaction in the photocyclodimerization of styrylpyridines, the effects of the acid concentration and the substituent on the aryl ring on the product distribution were investigated. The structures of the product dimers were clarified by X-ray crystallographic analysis. In addition, the X-ray packing structures of trans-4-styrylpyridine (1) and its HCl salt were compared. On increasing the acid amount, the yield of the syn-HT dimer significantly increased, whereas that of the cis-isomer decreased. The substituent on the aromatic ring had a significant effect on the product distribution. Irradiation of the substrate styrylpyridine bearing a CF3 group resulted in much lower selectivity, whereas the photolysis of the substrate having a MeO group resulted in a syn-HT dimer in 95% selectivity. Comparison of the X-ray packing structures of 1a and 1a·HCl clarified the significant differences between them. The molecules of 1a·HCl are packed alternately in anti...

Identification of the products of oxidation of quercetin by air oxygen at ambient temperature.

Abstract: Oxidation of quercetin by air oxygen takes place in water and aqueous ethanol solutions under mild conditions, namely in moderately-basic media (pH approximately 8-10) at ambient temperature and in the absence of any radical initiators, without enzymatic catalysis or irradiation of the reaction media by light. The principal reaction products are typical of other oxidative degradation processes of quercetin, namely 3,4-dihydroxy-benzoic (proto-catechuic) and 2,4,6-trihydroxybenzoic (phloroglucinic) acids, as well as the decarboxylation product of the latter--1,3,5-trihydroxybenzene (phloroglucinol). In accordance with the literature data, this process involves the cleavage of the gamma-pyrone fragment (ring C) of the quercetin molecule by oxygen, with primary formation of 4,6-dihydroxy-2-(3,4-dihydroxybenzoyloxy)benzoic acid (depside). However under such mild conditions the accepted mechanism of this reaction (oxidative decarbonylation with formation of carbon monoxide, CO) should be reconsidered as preferably an oxidative decarboxylation with formation of carbon dioxide, CO2. Direct head-space analysis of the gaseous components formed during quercetin oxidation in aqueous solution at ambient temperature indicates that the ratio of carbon dioxide/carbon monoxide in the gas phase after acidification of the reaction media is ca. 96:4%. Oxidation under these mild conditions is typical for other flavonols having OH groups at C3 (e.g., kaempferol), but it is completely suppressed if this hydroxyl group is substituted by a glycoside fragment (as in rutin), or a methyl substituent. An alternative oxidation mechanism involving the direct cleavage of the C2-C3 bond in the diketo-tautomer of quercetin is proposed.

Synthesis, spectral properties and photostability of novel boron-dipyrromethene dyes

Abstract: Two series of novel boron–dipyrromethene (BODIPY) dyes containing 8-phenyl groups have been synthesized and their spectral properties have been studied. Series 2 with four methyl groups at 1,3,5,7-positions show much higher fluorescence quantum yields and extinction coefficients than series 1 (without methyl groups). The “push–pull” electronic effect caused by the methyl groups at 3 and 5 positions is a significant positive factor to the high quantum yields of 2 . The X-ray structure analysis of 1c and 2c reveals that steric expulsion exists between the phenyl and adjacent two methyl groups. Moreover, the steric expulsion might block the intramolecular vibronic relaxation and internal conversion of the excited 2 , which also contributes to their high fluorescence quantum yields. The substituent effects on photostability and redox potentials of these dyes have been discussed.

Treatment of duchenne muscular dystrophy

Abstract: There are disclosed compound of Formula (1): A1, A2, A3 and A4 which may be the same or different, represent N or CR1, X is a divalent group selected from O, S(O)n, C=W, NR4, NC(=O)R5 and CR6R7, W is O, S, NR20, Y is N or CR8, one of R4, R5, R6, R8, R9 and NR20 represents - L -R3, in which L is a single bond or a linker group, additionally, R1, R3 - R9, which may be the same or different, independently represent hydrogen or a substituent and R20 represents hydrogen, hydroxyl, alkyl optionally substituted by aryl, alkoxy optionally substituted by aryl, aryl, CN, optionally substituted alkoxy, optionally substituted aryloxy, optionally substitute alkanoyl, optionally substituted aroyl, NO2, NR30R31, in which R30 and R31, which may be the same or different, represent hydrogen, optionally substituted alkyl or optionally substituted aryl; additionally, one of R30 and R31 may represent optionally substituted alkanoyl or optionally substituted aroyl, n represents an integer from 0 to 2, in addition, when an adjacent pair of A1 - A4 each represent CR1, then the adjacent carbon atoms, together with their substituents may form a ring B, when X is CR6R7, R6 and R7, together with the carbon atom to which they are attached may form a ring C, or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for the therapeutic and/or prophylactic treatment of Duchenne muscular dystrophy, Becker muscular dystrophy or cachexia.

Inorganic–organic hybrid materials incorporating primary cyclic ammonium cations: The lead iodide series

Abstract: Six inorganic–organic hybrids have been synthesized and characterised by single-crystal X-ray diffraction experiments. The inorganic component is based on lead(II) iodide units and the organic component various cyclic hydrocarbons with only a primary ammonium group as a ring substituent. If the organic component is cyclopropylammonium, cyclobutylammonium, cyclopentylammonium and cyclohexylammonium, the inorganic motif observed is based on the cubic perovskite structure type and consists of 2-D layers of corner-sharing octahedra, in the ratio of 1∶2 inorganic–organic. lead(II) iodide and cycloheptylammonium combined to give 1-D chains of corner-sharing lead iodide octahedra and similarly, lead(II) iodide and cyclooctylammonium gave 1-D chains of face-sharing octahedra. A quantitative measure of the steric effects of the size of the cyclic rings on the tilting of the inorganic layers is proposed.

Syntheses and properties of core-substituted naphthalene bisimides with aryl ethynyl or cyano groups

Abstract: This paper reports the synthesis, the absorption and the emission spectra and the electrochemical and spectroelectrochemical properties of new naphthalene bisimides substituted in positions 2 and 6 of the napthyl core by cyano, pyrrolidino, 4-phenylethynyl, 4-ethynyl-N,N-dihexylaniline or 4-cyanophenyl groups. The synthesis of these five new compounds shares the common precursor: 2,6-dibromonaphthalene tetracarboxylic dianhydride. We show that the aryl ethynyl substituent red-shifts the absorbance and enhances the fluorescence quantum yield of the naphthalene bisimide, making these new compounds potential useful dyes. The cyano groups directly connected to the naphthyl core significantly decrease the two first reduction potentials of the molecule. The large electron affinity and the stability of the radical anion of the latter compound make it ideally suited to transport electrons or to act as an electron acceptor.

Iron(II) complexes ligated by 2-imino-1,10-phenanthrolines: Preparation and catalytic behavior toward ethylene oligomerization

Abstract: A series of N,N,N-tridentate iron (II) complexes bearing 2-imino-1,10-phenanthrolines, [2-{(2,6-R 1 ,R 3 -4-R 2 -C6H2)N C(R)}-1,10-phen]FeCl2, was synthesized and characterized by IR spectroscopy and elemental analysis. One of these complexes (18b) was determined by single-crystal X-ray crystallography for its unambiguous structure. These iron(II) complexes were found to exhibit remarkable activities for ethylene oligomerizatio ni n the presence of MAO or MMAO cocatalyst affording -olefins with high selectivity and the composition of oligomers followed the Schluz–Flory distribution. The effects of substituents on imino fragment on the activity were explored in detail; complexes with mono substituent at the orthoposition of the phenyl ring showed high activities with low K values, suggesting that fine tuning of the steric bulk of substituents on the imino fragment directly affects both the activity and the selectivity. © 2007 Elsevier B.V. All rights reserved.

Aging of a donor conjugated polymer: Photochemical studies of the degradation of poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene]

Abstract: This article is devoted to the study of the photoaging and thermal aging of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV; also called OC1C10-PPV) used in organic solar cells. Thin MDMO-PPV films (thickness 300 nm) in the presence of air or thermooxidized at 60°C. The modifications of the chemical structure of the matrix were analyzed with ultraviolet-visible and infrared spectroscopy. The oxidation products that formed were identified by postirradiation treatments, including chemical derivatization reactions. On the basis of the identification of the various products formed, a two-step radical mechanism is proposed to account for the modification of the chemical structure of the polymeric matrix. It involves first the oxidation of the ether substituent followed by the oxidation of the double bonds. These reactions are responsible for a loss of conjugation of MDMO-PPV, chain scissions, and a decrease in the visible absorbance, which are anticipated to drastically impair the photovoltaic properties of the material.

Compound and its tautomer, metal complex compound, colored photosensitive curing composition, color filter, and method for producing the same

Abstract: PROBLEM TO BE SOLVED: To provide a colored photosensitive curing composition useful for color filters in primary colors, including blue, green and red, having a high molar absorption coefficient and allowing a reduction in film thickness and superior color purity and robustness. SOLUTION: The colored photosensitive curing composition comprises, as its colorant, a dipyrromethene-based metal complex compound obtained from a metal or metal compound and a dipyrromethene-based compound represented by general formula (I), wherein R 1 -R 6 each independently represent a hydrogen atom or a substituent group; and R 7 represents a hydrogen or halogen atom, or an alkyl, aryl or heterocyclic group. COPYRIGHT: (C)2009,JPO&INPIT

Systematic studies of early actinide complexes: uranium(IV) fluoroketimides.

Abstract: The reaction of (C 5 Me 5 ) 2 U(CH 3 ) 2 with 2 equiv of N≡C-Ar F gives the fluorinated uranium(IV) bis(ketimide) complexes (C5Me5)2U[-N=C(CH3)(Ar F )] 2 [where Ar F = 2-F-C 6 H 4 (4), 3-F-C 6 H 4 (5), 4-F-C 6 H 4 (6), 2,6-F 2 -C 6 H 3 (7), 3,5-F 2 -C 6 H 3 (8), 2,4,6-F 3 -C 6 H 2 (9), 3,4,5.F 3 -C 6 H 2 (10), and C 6 F 5 (11)]. These have been characterized by single-crystal X-ray diffraction, 1 H and 19 F NMR, cyclic voltammetry, UV-visible-near-IR absorption spectroscopy, and variable-temperature magnetic susceptibility. Density functional theory (DFT) results are reported for complexes 6 and 11 for comparison with experimental data. The most significant structural perturbation imparted by the F substitution in these complexes is a rotation of the fluorinated aryl (Ar F ) group out of the plane defined by the N=C(C Me )(C ipso ) fragment in complexes 7, 9, and 11 when the Ar F group possesses two o-fluorine atoms. Excellent agreement is obtained between the DFT-calculated and experimental crystal structures for 11, which displays the distortion, as well as for 6, which does not. In 7, 9, and 11, the out-of-plane rotation results in large angles (Φ = 53.7-89.4°) between the planes formed by ketimide atoms N=C(C Me )(C ipso ) and the ketimide aryl groups. Complexes 6 and 10 do not contain o-fluorine atoms and display interplanar angles in the range of Φ = 7-26.8°. Complex 4 with a single o-fluorine substituent has intermediate values of Φ = 20.4 and 49.5°. The distortions in 7, 9, and 11 result from an unfavorable steric interaction between one of the two o-fluorine atoms and the methyl group [-N=C(CH 3 )] on the ketimide ligand. All complexes exhibit U V /U IV and U IV /U III redox couples, although the distortion in 7, 9, and 11 appears to be a factor in rendering the U IV /U III couple irreversible. The potential separation between these couples remains constant at 2.15 ± 0.03 V. The electronic spectra are dominated by unusually intense f-f transitions in the near-IR that retain nearly identical band energies but vary in intensity as a function of the fluorinated ketimide ligand, and visible and near-UV bands assigned to metal (5f)-to-ligand (π*) charge-transfer and interconfiguration (5f 2 → 5f 1 -6d 1 ) transitions, respectively. Variable-temperature magnetic susceptibility data for these complexes indicate a temperature-independent paramagnetism (TIP) below ∼50 K that results from admixing of low-lying crystal-field excited states derived from the symmetry-split 3 H 4 5f 2 manifold into the ground state. The magnitude of the TIP is smaller for the complexes possessing two o-fluorine atoms (7, 9, and 11), indicating that the energy separation between ground and TIP-admixed excited states is larger as a consequence of the greater basicity of these ligands.

Selective ruthenium-catalyzed transformations of enynes with diazoalkanes into alkenylbicyclo[3.1.0]hexanes.

Abstract: Reaction of a variety of C⋮CH bond-containing 1,6-enynes with N2CHSiMe3 in the presence of RuCl(COD)Cp* as catalyst precursor leads, at room temperature, to the general formation of alkenylbicyclo[3.1.0]hexanes with high Z-stereoselectivity of the alkenyl group and cis arrangement of the alkenyl group and an initial double-bond substituent, for an E-configuration of this double bond. The stereochemistry is established by determining the X-ray structures of three bicyclic products. The same reaction with 1,6-enynes bearing an R substituent on the C1 carbon of the triple bond results in either cyclopropanation of the double bond with bulky R groups (SiMe3, Ph) or formation of alkylidene−alkenyl five-membered heterocycles, resulting from a β elimination process, with less bulky R groups (R = Me, CH2CHCH2). The reaction can be applied to in situ desilylation in methanol and direct formation of vinylbicyclo[3.1.0]hexanes and to the formation of some alkenylbicyclo[4.1.0]heptanes from 1,7-enynes. The catalytic ...

Electrostatic potential minimum of the aromatic ring as a measure of substituent constant.

Abstract: The molecular electrostatic potential minimum (Vmin) observed for the arene pi system of a substituted benzene derivatives is found to correlate linearly with the substituent constant sigma(p) degrees . The use of Vmin as a measure of substituent effect is further confirmed by obtaining a linear correlation between Vmin and a thermodynamic measure of the substituent effect obtained from an isodesmic reaction scheme involving benzene derivatives. Vmin and the recently proposed electrostatic potential value at the nucleus of the para carbon atom (Vc) show a nearly identical trend toward quantification of substituent effects. Both quantities have been compared at three different density functional theory methods, viz. B3LYP/6-311+G(2d,2p), BPW91/6-311G(d,p), and B3LYP/aug-cc-pvtz, as well as the at the MP2/6-31+G(d,p) level of theory, showing remarkable consistency among them.