Computational studies on cyclic [n]paraphenyleneacetylenes using homodesmotic reactions
TL;DR: In this article, a homodesmotic reaction scheme coupled with density functional theory has been used to estimate theoretically strain energies and heats of formation of cyclic [n]paraphenyleneacetylenes ([n]CPPAs) for molecular electronics.
Abstract: Cyclic [n]paraphenyleneacetylenes ([n]CPPAs) are potentially useful compounds for molecular electronics In this article, a homodesmotic reaction scheme coupled with density functional theory has been used to estimate theoretically strain energies and heats of formation of [n]CPPAs Calculations have been done for a series of [n]CPPAs, containing up to ten phenylacetylene units Strain energies of [n]CPPAs decrease, while heats of formation increase steadily with the increase in the number of phenylacetylene units using homodesmotic reaction schemes B3LYP and mPW1PW91 functionals have been used with the Pople basis set 6-31G* to analyze the trends The results are sensitive to the scheme of homodesmotic reaction chosen, thereby necessitating careful chemical consideration before spending considerable computational resources for higher [n]CPPAs not considered here Computational estimates for the ring diameter of [n]CPPAs and absolute entropy have also been obtained here The HOMO-LUMO gaps of the belt sh
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TL;DR: This review gives a comprehensive and strictly chronological treatment of literature reports from the inception of the field, with emphasis on both synthesis and properties of CPPs and related nanohoops.
Abstract: The first synthesis of a cyclic oligophenylene possessing a radial π system was reported in 2008. In the short period that has elapsed since, there has been an ever-increasing level of interest in molecules of this type, as evidenced by the volume of publications in this area. This interest has been driven by the highly unusual properties of these molecules in comparison to their linear oligoarene analogues, as well as the diverse array of potential applications for them. Notably, CPPs and related structures were proposed as viable templates for the bottom-up synthesis of single-walled carbon nanotubes (SWCNTs), a proposition which has recently been realised. This review gives a comprehensive and strictly chronological (by date of first online publication) treatment of literature reports from the inception of the field, with emphasis on both synthesis and properties of CPPs and related nanohoops. (The scope of this review is restricted to molecules possessing a radial π system consisting entirely of subunits which are aromatic in isolation, e.g. CPPs, but not cycloparaphenyleneacetylenes or cyclopolyacetylenes).
319 citations
TL;DR: The structures and strain energies of cycloparaphenylenes (CPPs) have been determined by DFT calculation at the B3LYP/6-31G(d) level of theory and it was found that benzene rings of [12]CPP can rotate rather freely at room temperature.
207 citations
TL;DR: Geometrical parameters, Raman frequencies, and (1)H NMR chemical shifts of [3]CMPA and [4] CMPA are found to be in good agreement with compounds for which there are experimentally available values at the B3LYP/6-31G* level of theory.
Abstract: The thermochemical properties and ring strains in cyclic [n]metaphenyleneacetylenes ([n]CMPAs), butadiyne-bridged [4(n)]metacyclophynes (B-B[4(n)]MCs), and butadiyne-bridged [4(n)]paracyclophynes (B-B[4(n)]PCs) were studied using a homodesmotic reaction scheme coupled with density functional theory (B3LYP/6-31G*, mPW1PW91/6-31G*, and M06-2X/6-31+G**//B3LYP/6-31G*). Strain energies of [n]CMPAs and B-B[4(n)]MCs decrease first from very high values for small rings to become zero when n becomes 6, then increase with n, and finally decrease as n becomes larger than 8. In the case of B-B[4(n)]PCs, strain energies decrease with increasing n. Heats of formation of [n]CMPAs, B-B[4(n)]MCs, and B-B[4(n)]PCs increase steadily with increasing numbers of phenylacetylene and 1-(buta-1,3-diynyl)benzene to reach a near-constant value per unit monomer as n increases. The geometries and (vibrational and nuclear magnetic resonance) spectroscopic properties of [n]CMPAs, B-B[4(n)]MCs, and B-B[4(n)]PCs were also studied. Geometrical parameters, Raman frequencies, and (1)H NMR chemical shifts of [3]CMPA and [4]CMPA are found to be in good agreement with compounds for which there are experimentally available values at the B3LYP/6-31G* level of theory. In addition, electronic structure calculations were carried out for [n]CMPAs, B-B[4(n)]MCs, and B-B[4(n)]PCs. Ring diameters were also calculated for B-B[4(n)]PCs.
16 citations
TL;DR: In this paper, the structures and stabilities of 1,8-anthrylene cyclic oligomers having acetylene or diacetylene linkers were investigated by DFT calculations with M05 and M06 series functionals.
Abstract: The structures and stabilities of 1,8-anthrylene cyclic oligomers having acetylene or diacetylene linkers were investigated by DFT calculations with M05 and M06 series functionals. The structures o...
16 citations
TL;DR: In this paper, a new type of arrangement of grid-shaped organic semiconductors with extremely low values of internal reorganization energies (IREs) for both hole (0.056 eV) and electron transfer processes has been designed and investigated by density functional theory (DFT) calculations.
Abstract: The lower charge mobility of organic semiconductors relative to that of inorganic semiconductors is a thorny problem that still has not been resolved. Here, a new type of arrangement of grid-shaped organic semiconductors with extremely low values of internal reorganization energies (IREs) for both hole (0.056 eV) and electron (0.078 eV) transfer processes has been designed and investigated by density functional theory (DFT) calculations. The structural, thermodynamic and electronic properties of grid spirofluorene (GSF) consisting of four spirobifluorenes have been discussed thoroughly. Our analyses of these unique grid structures indicate that they possess a stringent structure and very weak ring strain energy, and may be easily synthesized in the laboratory. Interestingly, GSF1, GSF2, and GSF9 possess both small hole and lower electron transfer reorganization energies (<0.1 eV), which may originate from their rigid molecular structures. The large π conjugated system in which all of the frontier molecular orbitals are homogeneously delocalized over the entire molecules is another important characteristic of these GSFs. This work reveals that the gridization method is a novel strategy for obtaining materials with low hole and electron transfer reorganization energies.
15 citations
References
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TL;DR: In this article, a semi-empirical exchange correlation functional with local spin density, gradient, and exact exchange terms was proposed. But this functional performed significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
Abstract: Despite the remarkable thermochemical accuracy of Kohn–Sham density‐functional theories with gradient corrections for exchange‐correlation [see, for example, A. D. Becke, J. Chem. Phys. 96, 2155 (1992)], we believe that further improvements are unlikely unless exact‐exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange‐correlation functional containing local‐spin‐density, gradient, and exact‐exchange terms is tested on 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total atomic energies of first‐ and second‐row systems. This functional performs significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
87,732 citations
NEC1
TL;DR: Iijima et al. as mentioned in this paper reported the preparation of a new type of finite carbon structure consisting of needle-like tubes, which were produced using an arc-discharge evaporation method similar to that used for fullerene synthesis.
Abstract: THE synthesis of molecular carbon structures in the form of C60 and other fullerenes1 has stimulated intense interest in the structures accessible to graphitic carbon sheets. Here I report the preparation of a new type of finite carbon structure consisting of needle-like tubes. Produced using an arc-discharge evaporation method similar to that used for fullerene synthesis, the needles grow at the negative end of the electrode used for the arc discharge. Electron microscopy reveals that each needle comprises coaxial tubes of graphitic sheets, ranging in number from 2 up to about 50. On each tube the carbon-atom hexagons are arranged in a helical fashion about the needle axis. The helical pitch varies from needle to needle and from tube to tube within a single needle. It appears that this helical structure may aid the growth process. The formation of these needles, ranging from a few to a few tens of nanometres in diameter, suggests that engineering of carbon structures should be possible on scales considerably greater than those relevant to the fullerenes. On 7 November 1991, Sumio Iijima announced in Nature the preparation of nanometre-size, needle-like tubes of carbon — now familiar as 'nanotubes'. Used in microelectronic circuitry and microscopy, and as a tool to test quantum mechanics and model biological systems, nanotubes seem to have unlimited potential.
39,086 citations
TL;DR: In this article, the authors proposed a truncated icosahedron, a polygon with 60 vertices and 32 faces, 12 of which are pentagonal and 20 hexagonal.
Abstract: During experiments aimed at understanding the mechanisms by which long-chain carbon molecules are formed in interstellar space and circumstellar shells1, graphite has been vaporized by laser irradiation, producing a remarkably stable cluster consisting of 60 carbon atoms. Concerning the question of what kind of 60-carbon atom structure might give rise to a superstable species, we suggest a truncated icosahedron, a polygon with 60 vertices and 32 faces, 12 of which are pentagonal and 20 hexagonal. This object is commonly encountered as the football shown in Fig. 1. The C60 molecule which results when a carbon atom is placed at each vertex of this structure has all valences satisfied by two single bonds and one double bond, has many resonance structures, and appears to be aromatic. Before 1985, it was generally accepted that elemental carbon exists in two forms, or allotropes: diamond and graphite. Then, Kroto et al. identified the signature of a new, stable form of carbon that consisted of clusters of 60 atoms. They called this third allotrope of carbon 'buckminsterfullerene', and proposed that it consisted of polyhedral molecules in which the atoms were arrayed at the vertices of a truncated icosahedron. In 1990, the synthesis of large quantities of C60 [see Nature 347, 354–358 (1990)] confirmed this hypothesis.
13,394 citations
TL;DR: In this article, the 631G* and 6 31G* basis sets were extended through the second-row of the periodic table and the Hartree-Fock wave functions were used to obtain the equilibrium geometries for one-heavy-atom hydrides.
Abstract: The 6‐31G* and 6‐31G** basis sets previously introduced for first‐row atoms have been extended through the second‐row of the periodic table. Equilibrium geometries for one‐heavy‐atom hydrides calculated for the two‐basis sets and using Hartree–Fock wave functions are in good agreement both with each other and with the experimental data. HF/6‐31G* structures, obtained for two‐heavy‐atom hydrides and for a variety of hypervalent second‐row molecules, are also in excellent accord with experimental equilibrium geometries. No large deviations between calculated and experimental single bond lengths have been noted, in contrast to previous work on analogous first‐row compounds, where limiting Hartree–Fock distances were in error by up to a tenth of an angstrom. Equilibrium geometries calculated at the HF/6‐31G level are consistently in better agreement with the experimental data than are those previously obtained using the simple split‐valance 3‐21G basis set for both normal‐ and hypervalent compounds. Normal‐mode vibrational frequencies derived from 6‐31G* level calculations are consistently larger than the corresponding experimental values, typically by 10%–15%; they are of much more uniform quality than those obtained from the 3‐21G basis set. Hydrogenation energies calculated for normal‐ and hypervalent compounds are in moderate accord with experimental data, although in some instances large errors appear. Calculated energies relating to the stabilities of single and multiple bonds are in much better accord with the experimental energy differences.
6,870 citations
TL;DR: In this paper, scaling factors for fundamental vibrational frequencies, low-frequency vibrations, zero-point vibrational energies (ZPVE), and thermal contributions to enthalpy and entropy from harmonic frequencies determined at 19 levels of theory have been derived through a least-squares approach.
Abstract: Scaling factors for obtaining fundamental vibrational frequencies, low-frequency vibrations, zero-point vibrational energies (ZPVE), and thermal contributions to enthalpy and entropy from harmonic frequencies determined at 19 levels of theory have been derived through a least-squares approach. Semiempirical methods (AM1 and PM3), conventional uncorrelated and correlated ab initio molecular orbital procedures [Hartree−Fock (HF), Moller−Plesset (MP2), and quadratic configuration interaction including single and double substitutions (QCISD)], and several variants of density functional theory (DFT: B-LYP, B-P86, B3-LYP, B3-P86, and B3-PW91) have been examined in conjunction with the 3-21G, 6-31G(d), 6-31+G(d), 6-31G(d,p), 6-311G(d,p), and 6-311G(df,p) basis sets. The scaling factors for the theoretical harmonic vibrational frequencies were determined by a comparison with the corresponding experimental fundamentals utilizing a total of 1066 individual vibrations. Scaling factors suitable for low-frequency vib...
6,287 citations