Getting excited: Challenges in quantum-classical studies of excitons in polymeric systems

A combination of classical molecular dynamics (MM/MD) and quantum chemical calculations based on the density functional theory (DFT) was performed to describe conformational properties of diphenylethyne (DPE), methylated-DPE and poly para phenylene ethynylene (PPE). DFT calculations were employed to improve and develop force field parameters for MM/MD simulations. Many-body Green's functions theory within the GW approximation and the Bethe-Salpeter equation were utilized to describe excited states of the systems. Reliability of the excitation energies based on the MM/MD conformations was examined and compared to the excitation energies from DFT conformations. The results show an overall agreement between the optical excitations based on MM/MD conformations and DFT conformations. This allows for calculation of excitation energies based on MM/MD conformations

Complex-band structure: a method to determine the off-resonant electron transport in oligomers

We validate that off-resonant electron transport across {\it ultra-short} oligomer molecular junctions is characterised by a conductance which decays exponentially with length, and we discuss a method to determine the damping factor via the energy spectrum of a periodic structure as a function of complex wavevector. An exact mapping to the complex wavevector is demonstrated by first-principle-based calculations of: a) the conductance of molecular junctions of phenyl-ethynylene wires covalently bonded to graphitic ribbons as a function of the bridge length, and b) the complex-band structure of poly-phenyl-ethynylene.Comment: version to appear in Chem Phys Lett; 8 pages, 4 figures; minor changes to the 06/08/03 submission (nomenclature and added concluding remark

Solid-state sensory properties of Calix-Poly(Phenylene Ethynylene)s toward nitroaromatic explosives

This study is primarily focused in establishing the solid-state sensory abilities of several luminescent polymeric calix[4]arene-based materials toward selected nitroaromatic compounds (NACs), creating the foundations for their future application as high performance materials for detection of high explosives. The phenylene ethynylene-type polymers possessing bis-calix[4]arene scaffolds in their core were designed to take advantage of the known recognition abilities of calixarene compounds toward neutral guests, particularly in solid-state, therefore providing enhanced sensitivity and selectivity in the sensing of a given analyte. It was found that all the calix[4]arene-poly(para-phenylene ethynylene)s here reported displayed high sensitivities toward the detection of nitrobenzene, 2,4-dinitrotoluene and 2,4,6-trinitrotoluene (TNT). Particularly effective and significant was the response of the films (25-60 nm of thickness) upon exposure to TNT vapor (10 ppb): over 50% of fluorescence quenching was achieved in only 10 s. In contrast, a model polymer lacking the calixarene units showed only reduced quenching activity for the same set of analytes, clearly highlighting the relevance of the macrocyclics in promoting the signaling of the transduction event. The films exhibited high photostability (less than 0.5% loss of fluorescence intensity up to 15 min of continuous irradiation) and the fluorescence quenching sensitivity could be fully recovered after exposure of the quenched films to saturated vapors of hydrazine (the initial fluorescence intensities were usually recovered within 2-5 min of exposure to hydrazine)

Methods of Attaching or Grafting Carbon Nanotubes to Silicon Surfaces and Composite Structures Derived Therefrom

The present invention is directed toward methods of attaching or grafting carbon nanotubes (CNTs) to silicon surfaces. In some embodiments, such attaching or grafting occurs via functional groups on either or both of the CNTs and silicon surface. In some embodiments, the methods of the present invention include: (1) reacting a silicon surface with a functionalizing agent (such as oligo(phenylene ethynylene)) to form a functionalized silicon surface; (2) dispersing a quantity of CNTs in a solvent to form dispersed CNTs; and (3) reacting the functionalized silicon surface with the dispersed CNTs. The present invention is also directed to the novel compositions produced by such methods

Strategies for synthesis of yardsticks and abaci for nanometre distance measurements by pulsed EPR

Silvia Valera is grateful for support by EPSRC and Bela E. Bode acknowledges support by EastCHEM.Pulsed electron paramagnetic resonance (EPR) techniques have been found to be an efficient tool for elucidation of structure in complex biological systems as they give access to distances in the nanometre range. These measurements can provide additional structural information such as relative orientations, structural flexibility or aggregation states. A wide variety of model systems for calibration and optimisation of pulsed experiments has been synthesised. Their design is based on mimicking biological systems or materials in specific properties such as the distances themselves and the distance distributions. Here, we review selected approaches to the synthesis of chemical systems bearing two or more spin centres, such as nitroxide or trityl radicals, metal ions or combinations thereof and sketch their application in pulsed EPR distance measurements.Publisher PDFPeer reviewe

Cooperative effects in the detection of a nitroaliphatic liquid explosive and na explosive taggant in the vapor phase by calix[4]arene-based carbazole-containing conjugated polymers

Two fluorescent molecular receptor based conjugated polymers were used in the detection of a nitroaliphatic liquid explosive (nitromethane) and an explosive taggant (2,3-dimethyl-2,3-dinitrobutane) in the vapor phase. Results have shown that thin films of both polymers display remarkably high sensitivity and selectivity toward these analytes. Very fast, reproducible, and reversible responses were found. The unique behavior of these supramolecular host systems is ascribed to cooperativity effects developed between the calix[4] arene hosts and the phenylene ethynylene-carbazolylene main chains. The calix[4]-arene hosts create a plethora of host-guest binding sites along the polymer backbone, either in their bowl-shaped cavities or between the outer walls of the cavity, to direct guests to the area of the transduction centers (main chain) at which favorable photoinduced electron transfer to the guest molecules occurs and leads to the observed fluorescence quenching. The high tridimensional porous nature of the polymers imparted by the bis-calixarene moieties concomitantly allows fast diffusion of guest molecules into the polymer thin films

Electrical characterization of single molecule and Langmuir-Blodgett monomolecular films of a pyridine-terminated oligo(phenylene-ethynylene) derivative

Monolayer Langmuir–Blodgett (LB) films of 1,4-bis(pyridin-4-ylethynyl)benzene (1) together with the “STM touch-to-contact” method have been used to study the nature of metal–monolayer–metal junctions in which the pyridyl group provides the contact at both molecule–surface interfaces. Surface pressure vs area per molecule isotherms and Brewster angle microscopy images indicate that 1 forms true monolayers at the air–water interface. LB films of 1 were fabricated by deposition of the Langmuir films onto solid supports resulting in monolayers with surface coverage of 0.98 × 10−9 mol·cm−2. The morphology of the LB films that incorporate compound 1 was studied using atomic force microscopy (AFM). AFM images indicate the formation of homogeneous, monomolecular films at a surface pressure of transference of 16 mN·m−1. The UV–vis spectra of the Langmuir and LB films reveal that 1 forms two dimensional J-aggregates. Scanning tunneling microscopy (STM), in particular the “STM touch-to-contact” method, was used to determine the electrical properties of LB films of 1. From these STM studies symmetrical I–V curves were obtained. A junction conductance of 5.17 × 10−5 G 0 results from the analysis of the pseudolinear (ohmic) region of the I–V curves. This value is higher than that of the conductance values of LB films of phenylene-ethynylene derivatives contacted by amines, thiols, carboxylate, trimethylsilylethynyl or acetylide groups. In addition, the single molecule I–V curve of 1 determined using the I(s) method is in good agreement with the I–V curve obtained for the LB film, and both curves fit well with the Simmons model. Together, these results not only indicate that the mechanism of transport through these metal–molecule–metal junctions is non-resonant tunneling, but that lateral interactions between molecules within the LB film do not strongly influence the molecule conductance. The results presented here complement earlier studies of single molecule conductance of 1 using STM-BJ methods, and support the growing evidence that the pyridyl group is an efficient and effective anchoring group in sandwiched metal–monolayer–metal junctions prepared under a number of different conditions.S. M., M. C. L, and P. C. are grateful for financial assistance from Ministerio de Economía y Competitividad from Spain in the framework of project CTQ2012-33198 and support from DGA and Fondos Feder for funding the Platon research group. S. M. also thanks his JIUZ-2013-CIE-05 grant. S. M and P. C. are grateful for the award of the CTQ2013-50187-EXP grant. P. J. L. thanks EPSRC for funding and also gratefully acknowledges support from the Australian Research Council (DP 140100855) and the award of the Future Fellowship (FT120100073). R. J. N. and S. J. H. thank EPSRC for funding (grant EP/H035184/1 and EP/K007785/1).Peer Reviewe

Solvent Molding of Organic Morphologies Made of Supramolecular Chiral Polymers

12sihe self-assembly and self-organization behavior of uracil-conjugated enantiopure (R)- or (S)-1,1'-binaphthyl-2,2'-diol (BINOL) and a hydrophobic oligo(p-phenylene ethynylene) (OPE) chromophore exposing 2,6-di(acetylamino)pyridine termini are reported. Systematic spectroscopic (UVvis, CD, fluorescence, NMR, and SAXS) and microscopic studies (TEM and AFM) showed that BINOL and OPE compounds undergo triple H-bonding recognition, generating different organic nanostructures in solution. Depending on the solvophobic properties of the liquid media (toluene, CHCl3, CHCl3/CHX, and CHX/THF), spherical, rod-like, fibrous, and helical morphologies were obtained, with the latter being the only nanostructures expressing chirality at the microscopic level. SAXS analysis combined with molecular modeling simulations showed that the helical superstructures are composed of dimeric double-cable tape-like structures that, in turn, are supercoiled at the microscale. This behavior is interpreted as a consequence of an interplay among the degree of association of the H-bonded recognition, the vapor pressure of the solvent, and the solvophobic/solvophilic character of the supramolecular adducts in the different solutions under static and dynamic conditions, namely solvent evaporation conditions at room temperature.partially_openopenĐorđević, Luka; Marangoni, Tomas; Miletić, Tanja; Rubio-Magnieto, Jenifer; Mohanraj, John; Amenitsch, Heinz; Pasini, Dario; Liaros, Nikos; Couris, Stelios; Armaroli, Nicola; Surin, Mathieu; Bonifazi, DavideĐorđević, Luka; Marangoni, Tomas; Miletic, Tanja; Rubio Magnieto, Jenifer; Mohanraj, John; Amenitsch, Heinz; Pasini, Dario; Liaros, Nikos; Couris, Stelios; Armaroli, Nicola; Surin, Mathieu; Bonifazi, David

ポリアニリンならびにその誘導体の合成に関する研究

筑波大学 (University of Tsukuba)201