Nonplanar Molecules Research Articles

Luminescence switching of a persistent room-temperature phosphorescent pure organic molecule in response to external stimuli.

4-(Carbazol-9-yl)benzaldehyde could emit yellow RTP, which could last for 3 s because of efficient intersystem crossing. Moreover, multicolor luminescent switches could be realized by simply applying a mechanical force stimulus.

A “Blind Area” in Geometrical Parameters Taken from Crystal Diffraction Data

Symmetrically independent geometrical parameters of six molecules, viz. benzene C6H6 (D6h), pyridine C5H5N (C2v), diphenyl C6H5–C6H5 (D2), 2,2′-dipyridine C5H4N–C5H4N (C2), naphthalene C10H8 (D2h), ferrocene (C5H5)2Fe (D5), and substituted (η5-C5H5)FeCp′ molecular fragment, were calculated from crystal structures deposited in the Cambridge Structural Database (CSD). Average CSD interatomic distances from low-temperature (LT) studies are systematically shortened by 0.01–0.02 Å in comparison with gas electron diffraction results for free molecules; room temperature CSD bond lengths are further reduced relative to LT ones. Bicyclic diphenyl and 2,2′-dipyridine display a similar distribution of planar (mostly in special positions) and nonplanar molecules with the interring dihedral angle varying up to 49.6° and 46.0°, respectively. A strong positive correlation between C–C and Fe–C bond lengths was observed in (η5-C5H5)Fe fragments. Bond angle values at neighboring atoms in planar cycles are negatively correlated. In all cases, distributions of CSD data contain a “blind area” where data points are randomly scattered within 0.02–0.04 Å (bond distances) and 2–3° (bond angles) independent of R-factor when R < 0.06. This area broadens with increasing temperature of a study. These observations correspond well to the model of a static and/or dynamic disorder of molecules between discrete sets of atomic positions in a crystal.

Internal rotation potential and structure of six fluorine substituted nitrobenzenes studied by microwave spectroscopy supported by quantum chemical calculations

Microwave spectra of the vibrational ground state and several torsionally excited states were used to investigate the internal rotation potential and the structure of six fluorine substituted nitrobenzenes: 3-fluoro- and 4-fluoronitrobenzene were planar molecules just as nitrobenzene whereas 2-fluoro-, 2,4-difluoro- and 2,5-difluoronitrobenzene were found to be non-planar with a dihedral angle, γ0, between the benzene ring and the nitro group of 31.8°, 27.1°, and 30.0° respectively and 2,4,6-trifluoronitrobenzene was non-planar with γ0=55.0°. The lower of the two barriers separating the potential minima in the non-planar molecules were 125.5, 74.9, 98.4 and 163cm−1 respectively. Parameters for structural relaxation during the internal rotation were calculated by the B3LYP method using aug-cc-pVDZ basis and by the MP2(full) method using aug-cc-pVTZ basis. Using these relaxation parameters clearly improved the fit by the internal rotation model, SAF, to observed rotational constants as compared with fits without relaxation of structure. For 2-fluoro-, 2,4-difluoro- and 2,5-difluoronitrobenzene the coefficients V2, V4 and V6 in the Fourier expansion of the potential were determined. For the planar molecules and for 2,4,6-trifluoronitrobenzene V2 and V4 were determined using assumptions about V6 based on the quantum chemical calculations. For all non-planar molecules tunnelling through the lower of the two barriers was observed as a splitting of the torsional energy levels.

Intermediate sp-hybridization for chemical bonds in nonplanar covalent molecules of carbon

General representations for symmetrical and asymmetrical intermediate sp-hybridization are provided, with which the development of electronic structure in C3v-symmetrical C2H6 and the bonding configuration in C60 have been analyzed as an example. The spherical structure of C60 does not necessarily require the fourth hybrid, h4, to lie along the radial direction. Rather, h4 runs at an angle of 3.83° from the radius, in the plane bisecting a pentagon, to achieve maximum overlap with adjacent h4-hybrids. By virtue of these representations, a number of properties of covalent molecules and solids can be conveniently calculated. This work might be particularly helpful for the study of C—C bonding in curved structures of carbon, such as fullerenes, carbon nanotubes, and buckled graphene.

N′-[(1E)-1-(2-Fluorophenyl)ethylidene]pyridine-3-carbohydrazide

The title compound, C14H12FN3O, adopts an E conformation with respect to the azomethine double bond whereas the N and methyl C atoms are in a Z conformation with respect to the same bond. The ketonic O and azomethine N atoms are cis to each other. The non-planar mol­ecule [the dihedral angle between the benzene rings is 7.44 (11)°] exists in an amido form with a C=O bond length of 1.221 (2) Å. In the crystal, a bifurcated N—H⋯(O,N) hydrogen bond is formed between the amide H atom and the keto O and imine N atoms of an adjacent mol­ecule, leading to the formation of chains propagating along the b-axis direction. Through a 180° rotation of the fluoro­phenyl ring, the F atom is disordered over two sites with an occupancy ratio of 0.632 (4):0.368 (4).

Synthesis, Characterization, and Biological Activity of N (')-[(Z)-(3-Methyl-5-oxo-1-phenyl-1,5-dihydro-4H-pyrazol-4-ylidene)(phenyl)methyl]benzohydrazide and Its Co(II), Ni(II), and Cu(II) Complexes.

Reaction of 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one and benzoyl hydrazide in refluxing ethanol gave N ′-[(Z)-(3-methyl-5-oxo-1-phenyl-1,5-dihydro-4H-pyrazol-4-ylidene)(phenyl)methyl]benzohydrazide (HL1), which was characterized by NMR spectroscopy and single-crystal X-ray structure study. X-ray diffraction analyses of the crystals revealed a nonplanar molecule, existing in the keto-amine form, with intermolecular hydrogen bonding forming a seven-membered ring system. The reaction of HL1 with Co(II), Ni(II), and Cu(II) halides gave the corresponding complexes, which were characterized by elemental analysis, molar conductance, magnetic measurements, and infrared and electronic spectral studies. The compounds were screened for their in vitro cytotoxic activity against HL-60 human promyelocytic leukemia cells and antimicrobial activity against some bacteria and yeasts. Results showed that the compounds are potent against HL-60 cells with the IC50 value ≤5 μM, while some of the compounds were active against few studied Gram-positive bacteria.

Timescales for adiabatic photodissociation dynamics from the ${\rm \tilde A}$Ã state of ammonia

Photodissociation dynamics after excitation of the à state ν'2 = 4 (umbrella) level of ammonia are investigated using ultrafast time-resolved velocity map ion imaging (TR-VMI). These studies extend upon previous TR-VMI measurements [K. L. Wells, G. Perriam, and V. G. Stavros, J. Chem. Phys. 130, 074308 (2009)], which reported the appearance timescales for ground state NH2(X̃)+H photoproducts, born from non-adiabatic passage through an X̃/à state conical intersection (CI) at elongated H-NH2 bond distances. In particular, the present work sheds new light on the formation timescales for electronically excited NH2(Ã)+H species, generated from NH3 parent molecules that avoid the CI and dissociate adiabatically. The results reveal a step-wise dynamical picture for the production of NH2(Ã)+H products, where nascent dissociative flux can become temporarily trapped∕impeded around the upper cone of the CI on the à state potential energy surface (PES), while on course towards the adiabatic dissociation asymptote - this behavior contrasts the concerted mechanism previously observed for non-adiabatic dissociation into H-atoms associated with ro-vibrationally "cold" NH2(X̃). Initially, non-planar NH3 molecules (species which have the capacity to yield adiabatic photoproducts) are found to evolve out of the vertical Franck-Condon excitation region and towards the CI region of the à state PES with a time-constant of 113 ± 46 fs. Subsequently, transient population encircling the CI then progresses to finally form NH2(Ã)+H photoproducts from the CI region of the à state PES with a slower time-constant of 415 ± 25 fs. Non-adiabatic dissociation into ro-vibrationally "hot" NH2(X̃) radicals together with H-atoms is also evidenced to occur via a qualitatively similar process.

Orientation of molecular interface dipole on metal surface investigated by noncontact atomic force microscopy

We investigated the orientations of interface dipole moments of individual non-planar titanyl phthalocyanine (TiOPc) molecules on Cu(111) and Cu(100) substrates using scanning tunneling microscope (STM) and noncontact atomic force microscope (NC-AFM). The dipole moment orientations corresponding to two different configurations of individual TiOPc molecules were determined unambiguously. The correlation between the actual molecular structures and the corresponding STM topographies is proposed based on the sub-molecular resolution imaging and local contact potential difference (LCPD) measurements. Comparing with the pristine substrate, the LCPD shift due to the adsorption of non-planar molecule is dependent on the permanent molecular dipole, the charge transfer between the surface and the molecule, and the molecular configurations. This work would shed light on tailoring interfacial electronic properties and controlling local physical properties via polar molecule adsorption.

Synthesis of novel thieno-[3,4-b]-pyrazine-cored molecules as red fluorescent materials

Two novel thieno-[3,4-b]-pyrazine-based molecules, TP-E and TP-O, were designed and synthesized for potential application as red fluorescent emitters. The bulky tetraphenylethylene groups were attached at the periphery of the thieno-[3,4-b]-pyrazine core to form the non-planar molecules, as efficient solid-state emitting materials. The peripheral groups were grafted to the emissive core through either a conjugated acetylene bond, or a non-conjugated ether bond. These molecules exhibit strong red fluorescence in both dilute solutions and in thin films with large Stokes shifts of over 100 nm. The cyclic voltammetry measurements showed the reversible oxidation and reduction behavior for both compounds. All these properties indicate the two compounds are possible functional materials for use in optoelectronic devices.

Resonance Raman Detection and Estimation in the Aqueous Phase Using Water Dispersible Cyclodextrin: Reduced-Graphene Oxide Sheets

Resonance Raman spectroscopy is a powerful analytical tool for detecting and identifying analytes, but the associated strong fluorescence background severely limits the use of the technique. Here, we show that by attaching β-cyclodextrin (β-CD) cavities to reduced graphene-oxide (rGO) sheets we obtain a water dispersible material (β-CD: rGO) that combines the hydrophobicity associated with rGO with that of the cyclodextrin cavities and provides a versatile platform for resonance Raman detection. Planar aromatic and dye molecules that adsorb on the rGO domains and nonplanar molecules included within the tethered β-CD cavities have their fluorescence effectively quenched. We show that it is possible using the water dispersible β-CD: rGO sheets to record the resonance Raman spectra of adsorbed and included organic chromophores directly in aqueous media without having to extract or deposit on a substrate. This is significant, as it allows us to identify and estimate organic analytes present in water by resonance Raman spectroscopy.

Anti-recombination organic dyes containing dendritic triphenylamine moieties for high open-circuit voltage of DSSCs

Three novel sensitizers with dendritic triphenylamine moieties were synthesized and used for dye-sensitized solar cells (DSSCs). Their absorption spectra, electrochemical and photovoltaic properties were extensively investigated. All three DSSCs exhibit high open-circuit voltage over 0.8 V. The photovoltaic results indicate that the dendritic triphenylamine units improve the open-circuit voltage, which is attributed to the retardation of charge recombination, demonstrating that non-planar and larger molecules exert better blocking function. Under standard global AM 1.5 solar conditions, the best performance of the DSSCs exhibits a short-circuit current density of 10.35 mA cm−2, an open-circuit voltage of 0.836 V and a fill factor of 0.68, corresponding to an overall conversion efficiency of 5.87%.

Charge mobility in molecules: Charge fluxes from second derivatives of the molecular dipole

On the basis of the analytical model previously suggested by Dinur, we discuss here a method for the calculation of vibrational charge fluxes in planar molecules, obtained as numerical second derivatives of the molecular dipole moment. This model is consistent with the partitioning of the atomic polar tensors into atomic charge and charge fluxes according to the Equilibrium Charges-Charge Fluxes model and it is directly related to experimentally measurable quantities such as IR intensities. On the basis of density functional theory calculations carried out for several small benchmark molecules, the complete set of charge fluxes is calculated for each molecule and compared with the approximated flux parameters previously derived and reported in the past literature. The degree of localization of charge fluxes is investigated and discussed; in addition, some approximations are analyzed in order to verify the applicability of the method to large and∕or non-planar molecules, aimed at obtaining a description of the electron charge mobility in different molecular environments.

A second monoclinic polymorph of 2-(3,5-dimethyl-1H-pyrazol-1-yl)-2-hydroxyimino-N′-[1-(pyridin-2-yl)ethylidene]acetohydrazide

The title compound, C14H16N6O2, is a second monoclinic polymorph of 2-[1-(3,5-dimeth­yl)pyrazol­yl]-2-hy­droxy­imino-N′-[1-(2-pyrid­yl)ethyl­idene] acetohydrazide, with two crystallographically independent mol­ecules per asymmetric unit. The non-planar mol­ecules are chemically equal having similar geometric parameters. The previously reported polymorph [Plutenko et al. (2012 ▶). Acta Cryst. E68, o3281] was described in space group Cc (Z = 4). The oxime group and the O atom of the amide group are anti with respect to the C—C bond. In the crystal, mol­ecules are connected by N—H⋯N hydrogen bonds into zigzag chains extending along the b axis.

Photoelectron diffraction in the x-ray and ultraviolet regime: Sn-phthalocyanine on Ag(111)

The bonding geometry of tin-phthalocyanine (SnPc) on Ag(111) has been studied using x-ray and ultraviolet photoelectron diffraction (XPD and UPD, respectively). Experimental diffraction patterns were compared to single-scattering-cluster calculations. XPD data could be well reproduced by the simulations and allowed for the determination of several structural parameters. At a coverage of 0.9 ML, all molecules are in a ``tin-down'' configuration and the nonplanar shuttlecock-shaped SnPc molecule undergoes flattening upon absorption on Ag(111). UPD data from the second highest occupied molecular orbital and comparison to simulations show a high sensitivity to minor structural changes, including also the vertical distance between tin atoms of the SnPc and the surface layer of the substrate, which is found to be 2.3 \AA{}. We thus demonstrate how UPD can complement the well-established XPD method and discuss remaining challenges in the theoretical description of photoelectron diffraction from molecular orbitals at low energies. The UPD method is particularly attractive in view of the increasing availability of ultrashort pulsed laser sources in the XUV regime, which could enable pump-probe experiments with high structural sensitivity.

A bulky pyridinylfluorene-fuctionalizing approach to synthesize diarylfluorene-based bipolar host materials for efficient red, green, blue and white electrophosphorescent devices

By incorporating electron-transporting pyridine and hole-transporting fluorene moieties into a nonplanar 3-dimensional molecule, via the sp3-hybridized carbon linkage by Friedel–Crafts reaction, three novel donor–acceptor (p–n) bipolar host materials 9-(pyridin-2-yl)-3-(9-(pyridin-2-yl)-fluoren-9-yl)-carbazole (CzPy-PyFM), 3,6-bis(9-(pyridine-2-yl)-fluoren-9-yl)-9-(pyridin-2-yl)-carbazole (CzPy-DPyFM) and 5,5′′-bis(9-(pyridin-2-yl)-fluoren-9-yl-)-2,2′:5′,2′′-terthiophene (T3DPyFM) have been synthesized successfully. These pyridinylfluorene end-capped materials with large steric hindrance have been applied as efficient universal hosts for blue, green and red PhOLEDs. The blue, green, and red PhOLEDs hosted by highly thermally stable CzPy-PyFM exhibit the maximum external quantum efficiencies (EQEs) of 10.49%, 11.04%, and 6.50%, respectively. On this basis, the single-emissive-layer three-color and all-phosphor CzPy-PyFM-based white PhOLEDs have been fabricated, which acquire a maximum current efficiency of 10.4 cd A−1, a power efficiency of 10.2 lm W−1 and an EQE of 5.58%. This is the first example of the diarylfluorenes as universal hosts for full-color RGB PhOLEDs as well as white PhOLEDs.

Recent Advances in Transition Metal Catalyzed Decarboxylative Coupling Reactions of Alkyl Carboxylic Acid

Carboxylic acids are cheap, readily available, easy to store and handle compounds. Since the studies of decarboxylative Heck reaction of aryl carboxylic acids, transition metal-catalyzed decarboxylative coupling reactions have become an interesting research area. Transition metal-catalyzed alkyl coupling plays an important role in the synthesis of nonplanar molecule. Thus, much attention has been paid to the development of transition metal-catalyzed decarboxylative cross-coupling reactions of alkyl carboxylic acids. This review focuses on: (1) the copper-catalyzed decarboxylative coupling reaction between proline derivatives and nucleophilies including terminal alkynes (Csp3—Csp), indoles (Csp3—Csp2) and nitromethane (Csp3—Csp2), the copper-catalyzed decarboxylative aldol reaction of thioester derivatives, the copper-catalyzed decarboxylative Mannich-type reaction; the copper-catalyzed decarboxylative alkynylation of quaternary α-cyano acetate salts; (2) the palladium-caytalyzed decarboxylative couplings of 2-(2-azaaryl)acetates, cyanoacetate, salts, nitrophenyl acetates salts with aryl halides; (3) the silver-catalyzed decarboxylative chlorination, fluorination and alkynylation.

Self-assembly of dendronized non-planar conjugated molecules on a HOPG surface

Two-dimensional self-assembly of a series of dendronized molecules with different functional groups were observed on the highly oriented pyrolitic graphite (HOPG) surface by scanning tunneling microscopy (STM). The solution evaporation of these molecules on HOPG surfaces under ambient conditions results in the formation of self-organized monolayers. STM images demonstrate that the dendronized conjugated moiety in these molecules all adopt an edge-on arrangement on the HOPG surface, revealing the importance of π–π stacking interactions. The molecules with a hydroxyl as the substituent group adsorb on the HOPG surface with an ordered lamellar nanopattern resulting from the intermolecular hydrogen bonding. The molecules without alkyl chain are perpendicular to the HOPG surface, in a face-to-face card-stack fashion by π–π stacking. Alkyl chain assisted molecules adsorb on the HOPG surface with one side chain arrangement by tail-to-tail fashion. Our results demonstrate that the balance between different molecule–molecule and molecule–substrate interactions can be easily influenced by a small structural change in one of the components of the supramolecular assemblies resulting in different organized patterns on the solid surface.

Molecular Encapsulation in Pyrogallolarene Hexamers Under Nonequilibrium Conditions

Pyrogallol[4]arene is a macrocycle with a concave surface and 12 peripheral hydroxyl groups that mediate its self-assembly to form hexamers of octahedral symmetry in the solid state, in solution, and in the gas phase. These hexamers enclose approximately 1300 Å(3) of space, which is filled with small molecules. In this study, we show that solvent-free conditions for guest entrapment in these hexamers, using molten guest molecules as solvent and allowing the capsules to assemble during cooling, results in exceptionally kinetically stable encapsulation complexes that are not formed in the presence of solvent and are not thermodynamically stable. The capsules' kinetic stabilities are strongly dependent on the size and shape of both guest and solvent molecules, with larger or nonplanar molecules with rigid geometries providing enhanced stability. The greatest observed barrier to guest exchange, ΔG(‡) = 32 ± 0.7 kcal mol(-1) for encapsulated CCl(4) → encapsulated pyrene, is, to the best of our knowledge, indicative of the most powerful kinetic trap ever observed for a synthetic, hydrogen-bonded encapsulation complex. Detailed NMR studies of the structures of the assemblies and the kinetics and mechanisms for guest exchange reveal that subtle differences in guest and solvent structure can impart profound effects on the behavior of the systems. Kinetic and thermodynamic stability, capsule symmetry and structure, guest tumbling rates, susceptibility to disruption by polar solvents, and even the mechanism for equilibration-the presence or absence of supramolecular intermediates-are all greatly influenced. The strongest observed kinetic traps provide encapsulation complexes that are not at equilibrium but are nonetheless indefinitely persistent at ambient temperatures, a property that invites future applications of supramolecular chemistry in open systems where equilibrium is not possible.

Quantum Switching of π-Electron Rotations in a Nonplanar Chiral Molecule by Using Linearly Polarized UV Laser Pulses

Nonplanar chiral aromatic molecules are candidates for use as building blocks of multidimensional switching devices because the π electrons can generate ring currents with a variety of directions. We employed (P)-2,2'-biphenol because four patterns of π-electron rotations along the two phenol rings are possible and theoretically determine how quantum switching of the π-electron rotations can be realized. We found that each rotational pattern can be driven by a coherent excitation of two electronic states under two conditions: one is the symmetry of the electronic states and the other is their relative phase. On the basis of the results of quantum dynamics simulations, we propose a quantum control method for sequential switching among the four rotational patterns that can be performed by using ultrashort overlapped pump and dump pulses with properly selected relative phases and photon polarization directions. The results serve as a theoretical basis for the design of confined ultrafast switching of ring currents of nonplanar molecules and further current-induced magnetic fluxes of more sophisticated systems.

Covalently Linked, Water-Dispersible, Cyclodextrin: Reduced-Graphene Oxide Sheets

Reduced-graphene oxide (rGO) sheets have been functionalized by covalently linking β-cyclodextrin (β-CD) cavities to the sheets via an amide linkage. The functionalized β-CD:rGO sheets, in contrast to rGO, are dispersible over a wide range of pH values (2-13). Zeta potential measurements indicate that there is more than one factor responsible for the dispersibility. We show here that planar aromatic molecules adsorbed on the rGO sheet as well as nonplanar molecules included in the tethered β-CD cavities have their fluorescence effectively quenched by the β-CD:rGO sheets. The β-CD:rGO sheets combine the hydrophobicity associated with rGO along with the hydrophobicity of the cyclodextrin cavities in a single water-dispersible material.