Boron dipyrromethene dyes: a rational avenue for sensing and light emitting devices

Boron dipyrromethene dyes bearing nitro, amino, isocyanate and isothiocyanate functions were readily prepared under mild conditions. Various combinations allow to produce urea, diurea, thiourea, dithiourea in the 3, 4 and 5-substitution positions of the appended phenyl group. Condensation of the 3,4-substituted diamino derivative with 1,10-phenanthroline-5,6-dione and 6-formyl-2-methylpyridine allow to prepare dipyridophenazine and indole derivatives. The 3,5-dinitro-substituted indacene dye was characterized by an X-ray molecular structure showing a pronounced tilt angle of the dinitrophenyl group relative to the indacene core (approximately 84 degrees) whereas one nitro groups is basically coplanar with the phenyl ring and the second titled by approximately 21 degrees. The optical properties of these dyes reveals on/off switching of the fluorescence from the nitro to the amino compounds and further to the urea likely understood in the framework of an photoinduced electron transfer process.     

Polarography of some 2,1,3-benzothiadiazoles,benzofurazans, 2,1,3-benzoselenadiazoles,and 3,4-disubstituted and fused 1,2,5-thiadiazoles

The redox behavior has been determined in acetonitrile solutions at a mercury and platinum electrode for 2,1,3-benzo(group VI)diazoles, and 3,4-disubstituted and fused 1,2,5-thiadiazoles. The derivatives studied contained alkyl, phenyl, bromo, chloro, cyano, nitro, methylsulfonyl, and trifluoromethylsulfonyl groups. All ring systems and their derivatives are reversibly reduced initially in a one-electron step, to their respective radical anion, but the nitro and bromo derivatives are reduced preferentially at the substituent group. The potential at which the production of the radical anion occurred became more anodic as the electron withdrawing ability of the substituent and the number of substituents increased.     

8-Hydroxyquinoline-substituted boron-dipyrromethene compounds: synthesis, structure, and OFF-ON-OFF type of pH-sensing properties

A series of four novel 8-hydroxyquinoline-substituted boron-dipyrromethene derivatives, namely 4,4-difluoro-8-(5-(8-hydroxyquinoline))-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (1), 4,4-difluoro-8-(5-(8-hydroxyquinoline))-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (2), 4,4-difluoro-8-(5-azastyryl-(8-hydroxyquinoline))-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (3), and 4,4-difluoro-8-(5-azastyryl-(8-hydroxyquinoline))-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (4), have been synthesized and characterized by a series of spectroscopic methods. The molecular structures of 1 and 2 have been determined by single-crystal X-ray diffraction analyses. The two methyl substituents attached at C-1 and C-7 positions of boron-dipyrromethene (Bodipy) in compound 2 was revealed to prevent the free rotation of the 8-hydroxyquinoline (8-HQ) moiety, resulting in an almost vertical 8-HQ-Bodipy configuration of this compound. This is obviously different from those for 1 with the dihedral angle between 8-hydroxyquinoline and Bodipy moieties of 65.44 and 66.79° due to the lack of methyl substituents in the latter compound. The intense fluorescence from the Bodipy subunit of these compounds was revealed to gradually get diminished along with either decreasing or increasing the pH value under acidic and basic conditions, respectively, in particular for 1, 2, and 4 because of the photoinduced intramolecular electron transfer from excited Bodipy moiety to 8-HQ unit and just an opposite process. This renders these compounds the first OFF-ON-OFF type of pH-dependent fluorescent sensors. Nevertheless, both the intrinsic fluorescence of these compounds and their fluorescent quenching properties along with the change in the pH value have been found to depend on the steric configuration as well as the linking group between 8-hydroxyquinoline and Bodipy moieties, revealing the effect of molecular structure on their fluorescence properties.     

Electron density distribution in heterocyclic systems with two vicinal nitrogen atoms. III. Dipole moments of some alkyl,aryl, and nitro pyrazole derivatives

Dipole moments of 13 alkyl and aryl derivatives of pyrazole are determined. It is found that fundamentally it is the pyrazole ring that determines the values of these dipole moments. The phenyl group behaves as a weak electron donor with respect to the pyrazole ring. It is shown that under the action of powerful electron-accepting substituents, such as the nitro group, the electron cloud of the pyrazole ring is polarized toward the electron acceptor.For Part II see [1].     

Electronic effects in dianion radicals of nitro derivatives of 2-phenylbenzimidazole

The EPR spectra of the dianion radicals of 5(6)-nitro-2-(4-aminophenyl)benzimidazole (I), 5(6)-nitro-2-phenylbenzimidazole (II), 5(6)-nitro-2-(4-nitrophenyl)benzimidazole (III), 5(6)-nitro-2-(3-nitrophenyl)benzimidazole (IV), and 2-(4-nitrophenyl) benzimidazole (V), obtained by electrochemical reduction in dimethylformamide (DMF) in a Bu₄NClO₄ -base electrolyte in the presence of Bu₄NOH (VI), were studied. Under the influence of VI, these compounds split out a proton from the imidazole ring and give anions I–V, which are capable of adding an electron reversibly. It was shown that the unpaired electron in I and II is localized in the benzimidazole system and that the splitting of the nitrogen atom of the nitro group does not depend significantly on the substituent in the phenyl ring. The introduction of a nitro group in the phenyl ring (III–V) leads to localization of the unpaired electron on it. The nature of the substituent in the benzimidazole system has a significant effect on the splitting constant for the nitrogen atom of the nitro group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 530–531, April, 1979.We thank T. A. Maslennikova for kindly providing us with the compounds for the investigation.     

Mass spectrometry in structural and stereochemical problems—CCIV. Spectra of hydantoins II. Electron impact induced fragmentation of some substituted hydantoins

The mass spectral decomposition modes of hydantoin and derivatives containing alkyl and phenyl substituents have been investigated using isotopic labeling techniques. The loss of carbon monoxide from the molecular ions of these compounds was shown to preferentially involve the C-4 carbonyl group. Other fragmentation processes characteristic of the hydantoin ring system and the effect on this of alkyl and phenyl substitution are described.     

Conformational studies by dynamic NMR. 86. Structure, stereodynamics, and cryogenic enantioseparation of the stereolabile isomers of o-dinaphthylphenyl derivatives

Static and dynamic stereochemistry of the hydrocarbon comprising a phenyl ring bearing two alpha-naphthyl substituents in the ortho positions, i.e., 1,2-di-(4-methyl-naphth-1-yl)-benzene 1, has been studied by a combination of variable temperature NMR, cryogenic HPLC, and MM calculations. Whereas in solution both syn (meso) and anti (chiral) forms were observed and the corresponding interconversion barrier was determined (Delta G(++) = 19.5 kcal mol(-1)), only the diastereoisomer anti was found to be present in the crystalline state (X-ray diffraction). When the molecule is rendered asymmetric by introduction of a nitro group in the phenyl ring as in 1,2-di-(4-methyl-naphth-1-yl)-4-nitrobenzene 2, the chiral syn and anti diastereoisomers are simultaneously present both in solution and in the solid state, albeit in different proportions. Cryogenic chromatography on a HPLC chiral stationary phase at 20 degrees C allowed the stereolabile diastereoisomers and the corresponding enantiomers to be separated.     

l, 9-Substituted fluorenes

The synthesis of 2-methyl (phenyl)-2, 3H-pyridazino-[4, 5, 6-m- l] fluorene-3-methylthionium methylsulfates and of derivatives with substituents in the fluorene ring, is described. Reaction of the latter with heterocyclic hydrazones, and also with compounds containing an active methylene or methyl group, gives cyanine dyes. The electronic spectra of the dyes are measured.For Part III see [3].     

New difluoro-boradiazaindacene shaped with gallate platforms

The present account describes the synthesis of difluoro-boradiazaindacenes (F-Bodipy) functionalized at the central 8-position by phenylamino or phenyldiamino moieties conveniently transformable into phenyl amide scaffoldings. Molecules carrying three linear or branched chains, or six linear chains were prepared and fully characterized. Four X-ray crystal structures were determined and the packing is discussed in terms of molecular interactions, a key feature for the formation of aggregates or thin films. With the exception of nitro derivatives quenched by a photo-induced reductive electron transfer and the amino-derivatives partially quenched, all dyes are highly fluorescent with quantum yields lying between 50 and 90%. The few nanosecond excited-state lifetimes and the weak Stokes shifts are in keeping with singlet excited states. Reversible reduction and oxidation processes occur around −1.34 and +0.97 V in solution and the electroactivity and photoluminescence are maintained in thin films. Interestingly, two distinct emissions are observed at 550 and 635 nm by electroluminescence of the trimethoxyphenyl-Bodipy derivative, corresponding, respectively, to the luminescence of isolated molecules and aggregates. Dispersion of the Bodipy into a fluorescent poly(N-vinylcarbazole) polymer (PVK) (approximately 3 mol% per repeating unit of PVK) by solution processing exclusively produces yellow emission due to isolated Bodipy fluorophore.     

A New Approach to the Synthesis of 2-Nitrobenzaldehyde. Reactivity and Molecular Structure Studies

 New approaches to the synthesis of 2-nitrobenzaldehyde by formation and selective isomer separation of 2-nitrophenyl-1,3-dioxolane and further hydrolysis are reported. In this route, the same acidic heterogeneous catalyst is used for 1,3-dioxolane formation and hydrolysis; it can be recycled several times without loss of efficiency. The ortho/meta isomers of 2-nitrophenyl-1,3-dioxolane can be separated by a combination of stereoselective crystallization and fractionated distillation. This new route reduces safety and environmental hazards in the synthesis of 2-nitro- and 3-nitro-benzaldehydes. The molecular structures of the nitro derivatives were confirmed by ¹H and ¹³C NMR spectroscopy. The results are in accordance with a non-coplanar conformer of the 2-nitro derivatives (2-nitrobenzaldehyde and 2-(2′-nitrophenyl)-1,3-dioxolane), where the nitro group is twisted with respect to the phenyl ring. In contrary, both the carbonyl and the nitro group are coplanar with the phenyl ring in 3-nitrobenzaldehyde. This result is consistent with the reactivity of the compounds.     

A New Approach to the Synthesis of 2-Nitrobenzaldehyde. Reactivity and Molecular Structure Studies

Summary.  New approaches to the synthesis of 2-nitrobenzaldehyde by formation and selective isomer separation of 2-nitrophenyl-1,3-dioxolane and further hydrolysis are reported. In this route, the same acidic heterogeneous catalyst is used for 1,3-dioxolane formation and hydrolysis; it can be recycled several times without loss of efficiency. The ortho/meta isomers of 2-nitrophenyl-1,3-dioxolane can be separated by a combination of stereoselective crystallization and fractionated distillation. This new route reduces safety and environmental hazards in the synthesis of 2-nitro- and 3-nitro-benzaldehydes. The molecular structures of the nitro derivatives were confirmed by ¹H and ¹³C NMR spectroscopy. The results are in accordance with a non-coplanar conformer of the 2-nitro derivatives (2-nitrobenzaldehyde and 2-(2′-nitrophenyl)-1,3-dioxolane), where the nitro group is twisted with respect to the phenyl ring. In contrary, both the carbonyl and the nitro group are coplanar with the phenyl ring in 3-nitrobenzaldehyde. This result is consistent with the reactivity of the compounds. Received January 22, 2001. Accepted (revised) July 18, 2001     

Diazo liquid crystals for potential infrared applications

Nine series of liquid crystals containing an electron-donating group at one end of a conjugated system and an electron-withdrawing group at the other end have been synthesized. The electron-donating group is 4-n-alkylpiperazine and the electron-withdrawing group is the nitro group; and the conjugated system is diphenyldiazene with zero, one or two substituents on the phenyl ring not containing the nitro group. The substituents are-F,-Cl, and-CH₃. Most of the compounds synthesized are nematogenic and exhibit rather broad liquid crystalline ranges. The effects of the lateral substituents on the optical absorption and phase transition temperatures are correlated with their nature and position of substitution. Dielectric anisotropy and birefringence measurements were made using mixtures containing 10 wt % of synthesized liquid crystals dissolved in commercial mixture E7.     

Nitration of some 2, 5-disubstituted 4-phenylpyridin es

2,5-Dimethyl-4-phenylpyridine is nitrated in the para position of the phenyl ring. Further nitration of the resulting nitro compound gives a mixture of isomeric dinitro derivatives. In the case of 4-phenylisocinchomeronic acid the nitro group enters the meta position of the phenyl ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii. No. 3, pp. 365–368, March, 1976.     

Diazo liquid crystals for potential infrared applications

Nine series of liquid crystals containing an electron-donating group at one end of a conjugated system and an electron-withdrawing group at the other end have been synthesized. The electron-donating group is 4-n-alkylpiperazine and the electron-withdrawing group is the nitro group; and the conjugated system is diphenyldiazene with zero, one or two substituents on the phenyl ring not containing the nitro group. The substituents are-F,-Cl, and-CH₃. Most of the compounds synthesized are nematogenic and exhibit rather broad liquid crystalline ranges. The effects of the lateral substituents on the optical absorption and phase transition temperatures are correlated with their nature and position of substitution. Dielectric anisotropy and birefringence measurements were made using mixtures containing 10 wt % of synthesized liquid crystals dissolved in commercial mixture E7.     

Electronic structure of phenyl-N,N-dimorpholinomethanes

The electronic structure of dimorpholinomethane and 11 phenyl derivatives was studied by He 1 photoelectron spectroscopy and AM1 quantum chemical calculations. The π-system of the phenyl ring reacts weakly with the molecular orbitals of dimorpholinomethane. Mutual electronic effects of the dimorpholine and phenyl fragments are estimated. It is shown that for most title compounds, HOMO is localized on the nitrogen atoms of dimorpholinomethane and is independent of the type of substituent in the phenyl ring. An exception is dimethylaminopheny I-N,N-dimorpholinomethane, whose first ionization potential (7.31_eV) is much lower than that for other compounds (8.15-8.53_eV) due to electron withdrawal from the 3π(b₁) MO of the phenyl ring. The relationship between the first ionization potentials and the effective corrosion inhibiting property of the compounds is discussed. Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 4, pp. 753-764, July-August, 2000     

Electronic structure of phenyl-N,N-dimorpholinomethanes

The electronic structure of dimorpholinomethane and 11 phenyl derivatives was studied by He 1 photoelectron spectroscopy and AM1 quantum chemical calculations. The π-system of the phenyl ring reacts weakly with the molecular orbitals of dimorpholinomethane. Mutual electronic effects of the dimorpholine and phenyl fragments are estimated. It is shown that for most title compounds, HOMO is localized on the nitrogen atoms of dimorpholinomethane and is independent of the type of substituent in the phenyl ring. An exception is dimethylaminopheny I-N,N-dimorpholinomethane, whose first ionization potential (7.31_eV) is much lower than that for other compounds (8.15-8.53_eV) due to electron withdrawal from the 3π(b₁) MO of the phenyl ring. The relationship between the first ionization potentials and the effective corrosion inhibiting property of the compounds is discussed. Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 4, pp. 753-764, July-August, 2000     

Substituent Effects in High-Performance Liquid Chromatography of Diarylacrylonitriles

Abstract

Thirty diarylacrylonitriles, carrying various para substituents in the phenyl ring attached to the position l of the ethylenic bridge and various heterorings (thienyl, furyl, pyrryl, N-methylpyrryl) attached to the position 2, have been investigated on silica gel. An additional substituent is present in the thienyl derivatives. The capacity factors of all the compounds can be grouped in only five or six families, according to the variation in the para-phenyl substitution or in the heteroring moiety, respectively. The strongest effect in the enhancement of the capacity factors is given by a methoxy or nitro group in the para-phenyl position.

Other minor effects as well as the relationship between capacity factors and solvent mixtures polarity are discussed.     

Carbon-13 NMR spectra of DDT,its analogues and related compounds

Carbon-13 NMR spectra of mono- and disubstituted aromatic compounds including DDT, its analogues, homologues, derivatives and certain model compounds have been studied. The Savitsky scheme of carbon chemical shifts in disubstituted benzenes is applicable to these compounds. The data obtained show that in mono- and disubstituted aromatic compounds containing two different substituents in the α- and β-positions of the side chain, the substituted ring carbon atom shifts follow the additivity rule and can be calculated from substituent increments. Mutual effects of substituents in the ring and in the side chains are analysed. The chlorine atoms in α-position to the phenyl ring give rise to an additive α-effect of about 25 ppm, as in perchloroalkanes. The influence of a β-chlorine atom in the side chain on the substituted carbon atom in the ring is, however, only 3 ppm as against the usual value of about 10 ppm for the β-effect in alkyl chains. Moreover, the first β-chlorine substituent has no noticeable influence on the substituted ring carbon chemical shift: the effect of 3 ppm is transferred to the para-carbon atom almost without attenuation. The ring substituted carbon atom signal shifts caused by the γ-effect of chlorine in the side chain are similar to those observed in aliphatic chains. The ortho-chlorine substituents shift the side chain α-carbon atom signal by 3.6-5.2 ppm to high field compared to para-chlorophenyl compounds. This is similar to the chlorine γ-effect in aliphatic chains.     

Molecular and electronic structures of anionic σ-complexes of 9-nitroanthracene and its derivatives studied byab initio HF/6-31G** calculations

The molecular structures of anionic σ-complexes of 9-nitroanthracene and its 10-methoxy and 10-acetonyl derivatives were calculated by theab initio quantum-chemical HF/6-31G^** method. The central ring of the anthracene fragment adopts a boat conformation. The values of the bond lengths and bond orders in the compounds under study indicate that the contribution of theaci-resonance form to the structure of the nitro group is substantially larger than that estimated for 2,4,6-trinitrobenzene derivatives. The substituents have no substantial effect on the geometry of the anion. The negative charge is localized mainly on the oxygen atoms of the nitro group and of the substituents. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2142–2145, November, 1998.     

Synthesis and antimicrobial properties of new 2-((4-ethylphenoxy)methyl)benzoylthioureas

New acylthiourea derivatives, 2-((4-ethylphenoxy)methyl)-N-(phenylcarbamothioyl)benzamides, were tested by qualitative and quantitative methods on various bacterial and fungal strains and proved to be active at low concentrations against Gram-positive and Gram-negative bacteria as well as fungi. These compounds were prepared by the reaction of 2-((4-ethylphenoxy)methyl)benzoyl isothiocyanate with various primary aromatic amines, and were characterised by melting point and solubility. The structures were identified by elemental analysis, ¹H and ¹³C NMR, and IR spectral data. The level of antimicrobial activity of the new 2-((4-ethylphenoxy)methyl)benzoylthiourea derivatives was dependent on the type, number and position of the substituent on the phenyl group attached to thiourea nitrogen. The iodine and nitro substituents favoured the antimicrobial activity against the Gram-negative bacterial strains, while the highest inhibitory effect against Gram-positive and fungal strains was exhibited by compounds with electron-donating substituents such as the methyl and ethyl groups.