Inter-ring Angle Research Articles

Polypyrrole/Helical Carbon Nanotube Composite with Marvelous Photothermoelectric Performance for Longevous and Intelligent Internet of Things Application.

Helical carbon nanotube (HCNT) is a vital member of carbon nanomaterials, but little effort was devoted to explore its unique characteristics and applications during the past few decades. Here, we report an organic thermoelectric composite with an excellent photothermoelectric (PTE) effect by conformally wrapping polypyrrole (PPy) on the intricate surface of HCNTs, which have been confirmed to have remarkable near-infrared (NIR) photothermal conversion capability and ultralow heat transportation characteristics. The results indicate that with the increasing HCNT content, PPy shell thickness reduces and exhibits denser as well as partial orientation, while the inter-ring angle slowly decreases and the bipolaron becomes dominant in carrier composition gradually. Consequently, the Seebeck coefficient increases monotonically, whereas the electrical conductivity remains nearly invariant. The final composite combines the benign thermoelectric properties, excellent photothermal response performance, and the lowest thermal conductivity of the carbon-based thermoelectric composite yet reported (0.064 W m-1 K-1). A single strip NIR light-stimulated adjustable delay switch was designed and fabricated, with the open-circuit voltage and short-circuit current under a 400 mW cm-2 NIR-stimulated approach to 720 μV and 62 nA with the discrepancy of consecutive periodic output signals less than 4.2%, exhibiting incredible stability and reliability and demonstrating the highest output voltage of a single strip among the reported organic PTE composite at room temperature. Our work fills in a gap of HCNT research, which hitherto existed in the PTE and thermoelectric field.

Diphosphametacyclophanes: Structural and Electronic Influences of Substituent Variation within a Family of Bis(diketophosphanyl) Macrocycles.

The condensation of MeP(SiMe3)2 with a series of 5-substituted isophthaloyl chlorides (5-R'C6H3-2,6-{C(O)Cl}2) affords the diphosphametacyclophanes m-{-C(O)-C6H3-5-R'-(C(O)PMe)}2 (R' = I, Me, tBu, Ph, and p-NCC6H4); the analogues m-{-C(O)-C5H3N-(C(O)PMe)}2 and m-{-C(O)-C6H4-(C(O)PPh)}2 are similarly obtained in preference to higher oligomers, in contrast to precedent reports. The cyclophanes all adopt butterfly-like conformations in the solid state with the P-organyl substituents adopting mutually exo arrangements. Structural and computational data suggest the nature of the 5-R substituent is key in directing the inter-ring angle and the extent of LUMO stabilization about the diketophophanyl scaffold. The latter is substantiated by UV/vis spectroscopy and cyclic voltammetry, which demonstrate these cyclophanes to be appreciably comparable to the diketophosphanyl systems commonly explored in the context of organic electronic materials; intriguingly, the distinct dikeophosphanyl moieties within the macrocycles appear effectively "insulated" by the macrocycle geometry, rather than acting as a through-conjugate.

2,5-bis[2-(2-phenyl-1,3-oxazol-5-yl)phenyl]-1,3,4-oxadiazole – new sterically hindered high Stokes shift fluorophore sensitive to media viscosity

Abstract New sterically hindered high Stokes shift polyheteroaromatic fluorophore (2,5-bis[2-(2-phenyl-1,3-oxazol-5-yl) phenyl]-1,3,4-oxadiazole, ( 1 ) belonging to the ortho -POPOP family was synthesized and its molecular structure was confirmed by X-ray and NMR data. Like any other ortho -POPOPs, the title molecule is substantially non-planar in the ground state owing to repulsion of its oxazole/oxadiazole cycles introduced in ortho -positions of the inner-chain benzene rings. Thus the intramolecular π-conjugation in 1 molecule is weakened in respect to its planar para -substituted analogs. Intermolecular π – π contacts in the crystalline lattice result in asymmetrization of the oxadiazole–phenyl–oxazole subunits of 1 , which reflects itself in significantly different angles between the planes of azole and their neighboring benzene rings. Quantum-chemical modeling of 1 revealed for this molecule the ground state symmetrization in fluid media with alignment of the inter-ring angles. The significant excited state planarization of the title molecule, which was predicted by our TD-DFT calculations as well, results in partial restoration of the disturbed ground state conjugation, in decrease of the structurally relaxed excited state energy and finally – in theoretically predicted and experimentally observed abnormally high fluorescence Stokes shifts. The excited state conformational changing of 1 requires high amplitude intramolecular motions, which should be affected by the local media viscosity. This was confirmed in our time-resolved fluorescence experiments, which demonstrate decrease of the excited state structural relaxation rate in alcohols of different viscosity: 2-propanol, ethylene glycol and glycerol. Special experiments in toluene–polystyrene system allow us to recommend the investigated compound as potential fluorescent viscosity sensor.

Comprehensive Analysis of Fragment Orbital Interactions to Build Highly π‐Conjugated Thienylene‐Substituted Phenylene Oligomers

π-Conjugated thienylene-phenylene oligomers with fluorinated and dialkoxylated phenylene fragments have been designed and prepared to understand the interactions in fragment orbitals, the influence of the substituents (F, OMe) on the HOMO-LUMO gap, and the role of intramolecular non-covalent cumulative interactions in the construction of π-conjugated nanostructures. Their strong conjugation was also evidenced in the gas phase by UV photoelectron spectroscopy and theoretical calculations. These results can be explained by the crucial role of the relative energetic positions of the π orbitals of the dimethoxyphenylene, which was used to model the dialkoxyphenylene entity, in determining the π/π(*) orbital levels of the fluorinated phenylene entity. Dialkoxyphenylenes raise the HOMO orbitals, whereas fluorinated phenylenes lower the LUMO orbitals in the oligomers. In addition, the presence of S⋅⋅⋅F and H⋅⋅⋅F interactions in the fluorinated phenylene-thienylene compounds add to the S⋅⋅⋅O interactions in the mixed targets and contribute to the full conjugation in the oligomer, inducing weak inter-ring angles between the involved aromatic cycles. These results, which showed extended conjugation of the π system, were corroborated by a narrow HOMO-LUMO gap (according to DFT calculations) and by a relatively strong maximum wavelength (as obtained by TD-DFT calculations and experimental UV/Vis measurements). The crystallographic data of two mixed thienylene-(fluorinated and dialkoxylated phenylene) five-ring oligomers agree with the above results and show the formation of quasi-planar conformations with non-covalent S⋅⋅⋅O, H⋅⋅⋅F, and S⋅⋅⋅F interactions. These studies in the solid and gas phases show the relevance of associating dialkoxyphenylene and fluorinated phenylene fragments with thiophene to lead to oligomers with improved electronic delocalization for electronic or optoelectronic devices.

Six hydrogen bond directed supramolecular adducts formed between racemic-bis-β-naphthol and N-containing aromatic bases

Abstract Studies concentrating on hydrogen bonding between the base of exobidentate bis(imidazole) derivatives, and 2-aminoheterocyclic compounds, and (±)-1,10-binaphthalene-2,2′-diol have led to an increased understanding of the role the aromatic N-containing compounds have in binding with (±)-1,10-binaphthalene-2,2′-diol. Here anhydrous multicomponent adducts of N-containing aromatic bases such as 1,4-bis(N-imidazolyl)butane (L1), 1,3-bis(N-benzimidazolyl)propane (L2), 1,4-bis(N-benzimidazolyl)butane (L3), 1,5-bis(N-benzimidazolyl)-3-oxapentane (L4), 2-amino-4-phenylthiazole (L5), and 2-amino-5,7-dimethyl-1,8-naphthyridine (L6) have been prepared with (±)-1,10-binaphthalene-2,2′-diol (binol). The six crystalline forms reported are cocrystals of which the crystals and complexes were characterized by X-ray diffraction analysis, IR, mp, and elemental analysis. The inter-ring angles (naphthol/naphthol) in the same binol of the six cocrystals ranged from 70.71° to 104.2° as the organic bases varied. In the six cocrystals, the binols exist either as both of the enantiomers of rac-binol or as only of its single enantiomer. All supramolecular architectures of cocrystals 1–6 are stabilized by O–H⋯N hydrogen bonds. In addition other non-conventional interactions (CH–π, CH3–π, NH–π, S–π, and π–π interactions) play an important role in the solid-state packing of co-crystallization as well. These weak interactions combined, all of the six complexes displayed 3D network structure.

Exploiting the information content of dipolar couplings: determination of the temperature dependence of the inter-ring twist angle of biphenyl dissolved in uniaxial mesophases

In the present work, the quite intriguing question of the temperature dependence of the inter-ring angle of biphenyl in fluid condensed phases has been investigated by the proton liquid crystal nuclear magnetic resonance technique. The spectra of the molecule dissolved in three different thermotropic uniaxial solvents (one of which shows also a smectic A phase) at different values of temperature have been analysed by standard procedures, and the resulting temperature-dependent dipolar coupling sets have been rationalised by the additive potential for the treatment of the ordering interactions method, combined with the direct probability description of the torsional curve, in order to obtain the distribution of the twist angle φ for each temperature. The results emphasise a very slight but unequivocal and systematic increase of φM (the most probable value of the dihedral angle) with temperature, so qualitatively confirming what was previously found by a cruder hybrid approach (based on experimental quadrupolar splittings of perdeuteriated biphenyl combined with computer-simulated order parameters) carried out by two of the present authors (Celebre, G.; De Luca, G.; Mazzone, G. J. Mol. Struct. (THEOCHEM) 2005, 728, 209–214).

Jet-cooled vibronic spectroscopy and asymmetric torsional potentials of phenylcyclopentene

The ultraviolet spectroscopy of the S(1) <-- S(0) transition of 1-phenylcyclopentene (PCP) was studied by resonant-two-photon ionization (R2PI), laser-induced fluorescence (LIF) and single vibronic level fluorescence (SVLF). UV-UV hole-burning (UVHB) spectroscopy was used to determine that there is only one spectroscopically distinct conformer in the supersonic expansion. The excitation spectrum shows extensive vibronic structure extending to over 1000 cm(-1) above the electronic origin (34,646 cm(-1)). Much of the vibronic structure is similar to that of styrene and other singly substituted benzene derivatives, with Franck-Condon (FC) activity predominantly in substituent-sensitive benzene modes. Sizeable FC progressions were also found in the inter-ring torsion, reflecting a large displacement in the inter-ring angle upon electronic excitation. No evidence for FC activity in the ring-puckering coordinate is observed. The torsional potentials of the ground and excited states were determined from the experimental transition frequencies by fitting the calculated to the experimental torsional frequency spacings in an automated least-squares fitting procedure. The S(1) torsional potential is a symmetric single-well potential centered around a locally planar equilibrium geometry at a torsional angle of varphi = 0 degrees . The energy levels are reproduced by a cosine term potential function with torsional parameters V(2) = 3765 cm(-1) and V(4) = -183 cm(-1). The S(0) torsional potential possesses a twisted equilibrium geometry that is strongly asymmetric about varphi = 0 degrees due to the non-planarity of the cyclopentene ring. The best-fit potential parameters uses a sin/cos potential function (odd/even), with V = 948 cm(-1), V = -195 cm(-1), V = -162 cm(-1) and V = -268 cm(-1). The shape of the potentials are similar to those predicted by relaxed potential energy scans calculated at the DFT, CIS and TDDFT//CIS levels of theory. The change in the torsional angle varphi upon electronic excitation was determined to be approximately 15 degrees from fits of the displacement delta of the S(0) torsional potential with respect to the S(1) potential. The simulated shift of the S(0) potential with respect to the S(1) potential of approximately 15 degrees is in very good agreement with that obtained from B3LYP calculations.

Di-μ3-oxido-di-μ2-oxido-tetraoxidobis(1,1,2,2-tetramethylethylenedicyclopentadienyl)dimolybdenum(IV)dimolybdenum(VI) hexahydrate

The title compound, [Mo4(C16H20)2O8]·6H2O, is a centrosymmetric ansa-molybdocene complex in which two dinuclear [C2Me4(η5-C5H4)2]Mo(μ2-O)2MoO2 units dimerize by forming two μ3-O bridges between three Mo atoms. The ansa-molybdocene [C2Me4(η5-C5H4)2]Mo unit has a typical bent-sandwich metallocene structure with an inter-ring angle of 127.98 (8)°. The Mo atom in the bridging (μ2-O)(μ3-O)2MoO2 group has a distorted trigonal–bipyramidal coordination. The Mo—(μ3-O) and Mo—(μ2-O) bond distances inside the units [2.0869 (14) and 2.1014 (15) Å, respectively] are slightly longer than the Mo(−x + 1, −y + 1, −z)—(μ3-O) bond distance between the units [1.9986 (14) Å]. The solvent water mol­ecules together with complex O atoms form a network of O—H⋯O hydrogen bonds.

Structural and Electronic Properties of Crown Ether Functionalized Oligothiophenes

Quantum mechanical calculations at the B3LYP level combined with the 6-31G(d) and 6-31+G(d,p) basis sets have been performed on oligomers containing n repeating units (with n ranging from 2 to 8) of three crown ether functionalized polythiophenes, which differ in the size of the macrocycle. Results have been compared with those obtained for poly(3,4-ethylenedioxthiophene), which was calculated at the same theoretical levels. Results indicate that, independently of the size of the ether macrocycle, functionalized oligomers tend to adopt an antiplanar conformation with the inter-ring dihedral angles arranged in trans. Moreover, the rotational profile calculated by scanning the inter-ring angle is not significantly influenced by neither the size of the macrocycle nor its conformation. On the other hand, the electronic properties of the crown ether functionalized polythiophenes, which were obtained by extrapolating the results obtained for the oligomers, were very similar to those of poly(3,4-ethylenedioxythi...

Atomic study of molecular wires composed of thiophene oligomers

In this paper, we study the electron conductance of thiophene oligomers based molecular wires through atomic structures using the first principles method based on density functional theory and nonequilibrium Green's function. The molecular wires are built by sandwiching various thiophene oligomers between two metal electrodes via terminal groups at atomic levels. The effects of alkyl substituents on the thiophene oligomers are modelled by varying inter-ring angles of the oligomers. Thiophene dimers, tetramers and hexamers are used to studied thiophene size effects. The projected orbitals, energy gaps, transmission functions and current-voltage characteristics of the molecular wires are calculated and analyzed. Results show that the molecular wires with the planar structures of thiophene oligomers have larger electron transmission functions, hence better electronic conductance than those with twist structures. The conductance of molecular wires decreases when the chain length of the thiophene oligomer increases. The results can provide guidance for design of thiophene molecular electronic wires and other devices.

The combined use of deuterium NMR and computer simulations for conformational investigation of flexible molecules in nematic solutions

In this paper, we suggest a new methodological approach to get in a very simple way a crude (but meaningful) conformational analysis of flexible molecules in fluid condensed phases (a very interesting matter where inter- and intra-molecular interactions are deeply involved). The test case we have chosen is the never-studied-before temperature dependence of inter-ring angle of biphenyl in a nematic solution. Undemanding 2H NMR experiments were carried out on perdeuterated biphenyl dissolved in the mesophase at different temperatures, to obtain deuterium quadrupolar splittings. Since the experimental data alone are not sufficient to allow the determination of the inter-ring angle for each temperature, they were supplemented with simulated orientational information: this ‘hybrid’ set of data was enough to obtain the searched conformational distribution versus T. The results, showing a very slight tendency of the inter-ring angle to increase with the temperature, lend themselves to immediate interesting speculations and encourages the accomplishment of more sophisticated and expensive experiments to investigate more in detail the phenomenology. In our opinion the suggested methodology, appealing for its easiness, could be useful, for example, for coarse grained conformational investigations of large flexible systems (as, e.g. biomolecules) in liquid media.

The determination of the conformation of the aromatic rings in a lateral fluoro-substituted liquid crystal by 13C NMR spectroscopy

A 13C–{1H} NMR spectrum of 2,2′-difluoro-4″-hexoxy-4-pentyl-[1,1′∶4′,1″]-terphenyl in the nematic phase has been obtained and analysed to yield a set of partially-averaged dipolar couplings, DCFij, which are used to determine the relative conformation of the two fluorinated rings. The probability distribution for the inter-ring angle is found to be peaked at 47.5±2.5° and 122.5±2.5°. The integrated, normalised probability that the inter-ring angle is less than 90° is 0.43.

Photophysical and theoretical studies of naphthalene-substituted oligothiophenes

A comprehensive photophysical characterization of a new class of naphthalene derivatives of the important α-oligothiophenes (αn’s) has been undertaken in solution at room (293 K) and low (77 K) temperature. This includes absorption and fluorescence spectra, fluorescence quantum yields (φF), and lifetimes (τF), as a function of temperature and solvent. Triplet–triplet absorption spectra and triplet formation quantum yields (φT) were also determined. From the above, all the rate constants for the radiative (kF) and radiationless (kIC and kISC) have been calculated. It is shown that the lowest singlet excited state is an allowed π,π* state in all solvents. The results show that although the behavior of the oligomers is similar to their parent compounds (αn’s), significant differences are observed. By comparison of the extinction coefficients of the naph(αn’s) and the (αn’s), a good correlation was found between naph(αn) and α(n+1). On the basis of this proposed pairing, a consistent blue-shift was observed in the absorption maxima between the compounds here considered and the reference α-oligothiophenes. This indicates that there is some significant twist between the naphthalene and the αn chromophores. The most favorable inter-ring angle between the two chromophores, naphthalene and αn, was predicted on the basis of comparison with theory.

Acentric Extended Solids by Self Assembly of 4,4'-Bipyrazolyls The authors gratefully acknowledge support from the Deutsche Forschungsgemeinschaft and the Sächsisches Staatsministerium für Wissenschaft und Kunst.

The inter-ring angle φ of 4,4′-bipyrazolyls, which can be controlled by varying the 3,3′- and 5,5′-substituents, determines their association into different three-dimensional arrays through interaction of their self-complementary hydrogen-bond donor and acceptor sites. Thus, for φ≈90°, a (10,3)-b net is formed (see picture, top), while for φ≈60°, the inherently chiral (10,3)-c net is obtained (see picture, bottom).

Bridging-terminal exchange in ansa-bridged tetrahydroborate niobocene compounds: a density functional study

Density functional calculations on [Nb(η-C 5H 5) 2(η 2-BH 4)], [Nb{H 2Si(η-C 5H 4) 2}(η 2-BH 4)] and [Nb{H 2C(η-C 5H 4) 2}(η 2-BH 4)], show the barrier to terminal-bridging hydrogen exchange decrease as the inter-ring angle increases, in agreement with earlier experimental data. The calculations suggest the bonding of BH 4 weakens as the metallocene unit becomes more bent, and that there is stronger bonding in the transition state as the d yz orbital becomes more accessible.

Photoelectron spectroscopy and electronic structure of the hexaphosphatitanocene [Ti(η5-P3C2But2)2] †

Density functional calculations on [Ti(η5-P3C2But2)2] gave estimates of structural parameters in excellent agreement with experiment and predicted a diamagnetic ground state as has been found. Back donation from the metal to the π LUMO of the ring forming a δ bond accounts for the inter-ring angle and the diamagnetism. The He I photoelectron spectrum of [Ti(η5-P3C2But2)2] is assigned. Agreement between calculated and experimental ionization energies lends support to the detailed orbital analysis that is presented.

A theoretical study of the effect of ansa-bridges on the energy barrier to hydrogen exchange in a series of biscyclopentadienyl tungsten trihydride cations

Density functional calculations have been carried out on the structures and pathway for hydrogen exchange of the tungsten trihydride cations, [W(η-C5H5)2H3]+, I, [W{(η-C5H4)2SiH2}H3]+, II, and [W{(η-C5H4)2CH2}H3]+, III, as models for the characterised trihydride cations [W(η-C5H5)2H3]+, 1, [W{(η-C5H4)2SiMe2}H3]+, 2, and [W{(η-C5H4)2CMe2}H3]+, 3. The most significant difference found for the ground state structures is the increase in inter-ring angle in the order I II>III. Also the ease of the in-plane bending motion decreases in the same order. For III, a dihydrogen hydride structure is found as an intermediate on the bending pathway. The exchange energy barriers for II and III of 63 and 51 kJ mol-1 are consistent with the large temperature dependent H1H coupling constants previously reported for cations 2 and 3, which have been attributed to quantum mechanical exchange coupling. The barrier calculated for I, of 96 kJ mol-1, lies outside the range wherein such unusual coupling is expected and 1 is reported to have a small temperature independent coupling constant. The relative ease of approach calculated for the two hydrogens is also consistent with the view that the quantum mechanical exchange is facilitated by a short tunnelling path. The underlying reasons for the differences found for the series I–III are twofold. As the inter-ring angle increases the rings become more tightly bound and the hydrides less tightly bound. The exchange pathway involves reduction of the metal from a to a configuration, and the d orbital involved becomes more stable on bending the rings.

Electronic Structure of Strained Silicon- and Sulfur-Bridged [1]Ferrocenophanes and an Analogous Dicarbon-Bridged [2]Ferrocenophane: An Investigation by Photoelectron Spectroscopy and Density-Functional Theory

He I and He II photoelectron (PE) spectra of [Fe(η-C5H4)2SiMe2] (1), [Fe(η-C5H3Me)2SiMe2] (2), [Fe(η-C5H4)(η-C5Me4)SiMe2] (3), [Fe(η-C5Me4)2SiMe2] (4), [Fe(η-C5H4)2C2H4] (5), and [Fe(η-C5H4)2S] (6) have been measured and assigned. The d bands of 1−5 show less structure than that of ferrocene, consistent with a loss of degeneracy of the e2 orbitals on bending. Compound 6, which has the largest inter-ring angle of the series, shows two separate d bands. The trend in the first ionization energy closely parallels the variation in oxidation potential. Density functional calculations on 1, 5, and 6 give geometries in good agreement with the structures found from X-ray diffraction. Ionization energies calculated were also in excellent agreement with experiment. Good agreement was also found between the calculated d−d transitions and the position of the first spin-allowed band in the optical spectra of 1 and 6. Estimates of strain energy in bending ferrocene and octamethylferrocene were obtained, and octamethylferrocene was shown to be significantly more difficult to bend. Compounds 1 and 6 were both shown to have a low-lying empty orbital, partially located on the ipso carbon, which is a possible site for nucleophilic attack in the polymerization process undergone by these compounds.

A maximum-entropy analysis of the problem of the rotameric distribution for substituted biphenyls studied by 1H nuclear magnetic resonance spectroscopy in nematic liquid crystals

The statistical principle of maximum entropy is applied to the analysis of dipolar couplings from 1H NMR of nonrigid molecules dissolved in liquid-crystalline phases. A distribution function for the orientational and inter-ring angles is so obtained. The most probable internal angle φ is determined for 4,4′-dichlorobiphenyl (φ=34°) in the nematic phase of I52, 4-pentyl-4′-cyanobiphenyl (φ=32°) and 4′-Br-4-Cl-2,6-difluorobiphenyl (φ=42°) in EBBA. The physical reliability of the distributions determined is discussed. The maximum-entropy treatment seems to indicate a limit for the information on the internal motion obtainable from the experimental data.

Inter-ring dihedral angles in polychlorinated biphenyls from photoelectron spectroscopy

A proposal that the physiological activity of a chlorinated biphenyl is related to its degree of molecular planarity is explored through experimental measurements of inter-ring dihedral angles in the gas phase. A known correlation between the difference between fourth and first ionization energies of substituted biphenyls (via photoelectron spectroscopy), and the thermally averaged inter-ring dihedral angle as established by electron diffraction techniques, is confirmed and exploited for the present purpose. The expectation, based on both qualitative and quantitative theoretical considerations, that increased ortho substitution causes an increase in inter-ring angle, is confirmed. However, the observation that, for 2,2′-substituted halobiphenyls the only observed conformation is the near-syn form, is not easy to explain, and is discussed in terms of a non-bonding attractive force between halogen atoms.