Synthesis of Hydroxyalkyl‐Substituted,Push–Pull Chromophores based on Diphenylacetylenes and 1,4‐Bis(phenylethynyl)benzenes

Six new push–pull chromophores based on phenylacetylenes were prepared: two 1,2‐diphenylacetylenes and four 1,4‐bis(phenylethynyl)benzenes. The donor amino groups have hydroxyethyl substituents, and the acceptor groups are cyano or nitro. More soluble versions were made by including two methoxy groups on the central phenyl ring.     

Towards Solar Energy Storage in the Photochromic Dihydroazulene–Vinylheptafulvene System

One key challenge in the field of exploitation of solar energy is to store the energy and make it available on demand. One possibility is to use photochromic molecules that undergo light‐induced isomerization to metastable isomers. Here we present efforts to develop solar thermal energy storage systems based on the dihydroazulene (DHA)/vinylheptafulvene (VHF) photo/thermoswitch. New DHA derivatives with one electron‐withdrawing cyano group at position 1 and one or two phenyl substituents in the five‐membered ring were prepared by using different synthetic routes. In particular, a diastereoselective reductive removal of one cyano group from DHAs incorporating two cyano groups at position 1 turned out to be most effective. Quantum chemical calculations reveal that the structural modifications provide two benefits relative to DHAs with two cyano groups at position 1: 1) The DHA–VHF energy difference is increased (i.e., higher energy capacity of metastable VHF isomer); 2) the Gibbs free energy of activation is increased for the energy‐releasing VHF to DHA back‐reaction. In fact, experimentally, these new derivatives were so reluctant to undergo the back‐reaction at room temperature that they practically behaved as DHA to VHF one‐way switches. Although lifetimes of years are at first attractive, which offers the ultimate control of energy release, for a real device it must of course be possible to trigger the back‐reaction, which calls for further iterations in the future.     

Intrinsic conformational characteristics of alpha,alpha-diphenylglycine

Quantum mechanical calculations at the B3LYP/6-31+G(d,p) level have been used to investigate the intrinsic conformational preferences of alpha,alpha-diphenylglycine, a simple alpha,alpha-dialkylated amino acid bearing two phenyl substituents on the alpha-carbon, in both the gas phase and aqueous solution. Nine minimum energy conformations have been characterized for the N-acetyl-N'-methylamide derivative within a relative energy range of about 9 kcal/mol. The relative stability of these structures is largely influenced by specific backbone...side chain and side chain...side chain interactions that can be attractive (N-H...pi and C-H...pi) or repulsive (C=O...pi). On the other hand, comparison with the minimum energy conformations calculated for alpha-aminoisobutyric acid, in which the two phenyl substituents are replaced by methyl groups, revealed that the bulky aromatic rings of alpha,alpha-diphenylglycine induce strain in the internal geometry of the peptide. Finally, a set of force-field parameters for classical Molecular Mechanics calculations was developed for the investigated amino acid. Molecular Dynamics simulations in aqueous solutions have been carried out to validate the parameters obtained.     

Intrinsic conformational preferences of C(alpha,alpha)-dibenzylglycine

The intrinsic conformational preferences of C (alpha,alpha)-dibenzylglycine, a symmetric alpha,alpha-dialkylated amino acid bearing two benzyl substituents on the alpha-carbon atom, have been determined using quantum chemical calculations at the B3LYP/6-31+G(d,p) level. A total of 46 minimum energy conformations were found for the N-acetyl- N'-methylamide derivative, even though only nine of them showed a relative energy lower than 5.0 kcal/mol. The latter involves C 7, C 5, and alpha' backbone conformations stabilized by intramolecular hydrogen bonds and/or N-H...pi interactions. Calculation of the conformational free energies in different environments (gas-phase, carbon tetrachloride, chloroform, methanol, and water solutions) indicates that four different minima (two C 5 and two C 7) are energetically accessible at room temperature in the gas phase, while in methanol and aqueous solutions one such minimum (C 5) becomes the only significant conformation. Comparison with results recently reported for C (alpha,alpha)-diphenylglycine indicates that substitution of phenyl side groups by benzyl enhances the conformational flexibility leading to (i) a reduction of the strain of the peptide backbone and (ii) alleviating the repulsive interactions between the pi electron density of the phenyl groups and the lone pairs of the carbonyl oxygen atoms.     

1,3‐Dimethyl‐2‐oxo‐4,6‐diphenyl‐1,2,3,4‐tetrahydropyridine‐3‐carbonitrile

The crystal structure of the title compound, C₂₀H₁₈N₂O, reveals a distorted half‐chair conformation of the central tetra­hydro­pyridine (THP) ring, with the cyano‐ and adjacent phenyl‐substituted C atoms displaced by 0.329 (1) and ?0.315 (1) Å, respectively, from the THP best plane. Steric interactions force the phenyl rings out of the THP plane by 49.21 (9) and 65.76 (5)°. The cyano moiety is coplanar with the THP plane.     

1,3‐Bis(4‐nitro­phenyl)­triazene

The structure of the title compound, C₁₂H₉N₅O₄, reveals an almost planar mol­ecule (r.m.s. deviation = 0.061 Å), in which the interplanar angle between the phenyl rings is 5.7 (1)° and the largest interplanar angle is that between the phenyl ring and the nitro group of one of the 4‐nitro­phenyl substituents [8.8 (3)°]. The observed mol­ecular conformation suggests a delocalization of π‐electrons extended over the diazo­amine group and the terminal aryl substituents. Intermolecular N—H⃛O interactions between the twofold screw‐related mol­ecules give rise to helical chains along the [010] direction. Intermolecular C—H⃛O interactions then generate sheets of mol­ecules in the (10) plane, and these sheets are held together by N⃛C and O⃛O π–π interactions.     

Click Chemistry Derived Pyridazines: Electron‐Deficient Building Blocks with Defined Conformation and Packing Structure

A series of 3,6‐bis(4‐triazolyl)pyridazines equipped with terminal phenyl substituents with varying degree of fluorination were synthesized by using the facile copper‐catalyzed azide–alkyne cycloaddition and their structures were thoroughly investigated in the gas phase, in solution, and in the solid state by employing DFT calculations, NMR spectroscopy, and single‐crystal X‐ray diffraction, respectively. On the molecular level, their structure is governed by the strong preference of the triazole‐pyridazine linkages for the anti ‐conformation. The supramolecular organization of the molecules in the crystalline solid is controlled by π‐stacking, C−H⋅⋅⋅π as well as C−F⋅⋅⋅H interactions. The latter can conveniently be tuned by the number and position of fluorine substituents in the terminal phenyl units, giving rise to either herringbone‐like, 1D or 2D lamellar packing. Electrochemistry and optical spectroscopy of all compounds suggest that they might find use as electron‐transporting/hole‐blocking materials in organic electronics.     

Synthesis and characterization of a novel ambipolar polymer semiconductor based on a fumaronitrile core as an electron‐withdrawing group

Two conjugated polymers containing stilbene and fumaronitrile moieties were synthesized to investigate their electronic properties by the existence of electron‐withdrawing cyano groups on a vinylene backbone. The cyclic voltammetry investigation and time‐dependent density functional theory calculations indicated that the cyano substituents lowered the lowest unoccupied molecular orbital (LUMO) energy level by about 0.65 and 0.63 eV, respectively. The lowering of the LUMO energy levels due to the electron‐withdrawing properties of the cyano substituents could enhance electron injection capability. Furthermore, bithiophene‐fumaronitrile (donor‐acceptor) intermolecular interaction facilitates the self‐assembly of the polymer chains. Organic field‐effect transistors (OFETs) based on PBTSB without the electron‐withdrawing group only exhibit hole transport, while OFETs based on PBTFN with cyano substituents exhibit ambipolar characteristics. The growth of PBTFN crystalline fibrils was observed with increasing annealing temperature, which enhanced hole and electron mobility. A complementary‐like inverter using PBTFN with ambipolar properties exhibited good symmetry with an inverting voltage nearly half that of the power supply with a gain of 9 at V_DD = 100 V. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Toward pi-conjugated molecule bundles: synthesis of a series of B,B',B''-trianthryl-N,N',N''-triarylborazines and the bundle effects on their properties

As a prototype of a pi-conjugated molecule bundled system, a series of B,B',B'-trianthryl- N,N',N'-triarylborazine derivatives bearing various p-substituted phenyl groups (p-R-C(6)H(4): R = hexyl (1), i-Pr (2), CF(3) (3), Br (5)) as aryl groups was designed and synthesized. The crystal structure analysis of these derivatives confirmed that the three anthryl and three phenyl groups are bundled up alternately in a C(3) symmetrical gear-shaped fashion. On the basis of this structure, the trianthrylborazine derivatives form a unique honeycomblike packing structure consisting of intermolecular pi-stacking of the anthryl moieties. Significant bundle effects were observed in the photophysical and electrochemical properties of these compounds. In their fluorescence spectra, the trianthrylborazine derivatives (1-3) show intense emissions around 390 nm, whose quantum yields (1, Phi(F) = 0.62; 2, Phi(F) = 0.59; 3, Phi(F) = 0.63) are about twice high as that of anthracene (Phi(F) = 0.27). The cyclic voltammetry measurements show that the oxidation peak potential can be tuned by varying the substituents on the phenyl moieties. Theoretical calculations (B3LYP/ 6-31G(d)) suggested that secondary through-bond/through-space interactions in the bundled structure play an important role in the tuning of these properties. Facile structural derivatization at the 10-position of the anthryl moieties of trianthrylborazine was conducted to demonstrate the utility of the borazine skeleton as a core framework for new organic electronic materials.     

The crystal and molecular structure of the 2,4,6,8 tetra-t-Bu-phenothiazine 0.5 benzene adduct

The crystal structure of 2,4,6,8-tetra-t-Bu-phenothiazine 0.5C₆H₆ (Pnma space group, a=11.685, b=25.593, c=10.339) shows short intermolecular t-Bu(CH₃)Ph and CH₃CH₃ contacts which allow the formation of well defined channels along the a direction. These channels host one benzene molecule for each pair of phenothiazine molecules. AM1 molecular orbital calculations suggest that there is a strong coupling of the t-Bu groups rotations and the folding of the ring and this in turn makes the phenothiazine skeleton to be less folded than expected from the presence of four electron donating substituents.     

Synthesis,characterization, and in vitro biological studies of some novel pyran fused pyrimidone derivatives

A variety of pyrano[2,3‐d]pyrimidine‐5‐one derivatives 5 , 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j , 6 , 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j have been synthesized from 6‐amino‐4‐(substituted phenyl)‐5‐cyano‐3‐methyl‐1‐phenyl‐1,4‐dihydropyrano[2,3‐c]pyrazole derivatives 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j via cyclization using formic acid and acetic acid. All the newly synthesized compounds have been characterized by IR, ¹H NMR, ¹³C NMR, and elemental analysis. All the synthesized compounds have been screened for antibacterial, antifungal and antitubercular activity. J. Heterocyclic Chem., (2012).     

Crystal structures of four δ‐keto esters and a Cambridge Structural Database analysis of cyano–halogen interactions

The revived interest in halogen bonding as a tool in pharmaceutical cocrystals and drug design has indicated that cyano–halogen interactions could play an important role. The crystal structures of four closely related δ‐keto esters, which differ only in the substitution at a single C atom (by H, OMe, Cl and Br), are compared, namely ethyl 2‐cyano‐5‐oxo‐5‐phenyl‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₂N₂O₃, (1), ethyl 2‐cyano‐5‐(4‐methoxyphenyl)‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₂₀H₂₄N₂O₄, (2), ethyl 5‐(4‐chlorophenyl)‐2‐cyano‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₁ClN₂O₃, (3), and the previously published ethyl 5‐(4‐bromophenyl)‐2‐cyano‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₁BrN₂O₃, (4) [Maurya, Vasudev & Gupta (2013). RSC Adv. 3 , 12955–12962]. The molecular conformations are very similar, while there are differences in the molecular assemblies. Intermolecular C—H...O hydrogen bonds are found to be the primary interactions in the crystal packing and are present in all four structures. The halogenated derivatives have additional aromatic–aromatic interactions and cyano–halogen interactions, further stabilizing the molecular packing. A database analysis of cyano–halogen interactions using the Cambridge Structural Database [CSD; Groom & Allen (2014). Angew. Chem. Int. Ed. 53 , 662–671] revealed that about 13% of the organic molecular crystals containing both cyano and halogen groups have cyano–halogen interactions in their packing. Three geometric parameters for the C—X...N[triple‐bond]C interaction (X = F, Cl, Br or I), viz. the N...X distance and the C—X...N and C—N...X angles, were analysed. The results indicate that all the short cyano–halogen contacts in the CSD can be classified as halogen bonds, which are directional noncovalent interactions.     

Functionalization, self-assembly, and photoswitching quenching for azobenzene derivatives adsorbed on Au(111)

We have used scanning tunneling microscopy to investigate the structure and photoswitching behavior of azobenzene molecules functionalized with bulky spacer groups and adsorbed onto Au(111). We find that positioning tert-butyl "legs" in a canted arrangement on the azobenzene phenyl rings quenches photoisomerizability of the molecule on Au(111). Addition of cyano groups at the para positions changes the molecular self-assembly significantly, but does not alter the quenched photoisomerizability. This behavior likely arises from a combination of molecule-surface interactions, molecule-molecule interactions, and alteration of azobenzene electronic structure resulting from the position-specific addition of tert-butyl groups.     

Tetraaryl Tetradecahydroporphyrazins: Novel Porphyrin Derivatives Featuring a Cyclic Benzene‐Ring Tetramer

Treatment of tetramethylsuccinonitrile 1 with aryl lithium compounds and subsequent quenching with chlorotrimethylsilane yields 5‐aryl‐3,3,4,4‐tetramethyl‐N‐(trimethylsilyl)‐3,4‐dihydropyrrol‐2‐imines 2 a – c in 49–71 % yield. Attempts to crystallise 2 a – c in the presence of wet air yielded the tetraaryl tetradecahydroporphyrazins 3 a – c in yields of 4–84 % as single diastereomers. X‐ray diffraction studies of 3 b and c showed that only the isomer with four aryl substituents pointing in the same direction was formed. The resulting four‐bladed pinwheel‐like structures were characterised by four intramolecular aromatic interactions, in which each phenyl ring points with its edge towards the centre of a neighbouring phenyl moiety, resembling the arrangement of benzene molecules in T‐shaped dimers. Temperature‐dependent NMR spectra give insight into the dynamic properties of the aryl substituents. Quantum chemical calculations that included dispersion corrections indicated the importance of aryl–aryl interactions for the diastereoselectivity of the reaction and for the structural properties of the single isomers observed.     

Long‐range heteronuclear coupling constants in 2,6‐disubstituted purine derivatives

Four‐ and five‐bond heteronuclear J‐couplings between the hydrogen H‐8 and carbons C‐6 and C‐2 in a series of 7‐ and 9‐benzyl substituted purine derivaties with variuous substituents in positions 2 and 6 were studied by coupled ¹³ C NMR and H,C‐HMBC experiments and by DFT calculations. We have found that for some of the derivatives, the five‐bond coupling H8‐C2 is higher than the four‐bond H8‐C6 coupling, which is also evidenced by a stronger crosspeak in the HMBC. This finding contradicts the generally accepted opinion that only strong three‐bond crosspeaks and one weak four‐bond H8‐C6 crosspeak can be observed in the HMBC spectra of purine derivatives. The misinterpretation of HMBC spectra may lead to an incorrect determination of the purine derivatives' structure. Copyright © 2012 John Wiley & Sons, Ltd.     

Design,synthesis, in silico analysis with PPAR‐γ receptor and study of non‐covalent interactions in unsymmetrical heterocyclic/phenyl fleximer

This work deals with the design, synthesis, in silico analysis, crystallization, and the interpretation 2‐cyano‐3‐{4‐[2‐(phthalimid‐nyl)‐propoxy]‐phenyl}‐acrylic acid ethyl ester (7). Analog 7 is designed based on rosiglitazone. The quantitative analysis of Compound 7 has been performed through single‐crystal X‐Ray Diffraction (XRD) and Hirshfeld surface analysis. Fleximer 7 has studied the role of flexibility in non‐covalent interactions and binding affinity with PPAR‐γ receptors. Both phthalimide ring and phenyl rings are linked with propylene linker. 2‐cyano‐3‐{4‐[2‐(phthalimid‐nyl)‐propoxy]‐phenyl}‐acrylic acid ethyl ester has Z = 8 in the crystal packing and stabilized by intermolecular non‐covalent interactions like C? H…O, C? H…N, C? H…л, and л…л, and so forth.     

Substituent Effects on Site Selectivity (C=C vs C=N) in Heterocumulene-Heterodiene [4 + 2] Cycloadditions: Density Functional and Semiempirical AM1 Molecular Orbital Calculations

The effect of substituents on the site selectivity (C=C vs C=N) in the [4 + 2] cycloaddition between heterocumulenes (ketene imines) 2a-g with heterodienes (acroleines 9a-n and 4-acylfuran-2,3-diones 1a-d) is treated by semiempirical AM1 molecular orbital and density functional calculations using Becke's three-parameter hybrid method (B3LYP/6-31G). For some reactions calculations were also done at the B3LYP/6-31+G level of theory. For reaction of the oxa 1,3-dienes with ketene imines unsubstituted at the terminal carbon invariably addition across the C=C heterocumulene double bond has a lower activation energy than addition across the C=N double bond. Substitution of methyl or especially phenyl groups at the ketene imine C-terminus leads to a reversal of the respective activation energies. Incorporation of the oxa 1,3-diene system into the heterocyclic dione 1 substantially enhances the reactivity ( approximately 10 kcal mol(-1) lower activation energies) as compared to similarly substituted acroleins. At the DFT level of theory all reactions are found to proceed via a concerted asynchronous mechanism.     

[4‐(Tri­fluoro­methyl)­phenyl]­aceto­nitrile

The crystal structure of the title compound, C₉H₆F₃N, at 123 K contains mol­ecules linked together via several C—H?F and C—H?N contacts, the strongest of which are 2.58 and 2.65 Å, respectively. Apparently, an F atom in the CF₃ group is able to compete with a cyano N atom for aromatic H atoms but is less prone to interact with the more acidic methyl­ene H atoms. The Ph–CH₂CN torsion angle is ?6.4 (2)° and the planar phenyl ring exhibits a typical deformation of the endo angles at the ipso‐C atoms, due to the difference in the electron‐withdrawing power of the CF₃ and CH₂CN substituents.     

Ab initio study of the substituent effects on the relative stability of the E and Z conformers of phenyl esters. Stereoelectronic effects on the reactivity of the carbonyl group

Equilibria between the Z (tau1= 0 degrees) and E (tau1= 180 degrees) conformers of p-substituted phenyl acetates 4 and trifluoroacetates 5 (X = OMe, Me, H, Cl, CN, NO2) were studied by ab initio calculations at the HF/6-31G* and MP2/6-31G* levels of theory. The preference for the Z conformer, DeltaE(HF), was calculated to be 5.36 kcal mol(-1) and 7.50 kcal mol(-1) for phenyl acetate and phenyl trifluoroacetate (i.e., with X = H), respectively. The increasing electron-withdrawing ability of the phenyl substituent X increases the preference of the Z conformer. An excellent correlation with a negative slope was observed for both series between DeltaE of the E-Z equilibrium and the Hammett sigma constant. By using an appropriate isodesmic reaction, it was shown that electron-withdrawing substituents decrease the stability of both conformers, but the effect is higher with the E conformer. Electron-withdrawing phenyl substituents decrease the delocalization of the lone pair of the ether oxygen to the C=O antibonding orbital (nO--> pi*C=O) in both the E and Z forms and in both series studied; this effect is higher in the E conformer than in the Z conformer. The nO --> pi*C=O electron donation has a minimum value with tau1= 90 degrees and a maximum value with tau1= 0 degrees (the Z conformer), the value with tau1= 180 degrees (the E conformer) being between these two values, obviously due to steric hindrance. The effects of the phenyl substituents on the reactivity of the esters studied are discussed in terms of molecular orbital interactions. ED/EW substituents adjust the availability of the pi*C=O antibonding orbital to interact with the lone pair orbital of the attacking nucleophile and therefore affect the reactivity: EW substituents increase and ED substituents decrease it. Excellent correlations were observed between the rate coefficients of nucleophilic acyl substitutions and pi*C=O occupancies of the ester series 4 and 5.     

Studies of some monocyclic and bicyclic arylacetonitriles

The high-resolution (1)H, (13)C, (1)H-(1)H COSY and (1)H-(13)C COSY NMR spectra have been recorded in CDCl(3) for arylacetonitriles 1-12 and analyzed. The arylacetonitriles 3-7 exist in two isomeric forms E (methyl group is anti to cyano group) and Z (the methyl group is syn to cyano group) in solution. Normal chair conformation with equatorial orientations of phenyl rings at C-2 and C-6 for monocyclic nitriles 1 and 2, epimeric chair structure EC (axial configuration of methyl group at C-3) for both the E and Z isomers of arylacetonitrile derivatives (3-7) and a distorted boat form, B(3), for the N-acylacetonitrile derivatives (8-10) have been proposed based on NMR data. The bicyclic nitriles 11 and 12 exist in twin chair conformations in solution. DFT calculations and chemical shifts also support these conformations. Geometry optimizations for 1-12 were carried out according to density functional theory using B3LYP/6-31G(d,p) basis set and for 1 and 8 the theoretical geometrical parameters have been compared with those of single crystal measurements.