Molecular and electronic structures of bipolaron in poly-para-phenylene in terms of molecular orbital symmetry

The molecular structures of the model systems of the polaron and the bipolaron in poly-para-phenylene (PPP) were calculated by an ab initio molecular orbital (MO) method with fairly sophisticated approximations. The calculated models are monocations, dications, monoanions and dianions of biphenyl, para-terphenyl, para-quaterphenyl, para-quinquephenyl and para-hexaphenyl. The calculations show that the longer the PPP oligomer is, the stronger is the tendency to take on a non-planar twisting structure. This was accounted for by the combination of repulsions between proximate ortho-hydrogen atoms with resonance interactions between benzene π MOs. The magnitude of the resonance interactions was assessed by using the symmetry of benzene π MOs as well as an analytical Hückel solution of the π MO for polyene. In addition, negatively charged polarons and bipolarons were found to have a stronger tendency to take on a planar structure than positively charged ones. This result was also explained by comparing the benzene π HOMO with the benzene π LUMO. Received: 30 June 1998 / Accepted: 9 September 1998 / Published online: 23 February 1999     

Isolation and structure of four new ceramides from the starfish Luidia maculata

A new sphingosine-type ceramide LMCer-1-1 (1) and three new phytosphingosine-type ceramides, LMCer-2-1 (2), LMCer-2-6 (3), and LMCer-2-7 (4), were isolated from the anti-hyperglycemic active ceramide molecular species LMCer-1 and LMCer-2, obtained from the less polar fraction of the chloroform-methanol extract of the whole bodies of Luidia maculata. The structures of these ceramides were determined on the basis of chemical and spectroscopic evidence as: (2S,3R,4E,2'R)-2-(2-hydroxyhexadecanoylamino)-16-methyl-4-octadecene-1,3-diol (1), (2S,3S,4R,2'R)-2-(2-hydroxyhexadecanoylamino)-16-methyl-octadecane-1,3,4-triol (2), (2S,3S,4R,2'R)-2-(2-hydroxydocosanoylamino)-hexadecane-1,3,4-triol (3), and (2S,3S,4R,2'R)-2-(2-hydroxydocosanoylamino)-14-methyl-hexadecane-1,3,4-triol (4).     

Molecular design of a π‐conjugated single‐chain electronically conductive polymer

This study demonstrates that single‐chain π‐conjugated systems can be made electrically conductive by modifying the molecular structures of both ends of the oligomers making up a polymer. That is, the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps of a fairly long polyyne‐type oligomer with appropriately modified molecular structures at both ends are found to be on the order of thermal energy by calculations using density functional theory (DFT) with B3LYP functionals. This result applies to molecular structures with characteristic bond alternations. The peculiar bond alternations are caused by competition between two effects of the bond alternations of the two mutually perpendicular π‐conjugated systems, which partially cancel each other out. It is probable that we can design one‐dimensional polymers with HOMO–LUMO gaps small enough to be conductive by combining the above‐mentioned oligomers with each other as monomer units in the polymer. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Mechanochromic Luminescence (MCL) of Purely Organic Two-Component Dyes: Wide-Range MCL over 300 nm and Two-Step MCL by Charge-Transfer Complexation

Despite recent extensive studies on mechanochromic luminescence (MCL), rational control over the magnitude of the emission-wavelength shift in response to mechanical stimuli remains challenging. In the present study, a two-component donor-acceptor approach has been applied to create a variety of organic MCL composites that exhibit remarkable emission-wavelength switching. Dibenzofuran-based bis(1-pyrenylmethyl)diamine and typical organic fluorophores have been employed as donor and acceptor dyes, respectively. Outstanding wide-range MCL with an emission-wavelength shift of over 300 nm has been achieved by mixing the diamine with 3,4,9,10-perylenetetracarboxylic diimide. Unprecedented two-step MCL in response to mechanical stimuli of different intensity has also been realized for a two-component mixture with 9,10-anthraquinone. Fluorescence microscopy observations at the single-particle level revealed that the segregation and mixing of the two-component dyes contribute to the stimuli-responsive emission-color switching of the MCL composites.     

Bridged silver(I) complexes of the polycyclic aromatic compounds tetraphenylethylene and 1,1,4,4-tetraphenyl-1,3-butadiene

For the purpose of investigating the coordination behavior of the sterically congested alkenes and exploring the possibility of cofacial complexation in the polycyclic aromatic system for formation of extended polymeric networks, tetraphenylethylene (tphe) and 1,1,4,4-tetraphenyl-1,3-butadiene (tphb) have been studied with regard to their complexation with a silver(I) ion. The crystal structures of [Ag(tphe)(ClO4)(p-xylene)], [Ag2(tphe)(ClO4)2], [Ag4(tphe)(CF3SO3)4], [Ag2(tphb)(ClO4)2], and [Ag2(tphb)(CF3SO3)2], together with the metal-free ligands tphe and tphb, have been determined by single-crystal X-ray diffraction. The pi-electron-rich cleft in organic components is found to offer a potential site for complexation, which can be utilized to generate an interesting array of organometallic compounds with one- and two-dimensional frameworks.     

A novel trinuclear palladium cluster compound: di‐μ3‐chloro‐tris­[chloro(tri­phenyl­phosphine‐P)­palladium] acetone solvate

The title triangular tripalladium cluster, [Pd₃­Cl₅­(C₁₈­H₁₅P)₃]·­C₃H₆O, (I), has a trigonal‐bipyramidal framework of Pd₃(μ₃‐Cl)₂, with the two Cl atoms in apical positions. Each Pd atom in the framework has two additional coordination sites to establish square‐planar cis‐PdL₂(μ₃‐Cl)₂ geometry. Three P atoms are located on the same side of the plane defined by the Pd₃ triangle, which leads to a pseudo‐C_3v symmetry for the core framework of Pd₃(μ₃‐Cl)₂P₃Cl₃. The average Pd—Cl distance trans to PPh₃ is 2.473 (8) Å, which is significantly longer than the average Pd—Cl distance of 2.294 (4) Å for those trans to terminal Cl, due to the strong trans effect of a P atom compared with a Cl atom. Compound (I) has 49 valence electrons and shows a rhombic electron‐spin resonance signal, indicating an S = ½ ground state.     

Highly accurate O(N) method for delocalized systems

The elongation method, developed in our groups, is an ab initio method approaching order O(N) type scalability with high efficiency and high accuracy (error <10^?8?au/atom in total energy compared to the conventional calculation) that can be applied to any one-dimensional (polymer), two-dimensional (surface) or three-dimensional (solid material) systems. For strongly delocalized systems, however, the accuracy of the original elongation method for the targeted entire systems declines by approximately two orders of magnitude in the total energy as compared to the value obtained by the earlier implemented version of the elongation method for nondelocalized systems. The relatively small differences (10^?6?C10^?8 au) between the elongation method and conventional method total energies have caused more serious errors in the second hyperpolarizability, ??, especially in nano-scale systems which have accompanying strong delocalization. In order to solve this problem, we have incorporated a simple correction technique based on an additional ??orbital basis?? to the ??region basis?? in our original elongation method procedures. Some not so-well-localized orbitals are incorporated into the interaction with the attacking molecule. This treatment has been applied to some model nano- and bio-systems that previously have shown strong delocalization, and the high accuracy in the energy obtained for nonstrongly delocalized systems was retained even for the strongly delocalized systems, both for the energies and for the second hyperpolarizabilities. This is a major breakthrough and now expands the systems for which the elongation method can be used to calculate and predict second-order nonlinear optical properties for delocalized systems.     

Palladium doping of magic gold cluster Au38(SC2H4Ph)24: formation of Pd2Au36(SC2H4Ph)24 with higher stability than Au38(SC2H4Ph)24

A phenylethanethiolate-protected Pd(2)Au(36)(SC(2)H(4)Ph)(24) cluster, which is a two-Pd atom-doped cluster of the well studied magic gold cluster Au(38)(SC(2)H(4)Ph)(24), was synthesized in high purity and its stability was investigated. The results demonstrate that Pd(2)Au(36)(SC(2)H(4)Ph)(24) is more stable than Au(38)(SC(2)H(4)Ph)(24) against degradation in solution and core etching by thiols.     

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