N-alkyl Substituents Research Articles

Critical Role of Alkyl Chain Branching of Organic Semiconductors in Enabling Solution-Processed N-Channel Organic Thin-Film Transistors with Mobility of up to 3.50 cm2 V–1 s–1

Substituted side chains are fundamental units in solution processable organic semiconductors in order to achieve a balance of close intermolecular stacking, high crystallinity, and good compatibility with different wet techniques. Based on four air-stable solution-processed naphthalene diimides fused with 2-(1,3-dithiol-2-ylidene)malononitrile groups (NDI-DTYM2) that bear branched alkyl chains with varied side-chain length and different branching position, we have carried out systematic studies on the relationship between film microstructure and charge transport in their organic thin-film transistors (OTFTs). In particular synchrotron measurements (grazing incidence X-ray diffraction and near-edge X-ray absorption fine structure) are combined with device optimization studies to probe the interplay between molecular structure, molecular packing, and OTFT mobility. It is found that the side-chain length has a moderate influence on thin-film microstructure but leads to only limited changes in OTFT performance. In contrast, the position of branching point results in subtle, yet critical changes in molecular packing and leads to dramatic differences in electron mobility ranging from ~0.001 to >3.0 cm(2) V(-1) s(-1). Incorporating a NDI-DTYM2 core with three-branched N-alkyl substituents of C(11,6) results in a dense in-plane molecular packing with an unit cell area of 127 Å(2), larger domain sizes of up to 1000 × 3000 nm(2), and an electron mobility of up to 3.50 cm(2) V(-1) s(-1), which is an unprecedented value for ambient stable n-channel solution-processed OTFTs reported to date. These results demonstrate that variation of the alkyl chain branching point is a powerful strategy for tuning of molecular packing to enable high charge transport mobilities.

Zirconium and hafnium complexes containing N-alkyl substituted amine biphenolate ligands: coordination chemistry and living ring-opening polymerization catalysis

The coordination chemistry of zirconium and hafnium complexes containing the tridentate amine biphenolate ligands [RN(CH2-2-O-3,5-C6H2(tBu)2)2](2-) ([R-ONO](2-); R = tBu (1a), iPr (1b), nPr (1c)) featuring distinct N-alkyl substituents is described. Alcoholysis of Zr(OiPr)4(HOiPr) or Hf(OiPr)4(HOiPr) with H2[1a] in diethyl ether solutions at -35 °C generates the corresponding five-coordinate [1a]M(OiPr)2 (M = Zr (2a), Hf (3a)) in high isolated yield. Similar reactions employing H2[1b] produce six-coordinate [1b]M(OiPr)2(HOiPr) (M = Zr (2b·HOiPr), Hf (3b·HOiPr)) as an isopropanol adduct. Repetitive trituration of 2b·HOiPr and 3b·HOiPr with diethyl ether gives five-coordinate 2b and 3b, respectively. Treatment of M(OiPr)4(HOiPr) with H2[1c] under similar conditions affords six-coordinate [1c]M(OiPr)2(HOiPr) (M = Zr (2c·HOiPr), Hf (3c·HOiPr)), subsequent recrystallization of which from acetonitrile-diethyl ether solutions leads to acetonitrile adducts 2c·MeCN and 3c·MeCN. Reactivity studies of these zirconium and hafnium complexes revealed that they are all active catalysts for ring-opening polymerization of ε-caprolactone. Among them, the N-isopropyl derived complexes are most reactive. Polymerizations catalyzed by 2b, 3b and 3c·MeCN were proved to be living. The X-ray structures of 2a·HOiPr, 2a·MeCN, 2c·HOiPr, 2c·MeCN, and 3c·MeCN are presented.

Optimizing the formation of 2,6-bis(N-alkyl-benzimidazolyl)pyridine-containing [3]catenates through component design

The 2,6-bis(N-alkyl-benzimidazolyl)pyridine (Bip) ligand has been utilized to access mechanically interlocked [3]catenanes via metal-templating. Components containing the Bip ligand, namely macrocycles and linear threads, were designed to self-assemble upon the addition of transition metal ions into [3]metallopseudorotaxanes that require a single olefin metathesis reaction to yield the [3]catenate. Utilizing two-dimensional diffusion-ordered NMR spectroscopy (DOSY) the crude reaction mixture resulting from the ring-closing reaction of this template was studied. It was shown that the yield of the [3]catenates was dependent on the preorganization and conformational flexibility of the thread-like component and the size of the N-alkyl substituents on the Bip in the macrocyclic component. Through judicious design of both components the resulting reaction distribution can be altered to predominantly favour the formation of the [3]catenate. Furthermore, after de-metalation and purification the resulting [3]catenanes were fully characterized by a variety of NMR and mass spectroscopy techniques.

N-alkyl functionalised expanded ring N-heterocyclic carbene complexes of rhodium(i) and iridium(i): structural investigations and preliminary catalytic evaluation

A series of new N-alkyl functionalised 6- and 7-membered expanded ring N-heterocyclic carbene (NHC) pro-ligands 3-6 and their corresponding complexes of rhodium(I) and iridium(I), [M(NHC)(COD)Cl] 7-14 and [M(NHC)(CO)2Cl] 15-22 are described. The complexes have been characterised by (1)H and (13)C{(1)H} NMR, mass spectrometry, IR and X-ray diffraction. It is noted from X-ray diffraction studies that the N-alkyl substituents are found to orientate themselves away from the metal centre due to unfavourable steric interactions resulting in low percent buried volume (%V(bur)) values in the solid state. The heterocycle ring size is also found to dictate the spatial orientation of the N-alkyl substituents in the neopentyl functionalised derivatives 10 and 14. The 7-membered derivative 14 allows for a conformational 'twist' of the heterocycle ring with the N-alkyl substituents adopting a mutually trans configuration with respect to each other, while the more rigid 6-membered system 10 does not allow for this conformational 'twist' and consequently the N-alkyl substituents adopt a mutually cis configuration. The σ-donor function of this new class of expanded ring NHC ligand has also been probed by measured IR stretching frequencies of the [M(NHC)(CO)2Cl] complexes 15-22. A preliminary catalytic survey of the hydrogenation of functionalised alkenes with molecular hydrogen under mild conditions has also been undertaken with complex , affording an insight into the application of large ring NHC ancillary ligands bearing N-alkyl substituents in hydrogenation transformations.

ChemInform Abstract: Synthesis of Chiral β‐Amino Acid Derivatives by Asymmetric Hydrosilylation with an Imidazole Derived Organocatalyst.

The organocatalysed asymmetric hydrosilylation of a number of N-aryl and alkyl β-substituted enamino esters proceeds in generally good yield and enantioselectivity. Crucial to obtaining high yield and selectivity was the addition of benzoic acid as an additive and under these conditions, both N-alkyl and N-aryl substituents were well tolerated. β-Aryl and alkyl substituents were evaluated and a model proposed to account for the experimental observations based upon enamine tautomerisation and conformational preferences of the reactive ketimine intermediate.

13C NMR identification in crude oils of hydrocarbons bearing ethyl and n-alkyl substituents on their main chain

Assignment of 13C NMR signals of compounds with ethyl, n-propyl, n-butyl, n-amyl, and n-C6+ alkyl substituents in different positions of carbon chains in the spectra of saturated hydrocarbon fractions of crude oils and in the spectra of crude oils, taking into account the dependence of chemical shifts on the recording temperature, the concentration of the test solution. and the composition of the object of study, has been proposed. The capabilities of the 13C NMR technique as applied to determination of this almost unexplored group of hydrocarbons in crude oils have been discussed.

Bithiopheneimide–Dithienosilole/Dithienogermole Copolymers for Efficient Solar Cells: Information from Structure–Property–Device Performance Correlations and Comparison to Thieno[3,4-c]pyrrole-4,6-dione Analogues

Rational creation of polymeric semiconductors from novel building blocks is critical to polymer solar cell (PSC) development. We report a new series of bithiopheneimide-based donor-acceptor copolymers for bulk-heterojunction (BHJ) PSCs. The bithiopheneimide electron-deficiency compresses polymer bandgaps and lowers the HOMOs--essential to maximize power conversion efficiency (PCE). While the dithiophene bridge progression R(2)Si→R(2)Ge minimally impacts bandgaps, it substantially alters the HOMO energies. Furthermore, imide N-substituent variation has negligible impact on polymer opto-electrical properties, but greatly affects solubility and microstructure. Grazing incidence wide-angle X-ray scattering (GIWAXS) indicates that branched N-alkyl substituents increased polymer π-π spacings vs linear N-alkyl substituents, and the dithienosilole-based PBTISi series exhibits more ordered packing than the dithienogermole-based PBTIGe analogues. Further insights into structure-property-device performance correlations are provided by a thieno[3,4-c]pyrrole-4,6-dione (TPD)-dithienosilole copolymer PTPDSi. DFT computation and optical spectroscopy show that the TPD-based polymers achieve greater subunit-subunit coplanarity via intramolecular (thienyl)S···O(carbonyl) interactions, and GIWAXS indicates that PBTISi-C8 has lower lamellar ordering, but closer π-π spacing than does the TPD-based analogue. Inverted BHJ solar cells using bithiopheneimide-based polymer as donor and PC(71)BM as acceptor exhibit promising device performance with PCEs up to 6.41% and V(oc) > 0.80 V. In analogous cells, the TPD analogue exhibits 0.08 V higher V(oc) with an enhanced PCE of 6.83%, mainly attributable to the lower-lying HOMO induced by the higher imide group density. These results demonstrate the potential of BTI-based polymers for high-performance solar cells, and provide generalizable insights into structure-property relationships in TPD, BTI, and related polymer semiconductors.

Exploring the PDE5 H-pocket by ensemble docking and structure-based design and synthesis of novel β-carboline derivatives

By studying the co-crystal information of interactions between PDE5 and its inhibitors, forty new tetrahydro-β-carbolines based-analogues were synthesized, and tested for their PDE5 inhibition. Some compounds were as active as tadalafil in inhibiting PDE5 and of better selectivity profile particularly versus PDE11A, the nature of the terminal ring and its nitrogen substituent are the main determinants of selectivity. Ensemble docking confirmed the role of H-loop closed conformer in activity versus its occluded and open forms. Conformational studies showed the effect of bulkiness of the terminal ring N-alkyl substituent on the formation of stable enzyme ligands conformers. The difference in potencies of hydantoin and piperazinedione analogues, together with the necessity of C-5/C-6 R-absolute configuration has been revealed through molecular docking.

Preorganization of diglycolamides on the calix[4]arene platform and its effect on the extraction of Am(III)/Eu(III)

Different diglycolamide (DGA)-substituted calix[4]arene-based extractants were synthesized and evaluated for the extraction of Am(III) and Eu(III), representative trivalent actinide and lanthanide ions, respectively. On the narrow rim of the calix[4]arene platform, the DGA moiety was either 1,3-di- or tetrasubstituted with a varying spacer length between the oxygen and amide nitrogen atom. In addition, DGA groups were appended both to the wide rim and to both rims of calix[4]arenes and their efficiencies were compared for Am(III) and Eu(III) extraction at three different feed acidities. The extraction and separation efficiencies strongly depended on the N-alkyl substituent as well as the spacer length. 1,3-Di-DGA-substituted calix[4]arenes are inferior extractants to the corresponding tetra-DGA-substituted ones. Narrow rim DGA-functionalized derivatives resulted in high extraction efficiencies, while the wide rim DGA-functionalized calix[4]arenes showed practically no extraction.

Lithium complexes of tridentate amine biphenolate ligands containing distinct N-alkyl substituents

Deprotonation of neutral amine biphenol compounds H2[R-ONO]([R-ONO]2−=[RN(CH2-2-O-3,5-C6H2(tBu)2)2]2−; R=tBu (1a), iPr (1b), nPr (1c)) with 2equiv. of n-BuLi in 1,2-dimethoxyethane (DME) at −35°C produces colorless crystalline [{Li2(1a)(DME)}2(μ-DME)] (2a), [Li2(1b)(DME)2] (2b), and [{Li2(1c)(DME)}2(μ-DME)] (2c), respectively. X-ray diffraction studies of both 2a and 2c showed them to be tetra-nuclear species containing two Li2(1a)(η2-DME) or Li2(1c)(η2-DME) subunits linked with a bridging DME whereas that of 2b revealed a binuclear constitution composed of one Li2(1b)(η2-DME) unit and an additional η1-bound DME. These complexes undergo rapid fluxional exchange in solutions as indicated by variable temperature 1H and 7Li{1H} NMR studies. Complexes 2a, 2b, and 2c are all active catalysts for ring-opening polymerization of ε-caprolactone.

Carbon, Hydrogen, and Nitrogen Isotope Fractionation Associated with Oxidative Transformation of Substituted Aromatic N-Alkyl Amines

We investigated the mechanisms and isotope effects associated with the N-dealkylation and N-atom oxidation of substituted N-methyl- and N,N-dimethylanilines to identify isotope fractionation trends for the assessment of oxidations of aromatic N-alkyl moieties by compound-specific isotope analysis (CSIA). In laboratory batch model systems, we determined the C, H, and N isotope enrichment factors for the oxidation by MnO(2) and horseradish peroxidase (HRP), derived apparent (13)C-, (2)H-, and (15)N-kinetic isotope effects (AKIEs), and characterized reaction products. The N-atom oxidation pathway leading to radical coupling products typically exhibited inverse (15)N-AKIEs (up to 0.991) and only minor (13)C- and (2)H-AKIEs. Oxidative N-dealkylation, in contrast, was subject to large normal (13)C- and (2)H-AKIEs (up to 1.019 and 3.1, respectively) and small (15)N-AKIEs. Subtle changes of the compound's electronic properties due to different types of aromatic and/or N-alkyl substituents resulted in changes of reaction mechanisms, rate-limiting step(s), and thus isotope fractionation trends. The complex sequence of electron and proton transfers during the oxidative transformation of substituted aromatic N-alkyl amines suggests highly compound- and mechanism-dependent isotope effects precluding extrapolations to other organic micropollutants reacting along the same degradation pathways.

Synthesis of chiral β-amino acid derivatives by asymmetric hydrosilylation with an imidazole derived organocatalyst

The organocatalysed asymmetric hydrosilylation of a number of N-aryl and alkyl β-substituted enamino esters proceeds in generally good yield and enantioselectivity. Crucial to obtaining high yield and selectivity was the addition of benzoic acid as an additive and under these conditions, both N-alkyl and N-aryl substituents were well tolerated. β-Aryl and alkyl substituents were evaluated and a model proposed to account for the experimental observations based upon enamine tautomerisation and conformational preferences of the reactive ketimine intermediate.

Incorporation of pyrrole to oligothiophene-based quinoids endcapped with dicyanomethylene: a new class of solution processable n-channel organic semiconductors for air-stable organic field-effect transistors

We report the synthesis and characterization of a novel series of pyrrole-containing quinoids endcapped with dicyanomethylene groups. The modification of the quinoidal core structure through incorporating pyrrole unit presents two main advantages: firstly, N-alkyl substituents of pyrrole can serve as solubilizing groups for the realization of solution-processability; secondly, the variation of N-alkyl substituents is easily achieved and thus greatly enriches the number of species in such a series of materials. Additionally, the retained quinoidal core structure as well as the electron-withdrawing endcapped group ensures a sufficiently low LUMO energy level (ca. 4.30–4.39 eV below the vacuum level), meeting the requirement for air-stable n-channel organic semiconductors. X-ray crystallographic data of 3b reveals that except for the branched alkyl substituent, the whole molecule shows high planarity by assuming a rarely observed syn conformation. Solution-processed OFETs based on such pyrrole-containing quinoids showed typical n-channel FET characteristics under ambient conditions, with a maximum electron mobility up to 0.014 cm2 V−1 s−1 and Ion/Ioff values of ca. 104, indicating that this series of materials are promising candidates for solution processable n-channel semiconductors, and adopting a pyrrole moiety to the construct the quinoidal core structure provides an efficient approach to the development of novel n-channel organic semiconductors.

Electronic effects in 1,3-dipolar cycloaddition reactions of N-alkyl and N-benzyl nitrones with dipolarophiles

1,3-Dipolar cycloadditions afforded fast access to isoxazolidines bearing N-alkyl or N-benzyl substituents. The electronic properties of the substituents in the nitrones define the activity of the dipoles and modulate diastereoselectivity in the non-catalyzed reactions. Using a chiral one-point binding ruthenium Lewis acid catalyst, products were obtained in good yields and with excellent regio-, diastereo-, and enantioselectivity.

Self-Assembly of Silver(I) and Gold(I) N-Heterocyclic Carbene Complexes in Solid State, Mesophase, and Solution

The assembly of silver(I) and gold(I) complexes of functionalized N-heterocyclic carbenes (NHCs) of the type [M(C(n),amide-imy)(2)][anion] were studied, in which C(n),amide-imy stands for an NHC of imidazol-2-ylidene having one N-alkyl substituent (C(n)H(2n+1)) and one N-acetamido substituent, while the anions are Br(-), NO(3)(-), BF(4)(-) or PF(6)(-). A single crystal X-ray diffraction study reveals that self-assembly of [Ag(C(10),amide-imy)(2)][PF(6)] through Coulombic, hydrogen bonding, and hydrophobic interactions gives a lamellar structure with tubular architecture around the metal ion head core. Self-assembly of these functionalized NHC complexes also leads to the formation of the first example of thermotropic liquid crystals of silver(I)-NHCs and gels of gold(I)-NHC. Results from an infrared spectroscopy study show that the degree of chain motion in the gel state is smaller than that in the mesophase, yet comparable to that in the solid state. In addition, the technique of nuclear magnetic resonance diffusion ordered spectroscopy was found for the first time to be a good tool to study the phase transition of gels. Xerogels of gold(I)-NHCs display fibers, oriental lantern-shaped bundles of belts and helical fibers when observed under scanning electron and transmission electron microscopes.

Synthesis of Mono- and Bis-N-Heterocyclic Carbene Copper(I) Complexes via Decarboxylative Generation of Carbenes

Zwitterionic carboxylates can be thermally decarboxylated in the presence of copper salts to form NHC-copper com­plexes. The selective formation of either mono- or bis-NHC complexes is possible through simple control of the molar equivalents of the copper salt. A variety of different NHC ligands with either saturated or unsaturated backbones or bearing N-aryl or N-alkyl substituents can be complexed to copper.

O,O′-Disubstituted N,N′-Dihydroxynaphthalenediimides (DHNDI): First Principles Designed Organic Building Blocks for Materials Science

N,N'-Disubstituted naphthalenediimides (NDIs), planar, electron-deficient building blocks, play an important role in materials and biological sciences. Naphthalene core substituents control the HOMO and LUMO energies, whereas the N-alkyl or aryl substituents affect the solubility, aggregation, and packing propensity in condensed phases. N,N'-Dihydroxynaphthalenediimide (DHNDI) allows expanding the chemical diversity by O-alkylation, acylation, or sulfonylation; these derivatives also allow fine-tuning of the HOMO/LUMO levels. The synthesis, UV-vis, electrochemical, solid state, and computational prediction of the properties of such derivatives are presented.

N-Heterocyclic Carbene-Amide Rhodium(I) Complexes: Structures, Dynamics, and Catalysis

The amide-functionalized imidazolium salts [BocNHCH2CH2ImR]X (R = Me, X = I, 1a; R = benzyl, X = Br, 1b; R = trityl, X = Cl, 1c) bearing increasingly bulky N-alkyl substituents were prepared in high yields by direct alkylation of the (2-imidazol-1-yl-ethyl)carbamic acid tert-butyl ester; 1c is a crystalline solid also characterized by X-ray diffraction. These salts are precursors for the synthesis of rhodium(I) complexes [Rh(NBD)X(NHC)] (NHC = 1-(2-NHBoc-ethyl)-3-R-imidazolin-2-ylidene; X = Cl, R = Me (3a), R = benzyl (3b), R = trityl (3c); X = I, R = Me (4a)). All the complexes display restricted rotation about the metal–carbene bond; however, while the rotation barriers calculated for 3a,b and 4a matched the experimental values, unexpectedly this was not true in the case of 3c, where the experimental value was equal to that obtained for compound 3b (58.6 kJ mol–1) and much smaller with respect to the calculated one (100.0 kJ mol–1). The catalytic activity of the neutral rhodium(I) complexes 3a–c in the ...

Amide isosteres in structure-activity studies of antibacterial minor groove binders

Antibacterial minor groove binders related to the natural product, distamycin, are development candidates for novel antibiotics. Alkenes have been found to be effective substitutes for the isosteric amide links in some positions and alkyl groups larger than methyl have been found to increase binding to DNA in both selectivity and affinity. However the impact of other isosteres such as diazenes and the position of an alkyl group with respect to DNA binding and antibacterial activity are not known. The effects of some systematic variations in the structure of polyamide minor groove binders are investigated. Isosteres of the amide link (alkenes and diazenes) are compared: it is shown that all three are competent for binding to DNA but that alkene links give the tightest binding and highest antibacterial activity; no significant antibacterial activity was found for compounds with a diazene link. Within a series of alkene linked compounds, the effect of branched N-alkyl substituents on binding to DNA and antibacterial activity is investigated: it was found that C3 and C4 branched chains are acceptable at the central pyrrole residue but that at the pyrrole ring adjacent to the basic tail group, a C4 branched chain was too large both for DNA binding and for antibacterial activity. The active branched alkyl chain compounds were found to be especially active against Mycobacterium aurum, a bacterium related to the causative agent of tuberculosis.

A structure–function study of the surface tension changes of m-xylene in the presence of fluorous 1H-1,2,3-triazoles and tetrazoles

A study of surface tension measurements in m-xylene has shown that new hybrid 1H-1,2,3-triazoles and tetrazoles bearing perfluoroalkylethyl and -methyl substituents in combination with n-alkyl (lipophilic), n-alkoxymethyl (mildly hydrophilic), or methoxy(triethylenoxy)methyl (hydrophilic) substituents do have considerable surfactant properties. The properties of those with lipophilic substituents, especially those with alkyl chains of 8 carbons (or possibly more) border on erratic, while those with mildly hydrophilic or hydrophilic substituents exhibit highly predictable behaviour that is consistent with current understanding of surfactants. The change from two methylene spacer groups (perfluoroalkylethyl) to one methylene spacer group (perfluoroalkylmethyl) [equal to increasing the fluorine content], and the change from triazole to tetrazole nucleus, impart very significant increases on surface activity, whereas increases in the chain length of n-alkyl or perfluoroalkyl substituents have incremental effects.