Color‐Tunable Solid‐State Fluorescence Emission from Carbazole‐Based BODIPYs

Several carbazole‐based boron dipyrromethene (BODIPY) dyes were synthesized by organometallic approaches. Thiazole, benzothiazole, imidazole, benzimidazole, triazole, and indolone substituents were introduced at the 1‐position of the carbazole moiety, and boron complexation of each dipyrrin generated the corresponding compounds 1 , 2 a , and 3 – 6 . The properties of these products were investigated by UV/Vis and fluorescence spectroscopy, cyclic voltammetry, X‐ray crystallography, and DFT calculations. These compounds exhibited large Stokes shifts, and compounds 1 , 2 a , and 3 – 5 fluoresced both in solution and in the solid state. Complex 2 a showed the highest fluorescence quantum yield (Φ_F) in the solid state, therefore boron complexes of the carbazole–benzothiazole hybrids 2 b – f , which had several different substituents, were prepared and the effects of the substituents on the photophysical properties of the compounds were examined. The fluorescence properties showed good correlation with the results of crystal‐packing analyses, and the dyes exhibited color‐tunable solid‐state fluorescence.     

Syntheses and characterization of carbazole based new low‐band gap copolymers containing highly soluble benzimidazole derivatives for solar cell application

Newly designed 2H‐benzimidazole derivatives which have solubility groups at 2‐position have been synthesized and incorporated into two highly soluble carbazole based alternating copolymers, poly[2,7‐(9‐(1′‐octylnonyl)‐9H‐carbazole)‐alt‐5,5‐(4′,7′‐di(thien‐2‐yl)‐2H‐benzimidazole‐2′‐spirocyclohexane)] (PCDTCHBI) and poly[2,7‐(9‐(1′‐octylnonyl)‐9H‐carbazole)‐alt‐5,5‐(4′,7′‐di(thien‐2‐yl)‐2H‐benzimidazole‐2′‐spiro‐4′′‐((2′′′‐ethylhexyl)oxy)‐cyclohexane)] (PCDTEHOCHBI) for photovoltaic application. These alternating copolymers show low‐band gap properties caused by internal charge transfer from an electron‐rich unit to an electron‐deficient moiety. HOMO and LUMO levels are –5.53 and –3.86 eV for PCDTCHBI, and –5.49 and –3.84 eV for PCDTEHOCHBI, respectively. Optical band gaps of PCDTCHBI and PCDTEHOCHBI are 1.67 and 1.65 eV, respectively. The new carbazole based the 2H‐benzimidazole polymers show 0.11–0.13 eV lower values of band gaps as compared to that of carbazole based benzothiadiazole polymer, poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT), while keeping nearly the same deep HOMO levels. The power conversion efficiencies of PCDTCHBI and PCDTEHOCHBI blended with [6,6]phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) are 1.03 and 1.15%, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Chemical properties of <Emphasis Type="Italic">N</Emphasis>-polyfluoroethylimidazole and -pyrrole derivatives

Bromination, acylation, nitration, and metallation of imidazole and pyrrole derivatives containing the difluoromethylene fragment at the N atom were studied. 1-(1,1,2,2-Tetrafluoroethyl)pyrrole, 1-(1,1,2,2-tetrafluoroethyl)imidazole, and 1-(2-chloro-1,1,2-trifluoroethyl)imidazole were used as substrates. 1-Alkyl-3-(1,1,2,2-tetrafluoroethyl)- and 1-alkyl-3-(2-chloro-1,1,2-trifluoroethyl)imidazolium iodides were obtained. These can be used as intermediates for preparation of new ionic liquids of the imidazole series and 1-alkyl-3-polyfluoroethylimidazole-2-thiones.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 781–787, March, 2005.     

Some reactions of fluorosulfonyldifluoroacetic acid with N-heterocyclic compounds

Difluorocarbene generated from the decomposition of fluorosulfonyldifluoroacetic acid (2)reacted with various sodium salts of N-heterocyclic compounds(1) giving the corresponding difluoro-methylated products in acetonitrile at 10—40℃.Benzotriazole(1a),benzimidazole(1b) and imidazole(1c) were converted into 1-(difluoromethyl)benzotriazole(3a),1-(difluoromethyl)benzimidazole(3b) and1-(difluoromethyl)imidazole(3c)respectively.Indole(1d)reacted with 2 to give -(fluorosulfonyldifluoro-acetate)indole(2d) rather than the expected difluoromethylated derivatives.     

Solid–Liquid Phase Alkylation of N-Heterocycles: Microwave-Assisted Synthesis as an Environmentally Friendly Alternative

The solid–liquid phase alkylation of a variety of five-membered N-heterocycles (carbazole, imidazole, benzimidazole, and indole-3-carbaldehyde) was carried out under different conditions. The use of alkali carbonate in dimethylformamide or in MeCN (in the latter case, in the presence of a phase-transfer catalyst) is a suitable method to prepare the corresponding N-alkylated products in an efficient way. In most cases, the solventless, microwave-assisted reaction is an environmentally friendly alternative to traditional methods.     

Addition reaction of various azoles to perfluoromethyl vinyl ether

Chemistry of Heterocyclic Compounds - The addition reaction of perfluoromethyl vinyl ether to various azoles – derivatives of pyrrole, imidazole, pyrazole, indole, benzotriazole, carbazole,...     

14N nuclear quadrupole resonance in carbazoles

Nitrogen-14 nuclear quadrupole resonance frequencies at 77 K are reported for a series of carbazole compounds including N-vinylcarbazole. Differences in charge distribution between pyrrole and carbazole are explained on the basis of delocalization of pi electrons. Effects of the aldehyde and vinyl groups on charge distribution are discussed. Sigma bond polarization between the pyrrole nitrogen and the nitroso nitrogen toward the pyrrole nitrogen exists in N-nitrosocarbazole.     

Cyclization of 3-Ethoxycarbonylmethyl-, 3-Cyanomethyl-, and 3-Acetylmethyl-1-amino-2-methylbenzimidazolium Salts Effected by Acetic Anhydride in the Presence of a Base

3-Ethoxycarbonylmethyl- and 3-cyanomethyl-1-amino-2-methylbenzimidazolium chlorides cyclized at treatment with acetic anhydride in the presence of potassium carbonate to afford a mixture of derivatives of pyrazolo[1,5-a]benzimidazole and 4-aminopyrrolo[1,2-a]benzimidazole. Therewith in the first case prevails the process of pyrazole ring fusion, and in the latter pyrrole ring is fused. 3-Aroyl(thenoyl)methyl-1-amino-2-methylbenzimidazolium bromides under the same conditions are converted into 1-aroyl(thenoyl)-2-methyl- and 2-4-acetamido-3-acetylpyrrolo[1,2-a]benzimidazoles.     

Adamantylation of Imidazoles and Benzimidazole

For the first time is reported on substitution of a hydrogen atom in position 4 of the imidazole ring with an aliphatic substituent occurring in reaction between 1-bromoadamantane and imidazoles. The reaction proceeds alongside the substitution in position 1 at heating in excess imidazole. In o-dichlorobenzene solution adamantylation of benzimidazole afforded 1-(1-adamantyl)benzimidazole and 1,3-di(1-adamantyl)benzimidazolium bromide. The specific features of the reactions course are described. The structure of compounds obtained is proved by ¹H NMR spectroscopy.     

Regioselective,Unconventional Pictet–Spengler Cyclization Strategy Toward the Synthesis of Benzimidazole‐Linked Imidazoquinoxalines on a Soluble Polymer Support

A novel strategy for an unconventional Pictet–Spengler reaction has been developed for the regioselective cyclization of the imidazole ring system at the C2 position. The developed strategy was utilized to develop a diversity‐oriented parallel synthesis for bis(heterocyclic) skeletal novel analogs of benzimidazole‐linked imidazoquinoxalines on a soluble polymer support under microwave conditions. Condensation of polymer‐immobilized o‐phenylenediamines with 4‐fluoro‐3‐nitrobenzoic acid followed by nucleophilic aromatic substitution with an imidazole motif affords bis(heterocyclic) skeletal precursors for the Pictet–Spengler reaction. The unconventional Pictet–Spengler cyclization with various aldehydes was achieved regioselectively at the C2 position of the imidazole ring to furnish rare imidazole‐fused quinoxaline skeletons. During the Pictet–Spengler cyclization, aldehydes bearing electron‐donating groups afford 4,5‐dihydro‐imidazoquinoxalines, which then auto‐aromatize into benzimidazole‐linked imidazo[1,2‐a]quinoxalines. However, interestingly, aldehydes bearing electron‐withdrawing groups directly provide aromatized imidazo[1,2‐a]quinoxalines, which unexpectedly afford novel benzimidazole‐linked 4‐methoxy‐4,5‐dihydro‐imidazo[1,2‐a]quinoxalines after polymer cleavage.     

Ab initio study of azolides: Energetic and spectroscopic properties

We report the ab initio study of twenty‐four azolides derived from pyrrole, imidazole, pyrazole, both triazoles, tetrazole, pentazole, indole and carbazole bearing at the nitrogen atom the groups COMe, CHO, COCF₃ and CO₂Me. Theoretical values (isomerism, barriers, dipole moments, C=O stretching) are compared with experimental ones, when available, and also internally compared. A special effort has been devoted to the calculation of the absolute shieldings for the different nuclei present in azolides. At the level of calculation used (RHF/6‐311G**) the results are satisfactory. To complete the nmr data from the literature, some ¹H, ¹³C, ¹⁵N, ¹⁷O and 19F chemical shifts have been determined.     

含氮杂环类阴离子受体*

含氮杂环类阴离子受体是目前超分子阴离子识别领域研究的热点之一。此类受体具有主体结构丰富、可调节性强、识别范围广、选择性强、灵敏度高等优点。本文综述了以吡咯、吲哚、咪唑、吡唑等含氮杂环为识别基团的阴离子受体的设计原理、识别性能和机理,展望了该领域的发展方向。     

One-step synthesis of N-[(methylthio)methyl]imidazole and related heterocyclic derivatives via a fummerer rearrangement

N-[(Methylthio)methyl]imidazole may be prepared from dimethylsulfoxide and N-(trimethylsilyl)imidazole or N-(t-butyldimethylsilyl)imidazole at elevated temperatures via a Purnmerer rearrangement. The product was characterized by elemental analysis, mass spectrometry and proton and carbon nmr. Preliminary experiments show that corresponding derivatives of 2-methylimidazole, pyrazole, triazole and benzimidazole may also be prepared in an analogous manner.     

Cu(OAc)2·H2O-catalyzed N-arylation of nitrogen-containing heterocycles

In the absence of any additional ligands, the efficient N-arylation of nitrogen-containing heterocycles with aryl iodides catalyzed by relative low catalyst amount of Cu(OAc)₂·H₂O was developed. This simple catalytic system is involved in the C-N cross-coupling reaction and works for a variety of pyrazole, pyrrole, imidazole, triazole, indole, benzoimidazole, benzotriazole, carbazole, and anilines as well as aryl iodides with different electronic properties. Highly efficient copper(II)-catalyzed N-arylation protocol was established.     

Amino acid promoted CuI-catalyzed C-N bond formation between aryl halides and amines or N-containing heterocycles

CuI-catalyzed coupling reaction of electron-deficient aryl iodides with aliphatic primary amines occurs at 40 degrees C under the promotion of N-methylglycine. Using l-proline as the promoter, coupling reaction of aryl iodides or aryl bromides with aliphatic primary amines, aliphatic cyclic secondary amines, or electron-rich primary arylamines proceeds at 60-90 degrees C; an intramolecular coupling reaction between aryl chloride and primary amine moieties gives indoline at 70 degrees C; coupling reaction of aryl iodides with indole, pyrrole, carbazole, imidazole, or pyrazole can be carried out at 75-90 degrees C; and coupling reaction of electron-deficient aryl bromides with imidazole or pyrazole occurs at 60-90 degrees C to provide the corresponding N-aryl products in good to excellent yields. In addition, N,N-dimethylglycine promotes the coupling reaction of electron-rich aryl bromides with imidazole or pyrazole to afford the corresponding N-aryl imidazoles or pyrazoles at 110 degrees C. The possible action of amino acids in these coupling reactions is discussed.     

Synthesis and photovoltaic properties of conjugated copolymers based on benzimidazole and various thiophene

A new accepter unit, dimethyl‐2H‐benzimidazole, was prepared and used for the synthesis of the conjugated polymers containing electron donor–acceptor pair for organic photovoltaics (OPVs). Dimethyl‐2H‐benzimidazole unit was designed to substitute the BT unit of poly(N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)) (PCDTBT). A series of new semiconducting polymers with 2,2‐dimethyl‐2H‐benzimidazole, 9‐heptadecanyl‐9H‐carbazole, and thiophene (or bithiophene) units was synthesized using Stille polymerization to generate PCDTMBIs (or PCBBTMBIs). In dimethyl‐2H‐benzimidazole, the sulfur at 2‐position of BT unit was replaced with dialkyl substituted carbon, while keeping the 1,2‐quinoid form, to improve the solubility of the polymers. The absorption spectra of PCDTMBIs with thiophene units exhibit two maximum peaks at about 430 and 613–645 nm in solution. The solutions of PCBBTMBIs show two absorption peaks at about 445–456 and 630–645 nm which is red‐shifted about 20 nm when compared with PCDTMBIs caused by the introduction of bithiophene units. In most efficient polymer PCBBTMBI3, the device annealed at 100 °C for 10 min demonstrated a V_OC value of 0.60 V, a J_SC value of 4.31 mA/cm², and a FF of 0.35, leading to the power conversion efficiency (PCE) of 0.91%, under white light illumination (AM 1.5 G and 100 mW/cm²). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A novel ferrocenylalkylating reagent. Ferrocenylalkylation of imidazole and its derivatives

Reactions of α-(1-benzotriazolyl)ethylferrocene (1) with 1,2,4-triazole, imidazole, benzimidazole, and edenine have been studied in the MeOH−HCl, MeOH, and AcOH systems. Compound 1 is a novel ferrocenylalkylating reagent which, unlike α-hydroxyalkylferrocenes, is capable of alkylating imidazole, benzimidazole (even in the absence of an acid catalyst), and adenine (regioselectively at the N(3) position). The antitumor activity discovered for ferrocenylalkylazoles of the type 1 may be attributed to the ability of such compounds to ferrocenylalkylate nucleic bases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 172–174, January, 1997.     

Alternative heterocycles for DNA recognition: the benzimidazole/imidazole pair

Boc-protected benzimidazole-pyrrole, benzimidazole-imidazole, and benzimidazole-methoxypyrrole amino acids were synthesized and incorporated into DNA binding polyamides, comprised of N-methyl pyrrole and N-methyl imidazole amino acids, by means of solid-phase synthesis on an oxime resin. These hairpin polyamides were designed to determine the DNA recognition profile of a side-by-side benzimidazole/imidazole pair for the designated six base pair recognition sequence. Equilibrium association constants of the polyamide-DNA complexes were determined at two of the six base pair positions of the recognition sequence by quantitative DNase I footprinting titrations on DNA fragments each containing matched and single base pair mismatched binding sites. The results indicate that the benzimidazole-heterocycle building blocks can replace pyrrole-pyrrole, pyrrole-imidazole, and pyrrole-hydroxypyrrole constructs while retaining relative site specifities and subnanomolar match site affinities. The benzimidazole-containing hairpin polyamides represent a novel class of DNA binding ligands featuring tunable target recognition sequences combined with the favorable properties of the benzimidazole type DNA minor groove binders.     

Protonation Sites in Gaseous Pyrrole and Imidazole: A Neutralization–Reionization and ab initio Study

Mild gas-phase acids C₄H₉⁺ and NH₄⁺ protonate pyrrole at C-2 and C-3 but not at the nitrogen atom, as determined by deuterium labeling and neutralization–reionization mass spectrometry. Proton affinities in pyrrole are calculated by MP2/6–311G(2d, p) as 866, 845 and 786 kJ mol^-1 for protonation at C-2, C-3 and N, respectively. Vertical neutralization of protonated pyrrole generates bound radicals that in part dissociate by loss of hydrogen atoms. Unimolecular loss of hydrogen atom from C-2-and C-3-protonated pyrrole cations is preceded by proton migration in the ring. Protonation of gaseous imidazole is predicted to occur exclusively at the N-3 imine nitrogen to yield a stable aromatic cation. Proton affinities in imidazole are calculated as 941, 804, 791, 791 and 724 for the N-3, C-4, C-2, C-5 and N-1 positions, respectively. Radicals derived from protonated imidazole are only weakly bound. Vertical neutralization of N-3-protonated imidazole is accompanied by large Franck–Condon effects which deposit on average 183 kJ mol^-1 vibrational energy in the radicals formed. The radicals dissociate unimolecularly by loss of hydrogen atom, which involves both direct N-H bond cleavage and isomerization to the more stable C-2 H-isomer. Potential energy barriers to isomerizations and dissociations in protonated pyrrole and imidazole isomers and their radicals were investigated by ab initio calculations.     

Studies on intramolecular nh-bridging in aromatic compounds. Part 3 [1–3]

A study was made of the use of calcium oxide as a catalyst at a temperature of 400–700° for the dehy-drocyclization of four primary arylamines: 2-aminobiphenyl, 1-aminotriphenylene (5c) , 2-phenoxyaniline, and N-(2-aminophenyl)pyrrole. Maximal yields of cyclized products isolated were 53% (carbazole), 52% (4H-naphtho[1,4-def]carbazole), 18% (phenoxazine), and 0%, respectively. Comparison is made with reported cyclizations of the corresponding nitro and azido starting materials. In one case, treatment of I-nitrotriphenylene with triethyl phosphite produced mainly diethyl N-(1-triphenylenyl)phosphoramidate (51%). Mono- and hemihydrochlorides of 5c are described. A mechanism for the catalyzed dehydrocy-clization is proposed.