CN Substituents Research Articles

Synthesis, structure, and properties of luminescent diazaborole and indole systems

Thiophenes and phenylacetylenes, decorated with 1-methylindol-2-yl, 1,3,2-benzodiazaborol-2-yl, 1,3,2-diazaborol-2-yl, or 1,3,2-diazaborolidinyl groups at one end and dimesitylborolyl or CN substituents at the opposite end of the molecules, were synthesized. Upon UV irradiation, these push-pull systems in THF solution gave rise to bright-blue emission with Stokes shifts ranging from 4100 to 9300 cm–1 and quantum efficiencies up to 0.99. Thereby intramolecular charge transfer took place from the HOMO of the indolyl or borolyl fluorophores to the LUMO, mainly centered on the electron-withdrawing cyano or dimesitylboranyl group.

Design, synthesis and anti-P. falciparum activity of pyrazolopyridine–sulfonamide derivatives

Ten 1-phenyl-1H-pyrazolo[3,4-b]pyridine derivatives connected by a linker group to benzenesulfonamide moieties with different substituents in the 4-position were synthesized and assayed against Plasmodium falciparum. These ten compounds exhibited activity in vitro against the chloroquine-resistant clone W2 with IC50 values ranging from 3.46 to 9.30μM. The most active derivatives with substituent R2=Cl or CH3 at the benzenesulfonamide moiety exhibited the lowest IC50. Compounds with an R1=CO2Et substituent at the 5-position of the 1H-pyrazolo[3,4-b]pyridine ring presented lower activity than those with a CN substituent. The 1H-pyrazolo[3,4-b]pyridine system appears to be promising for further studies as an antimalarial for overcoming the burden of resistance in P. falciparum.

Design of Acceptors with Suitable Frontier Molecular Orbitals to Match Donors via Substitutions on Perylene Diimide for Organic Solar Cells.

A series of perylene diimide (PDI) derivatives have been investigated at the CAM-B3LYP/6-31G(d) and the TD-B3LYP/6-31+G(d,p) levels to design solar cell acceptors with high performance in areas such as suitable frontier molecular orbital (FMO) energies to match oligo(thienylenevinylene) derivatives and improved charge transfer properties. The calculated results reveal that the substituents slightly affect the distribution patterns of FMOs for PDI-BI. The electron withdrawing group substituents decrease the FMO energies of PDI-BI, and the electron donating group substituents slightly affect the FMO energies of PDI-BI. The di-electron withdrawing group substituents can tune the FMOs of PDI-BI to be more suitable for the oligo(thienylenevinylene) derivatives. The electron withdrawing group substituents result in red shifts of absorption spectra and electron donating group substituents result in blue shifts for PDI-BI. The –CN substituent can improve the electron transport properties of PDI-BI. The –CH3 group in different positions slightly affects the electron transport properties of PDI-BI.

Chemical Bond Stabilization and Exciton Management by CN Modified Host Material for Improved Efficiency and Lifetime in Blue Phosphorescent Organic Light‐Emitting Diodes

A high triplet energy host material for improved efficiency and elongated lifetime is developed by modifying carbazole linked terphenyl with a CN substituent. The CN modification strengthens electron injection and transport of the host material, which reduces the driving voltage, improved quantum efficiency, and power efficiency of blue phosphorescent organic light‐emitting diodes. Furthermore, the CN modification also extends the lifetime of the blue device due to the chemical bond stabilizing effect of the CN moiety in radical, anion, and cation states. Therefore, the molecular design modifying the backbone structure with CN is an efficient approach for high efficiency and long lifetime.

TTF-DDQ: Two “green” synthetic routes, crystal structure and band gap from FT-IR spectroscopy

TTF-DDQ (DDQ=2,3-dichloro-5,6-dicyano-p-benzoquinone) is an ionic and diamagnetic charge transfer salt. Polycrystalline powders of TTF-DDQ were obtained by three synthetic methods: solvent evaporation from MeCN solution (1), MeCN vapor digestion (2), and mechanochemistry (liquid assisted grinding with DMSO) (3). The analysis of the synchrotron X-ray powder diffraction data of 1 afforded the crystal structure, which is isomorphous to that of the black polymorph of TTF-CA (CA=chloranil). TTF-DDQ is composed of (TTF+)2 and (DDQ−)2 dimeric radical ions arranged in segregated columnar stacks, linked by weak hydrogen bonds. The Cl and CN substituents in DDQ are disordered, and this was modeled by Rietveld analysis.The FT-IR absorption spectra as a function of the temperature in the 300–10K interval showed an absorption edge, indicating that TTF-DDQ is a semiconductor with a small band gap of (0.21±0.01)eV. The monotonous evolution of the FT-IR spectra denotes the absence of crystallographic phase transitions in the temperature interval studied, likely due to the thermodynamic stability of this packing motif compared to the less stable donor-acceptor alternating stacks; or the segregated, potentially conducting stacks.

Theoretical investigations of the electronic structures of carbazole-based triphenylphosphine oxide derivatives, potential bipolar host materials in blue-phosphorescent devices.

Density functional theory calculations were performed to investigate the electronic structures of bipolar host materials comprising a backbone of linked acceptor moieties where each acceptor was also linked to a pendant donor moiety. The acceptor was triphenylphosphine oxide with two of its phenyls substituted with fluorine atoms or nitrile groups (CN). The donor was carbazole (CZ) substituted, or not, with t-butyl groups. The HOMO and LUMO energy levels of these host molecules were mainly influenced by their respective hole- and electron-transport units. The t-butyl substituents on the CZ moieties had an adverse effect on the triplet energies (E T) of the host molecules, especially for molecules where the phenyls of the backbone chain were substituted with CN groups. While introducing CN substituents onto the backbone chain decreased the energy difference between the lowest singlet and triplet excited states (ΔE ST), it also caused the energy gap between the HOMO and LUMO to narrow. Among the host molecules investigated, that in which one of the phenyls in the acceptor moiety was linked to the donor while the other two phenyls in the acceptor were substituted with CN substituents exhibited the highest E T, balanced charge transport, a low charge-injection barrier, and a small ΔE ST, and is therefore a promising candidate host material for use in blue-phosphorescent devices. Graphical Abstract Density functional theory calculations were performed to explore the electronic properties of bipolar host materials comprising a backbone of linked acceptor moieties where each acceptor was also linked to a pendant donor moiety. All of the designed molecules with high triplet energies were found to be suitable for use as host materials when matched with a blue-light guest material. The results demonstrate that the host molecule in which one of the phenyls in the triphenylphosphine oxide acceptor moiety was linked to the carbazole donor while the other two phenyls in the acceptor moiety were substituted with CN substituents yields the highest blue-phosphorescent device performance, as this host molecule has interesting features such as a high E T, balanced charge transport, a low charge-injection barrier, and a small ΔE ST.

Synthesis, antitumor activity, and structure-activity relationship of some benzo[a]pyrano[2,3-c]phenazine derivatives.

A series of benzo[a]pyrano[2,3-c]phenazine derivatives with a wide range of substitutions at ring C of the benzophenazine were designed and synthesized using the one-pot, four-component domino reactions. The targeted compounds were evaluated for their antitumor activities against HCT116, MCF7, HepG2 and A549 cancer cell lines in vitro. The most active compound 6{1,2,1,9} featured the CN and p-dimethylamino phenyl substituents on γ-pyran structure on ring C. Significantly, compound 6{1,2,1,9} was found to have the highest growth inhibitory activity against the HepG2 cell line with IC50 values of 6.71 µM, which was 1.6-fold more potent than positive control anticancer drug Hydroxycamptothecine (HCPT). Furthermore, structure-activity relationship (SAR) studies on the substitutions at ring C were discussed in details.

Expanding the family of C,N-chelated organotin(IV) pseudohalides: Synthesis and structural characterization

A set of tri- and diorganotin(IV) pseudohalides bearing the 2-(N,N-dimethylaminomethyl)phenyl-as a C,N-chelating ligand (LCN) has been prepared and structurally characterized. Triorganotin(IV) pseudohalides of the type LCNR2SnX [R = n-Bu, X = NCO (1a), NCS (1b), NCSe (1c), CN (1d); R = Ph, X = NCO (2a), NCS (2b), NCSe (2c), CN (2d)] and (LCN)2(n-Bu)SnX [X = NCO (3a), NCS (3b), NCSe (3c), CN (3d)] are monomeric both in solution and the solid state. The central tin atom in these species is five-coordinated in the solid state with distorted trigonal bipyramidal geometry. Monomeric diorganotin(IV) pseudohalides of the type (LCN)2SnX2 [X = NCO (4a), NCS (4b), NCSe (4c), CN (4d)] contain six-coordinated tin atoms with heavily distorted octahedral geometry both in solution and solid state due to the presence of two LCN units. Finally, we have found that LCN(n-Bu)Sn(NCS)2 (5) is presumably dimeric in CDCl3 and monomeric in THF-d8 or DMSO-d6 solution while it forms infinite linear polymer in the solid state via thiocyanate bridges. According to IR, multinuclear NMR spectroscopy and XRD analysis, it was found that the pseudohalide ligands of the NCY type (Y=O, S, Se) are bound via nitrogen while the CN substituent act as a common cyanide ligand (i.e. binds via carbon). DFT calculations were performed for selected compounds (2a, 2b, 2d and 4d) to further support our conclusions about the nature of the Sn-pseudohalide bonds. Compound LCNSnPhI2 (6), which was prepared in the scope of this work as well has a trigonal bipyramidal structure with non-equivalent iodine atoms.

Influence of substituents on the nature of metal⋯π interaction and its cooperativity with halogen bond.

High-level quantum chemical calculations have been performed to investigate the influence of substituents on the metal-π interaction and its cooperative effect with halogen bond in C2X4⋯MCN⋯ClF (X = H, CN, CH3; M = Cu, Ag, Au). The strong electron-withdrawing group CN weakens the metal-π covalent interaction, while the weak electron-withdrawing group CH3 strengthens it. The metal-π covalent interaction is dominated by electrostatic energy although the AuCN complex has approximately equal electrostatic and polarization contributions. However, the metal-π covalent interaction is governed by polarization energy due to the CN substitution. A cooperative effect is found for the halogen bond and metal-π interactions in C2H4⋯MCN⋯ClF, while a diminutive effect occurs in the triads by the CN substituent. Orbital interaction analysis indicates that the strong electron-withdrawing group CN causes the C=C group vary from a stronger donor orbital to a stronger acceptor orbital.

A theoretical study of substituted indeno[1,2-b]fluorene compounds and their possible applications in solar cells

This contribution mainly describes the theoretical computations based on density functional theory (DFT), of the anti-aromatic system indeno[1,2-b]fluorene with the aim of understanding the electronic effects of the substituting electron donating and electron withdrawing groups in the 6,12-positions, to investigate their potential role as sensitizers in solar cells devices. Ground state potential energy surfaces were obtained employing the B3LYP/6-31+G(d,p) theoretical level. The low energy electronic transitions were investigated through the TD-DFT method. It was possible to conclude that indeno[1,2-b]fluorine with NH2, NO2, CN substituents are the best candidates to act as light harvesting and sensitizers in solar cells.

Synthesis and Characterization of Nanobuilding Blocks [o-RStyrPhSiO1.5]10,12 (R = Me, MeO, NBoc, and CN). Unexpected Photophysical Properties Arising from Apparent Asymmetric Cage Functionalization as Supported by Modeling Studies

The photophysics of [o-4-RStyrPhSiO1.5]8 [R = Me, OMe, NBoc, and CN] was reported previously. Here we report studies on [o-4-RStyrPhSiO1.5]10,12, [o-4-RStyrPhSiO1.5]3–[PhSiO1.5]7, and [o-4-RStyrPhSiO1.5]6[PhSiO1.5]6 to explore cage size, geometry, and partial substitution effects on photophysical properties. All compounds were characterized by traditional methods including solution spectroscpy and two-photon absorption (TPA) cross sections and except R = NBoc offer Td5% ≥ 400 °C/air. All exhibit absorption and emission spectra similar to the T8 cages but with some important differences in TPA cross sections. The R-stilbenes appear to interact in the excited state through the cage, exhibiting emission spectra red-shifted from the parent stilbenes. TPA studies show novel behavior that is functional group, geometry, and substitution number dependent. Thus, NBoc TPA cross sections/moiety increase, with decreasing numbers of functional groups from 8 to 3 for PhT10 and 10 to 6 for PhT12 where [NBocStyrPhSiO1.5]8 TPA/moiety ≈0. In contrast, CN cages offer TPA/moiety values slightly greater on going from 3 to 8 (PhT10) and 6 to 10 (PhT12). NBoc TPA data are best explained if bromination occurs asymmetrically, leading to asymmetric functionalization and exceptional polarization in partially substituted cages as symmetrically substituted cages exhibit opposing polarizations. In sum, all the individual induced transition dipoles on excitation mutually cancel. In contrast, both the cage and CN are strongly electron withdrawing such that no significant polarization is observed/expected when asymmetrically functionalized. Both NBoC and CN substituents offer red shifts greater than Me and MeO T10,12, suggesting extended conjugation without polarization. Asymmetric bromination is supported by DFT modeling studies where initial o-Br/o-H bonding stabilizes incoming Br2 by 300 mEv.

Electronic Structure and Charge Transport Properties of a Series of 3,6-(Diphenyl)-s-tetrazine Derivatives: Are They Suitable Candidates for Molecular Electronics?

Optoelectronic and charge-transport related properties of a series of 3,6-diphenyl-s-tetrazine derivatives, including F, Cl, Br, and CN substituents, have been analyzed. The molecular structure and electronic properties of the new fluorine-containing derivative, bis(3,6-difluorophenyl)-s-tetrazine, were explored by spectroscopic, electrochemical, and theoretical methods. The effects of the substituent on the pristine compound have been assessed from a theoretical perspective, showing that the fluorinated and brominated derivatives have the highest predicted electron mobilities, whereas the cyano derivative is foreseen to undergo the most efficient electron injection process.

The effect of CN-substitution on the electronic and photophysical properties of bis(carbene) Ir(III) complexes containing 2-(1H-pyrazol-5-yl)pyridinato ancillary ligand: A theoretical perspective

The electronic structures and photophysical properties of four heteroleptic Ir(III) complexes 1 [(Mepmi)2Ir(pypz)], 2 [(CNpmi)(Mepmi)Ir(pypz)], 3 [(Mepmi)(CNpmi)Ir(pypz)] and 4 [(CNpmi)2Ir(pypz)] (where Mepmi=1-(4-methyl-phenyl)-3-methylimdazolin-2-ylidene-C,C2′; CNpmi=1-(4-cyano-phenyl)-3-methylimdazolin-2-ylidene-C,C2′; pypz=2-(1H-pyrazol-5-yl)pyridinato) are investigated using the density functional method. The influence of different positions and numbers of CN-substitution has been explored. The calculated results reveal that the introduction of CN substituent leads to lowered HOMO and LUMO energy levels, increased HOMO–LUMO energy gaps, and the enhanced intensity of the absorption spectra. Meanwhile, the CN-substitution in carbene ligand is found to be an efficient approach of tuning the emitting color. The one CN substituent in 2 leads to an obvious blue shift of emission spectra, while a slight red shift is observed for the 3 and 4 in comparison with 1. The qualitative analysis on the quantum yields of four complexes has been carried out with the assistance of ΔES1−T1 (singlet–triplet energy splitting), MLCT% (metal-based charge transfer contribution in T1 state) and μS1 (S0→S1 transition electric dipole moment). It showed that the designed complex 2 and 3 with one CN substituent in carbene ligand may be the potential blue-emitting materials and possess high quantum efficiency.

Anti‐Tuberculosis Evaluation and Conformational Study of N‐Acylhydrazones Containing the Thiophene Nucleus

A series of N-acylhydrazonyl-thienyl derivatives (compounds 2 and 3), mainly of the type 2-(aryl-CH=N-NHCOCH2 )-thiene (2: aryl = substituted-phenyl; 3: aryl = heteroaryl) were evaluated against Mycobacterium tuberculosis. Particularly active compound was 3 (heteroaryl = 5-nitrothien-2-yl or 5-nitrofuran-2-yl) with MIC values of 8.5 and 9.0 μM, respectively. Moderately active compounds were compound 3 (heteroaryl = pyridin-2-yl) and compound 2 containing aryl = 2- or 4-hydroxyphenyl groups, with MIC values between 170 and 408 μM. Compound 2 containing OMe, H, F, Cl, Br, CN, and NO2 substituents and compound 3 (heteroaryl = furan-2-yl, thien-2-yl, pyrrol-2-yl, imidazol-2-yl, pyridin-3-yl, and pyridin-4-yl) were all inactive. Clearly, there is no correlation of activity with the electronic effects of the substituents. The activities suggest different modes of biological action of the compounds having nitro-heteroaryl groups, on the one hand, and the 2-hydroxyphenyl or pyridin-2-yl substituents, on the other hand. Compounds having 2- or 4-hydroxyphenyl, 2-hydroxy-5-nitrophenyl, or 4-hydroxy-3-chlorophenyl were less cytotoxic than ethambutol. It is important to notice that compound 3 (aryl = 5-NO2 -furan-2-yl) exhibited a promising therapeutic index (TI = 1093.90), with a value 4.4 less than that of ethambutol. Compounds 2 and 3 exist in DMSO or MeOD solutions as mixtures of EC(O)N /EC=N and ZC(O)N /EC=N conformers.

In vitro antimalarial activity, β-haematin inhibition and structure–activity relationships in a series of quinoline triazoles

A novel series of quinoline triazole amide analogues (38–51) has been synthesized. Analogues 38–44 had a Cl substituent at the 7-position of the quinoline ring, while 45–51 had a CN substituent at this position. Compounds 40, 45 and 49 were found to be the most active in the series against the Plasmodium falciparum chloroquine-sensitive D10 strain, with IC50 values in the range of 349–1247 nM, with 40 and 45, but not 49 also exhibiting similar activity against the chloroquine-resistant K1 strain of parasite. Quinoline triazoles 40 and 44 were the most active β-haematin inhibitors, with 50% inhibitory concentrations of 14.7 and 8.9 μM respectively. In vitro antimalarial activity of the 7-Cl bearing analogues 38–44 exhibited a strong linear dependence of log(1/IC50) on log P. Thus, the more lipophilic, the more active it was found be. The 7-CN series 45–51 showed no such dependence. The resistance index (IC50 K1/IC50 D10) also exhibited a linear dependence on log P, with a substantially steeper slope in the case of the 7-Cl series. The findings demonstrate the feasibility of producing hydrophilic analogues with strong activity and low cross-resistance with chloroquine.

New 1,3-diarylureas linked by CC Suzuki coupling to the methyl 3-aminothieno[3,2-b]pyridine-2-carboxylate moiety: Synthesis and fluorescence studies in solution and in lipid membranes

► Six new 1,3-diarylurea derivatives in the thieno[3,2- b ]pyridine series were synthesized. ► The fluorescence properties of the new compounds were studied in solution and in lipid membranes. ► The compounds were incorporated in lipid membranes of DPPC, DPPG, egg lecithin and DODAB. ► These compounds are useful to monitor changes in fluidity of lipid membranes. New six fluorescent 1,3-diarylureas linked by C C Suzuki coupling to the 6-position of the methyl 3-aminothieno[3,2- b ]pyridine-2-carboxylate moiety were prepared by reaction of the amino groups on the ortho or meta positions relative to the C C bond of the Suzuki coupling products, with different para -substituted arylisocyanates (H, OMe, CN), in high to excellent yields. The fluorescence properties of the 1,3-diarylureas in solution and in lipid membranes of egg yolk phosphatidylcholine (Egg-PC), dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylglycerol (DPPG) or dioctadecyldimethylammonium bromide (DODAB), with or without cholesterol (Ch), were studied. The six 1,3-diarylureas have reasonable fluorescence quantum yields in several solvents (0.02 ≤ Φ F ≤ 0.69) and present a moderately solvent sensitive emission, but are not fluorescent in alcohols and water. The compounds bearing the arylurea moiety in the meta position relative to the C C bond, especially with the OMe and CN substituents, present the better solvatochromic properties. Incorporation of the six compounds in lipid membranes indicates that all the compounds are deeply located in the hydrophobic region of the lipid bilayers, feeling the transition between the rigid gel phase and fluid phases.

Controlling the electron-deficiency of self-assembling pyrazine-acenes: a collaborative experimental and theoretical investigation

This paper reports novel pyrazine-acenes containing electron-deficient heteroaromatic π-extenders, such as pyridine, pyrazine, and benzothiadiazole, directly fused with pyrazine. Electronic properties of these systems were characterized by UV-Vis, fluorescence spectroscopy, and cyclic voltammetry. Computational electronic property evaluation of all experimentally synthesized compounds is provided, and is coupled with electronic calculations of closely related compounds that were not synthetically feasible. Our theoretical results provide insight into the overall analysis and interpretation of the experimentally observed trends. In this study, we found a systematic decrease in the LUMO energy (E(LUMO)) with an increasing number of imine functions in the π-extender. Additionally, when comparing the pyrazine-acene containing pyrazine π-extender to a reference compound with C≡N peripheral substituents, we found that the imine function is comparable to the C≡N substituent in lowering E(LUMO). The most dramatic E(LUMO) lowering was experimentally observed using dibromobenzothiadiazole as a π-extender. In all cases, the HOMO energy (EHOMO) was negligibly affected, thus we found options for electronic property control based solely on E(LUMO) manipulation. This is computationally validated by an examination of the molecular orbitals in which the LUMO orbital was found predominantly on the π-extender section of the molecules, while the HOMO orbital was localized away from the π-extender. Interestingly, the self-assembly of all the experimentally synthesized compounds showed excellent one-dimensional fiber formation in spite of their large π-core framework. These fibers were characterized by atomic force microscopy and UV-Vis spectroscopy.

ChemInform Abstract: Highly Efficient and Selective Reduction of Nitroarenes with Hydrazine over Supported Rhodium Nanoparticles.

AbstractA rhodium/porous ionic copolymer nanocatalyst can be used at low loading (0.1‐1.0 mol%) for the selective reduction of the nitro group of nitroarenes in the presence of halide (F, Cl, Br, I), CN, NH2, OH, amide, ester, and alkene substituents to give the corresponding anilines quantitatively.

1,1‐Dicyano‐4‐[4‐(diethylamino)phenyl]buta‐1,3‐dienes: Structure–Property Relationships

AbstractWe report the synthesis and physical study of a series of 1,1‐dicyano‐4‐[4‐(diethylamino)phenyl]buta‐1,3‐dienes in which the number and position of additional CN substituents along the 1,1‐dicyanobuta‐1,3‐dienyl fragment is systematically varied. While X‐ray analysis provided unambiguous information about molecular geometries in the crystal, UV/Vis and electrochemical measurements, by cyclic voltammetry (CV) and rotating disk voltammetry (RDV), revealed that introduction of additional cyano groups in the C2‐ and C4‐positions most affected the optical properties of these molecules in solution, in terms of intramolecular charge‐transfer absorption energy and intensity. A comparison with structurally related chromophores indicates that the shift of the anilino donor from position 2/3 to 4 along the butadiene scaffold results in a remarkable bathochromic shift of the ICT absorption maxima, mainly due to the higher planarity in the present series. These findings are further corroborated by density functional theory calculations. Preliminary nonlinear optical (NLO) measurements confirm the promise of the new push‐pull chromophores as third‐order nonlinear‐optical molecular materials.

Anion Binding by Electron-Deficient Arenes Based on Complementary Geometry and Charge Distribution.

Extended electron-deficient arenes are investigated as potential neutral receptors for polyanions. Anion binds via σ interaction with extended arenes, which are composed solely of C and N ring atoms and CN substituents. As a result, the positive charge on the aromatic C is enhanced, consequently maximizing binding strength. Selectivity is achieved because different charge distributions can be obtained for target anions of a particular geometry. The halides F(-) and Cl(-) form the most stable complex with 6, while the linear N3(-) interacts most favorably with 7. The trigonal NO3(-) and tetrahedral ClO4(-) fit the 3-fold rotational axis of 6 but do not form stable complexes with 5 and 7. The Y-shaped HCOO(-) forms complexes with 4, 5, and 7, with the latter being the most stable. Thus, the anion complexes exhibit strong binding and the best geometrical fit between guest and host, reminiscent of Lego blocks.