Highly cross-linked bifunctional magnesium porphyrin-imidazolium bromide polymer: Unveiling the key role of co-catalysts proximity for CO2 conversion into cyclic carbonates

Highly cross-linked materials containing an imidazolium salt and magnesium porphyrin, either in the absence (TSP-Mg-imi) or in the presence (7a and 7b) of multi-walled carbon nanotubes (MWCNTs), were synthesized and used as heterogeneous bifunctional catalysts for the conversion of CO2 into cyclic carbonates. The metalloporphyrin moiety acts both as a “covalent swelling agent”, generating hybrids with high surface area, and as a Lewis acid co-catalytic species. TSP-Mg-imi produced excellent conversion and TONMg values, under solvent-free conditions, even at room temperature and with low catalytic loading (0.003 mol%). In terms of conversion and TONMg, TSP-Mg-imi exhibited better catalytic performance compared to a reference homogeneous system, demonstrating that the proximity between the metal centers and the nucleophilic site results in a synergistic effect during the catalytic cycle. The results of the computational study confirmed both the cooperative function and the significance of incorporating a co-catalytic species into the system

Structure influence on charge transport in naphthalenediimide-thiophene copolymers

Reported here is a characterisation of a series of NDI-thiophene copolymers with 1, 2, 3 and 4 thiophene units synthesized using Stille polycondensation of dibromo-naphthalene diimide and the trimethylstannylthiophene monomers. The effect of extension of the thiophene donor group is studied in terms of structure-charge transport correlation. The influence of side chains located on the thiophene units of copolymers with 2 and 4 thiophene units per monomer is also investigated. Charge transport of both signs is studied experimentally in field-effect transistors. Microstructural data obtained by near-edge x-ray absorption fine structure (NEXAFS) and grazing incidence wide-angle x-ray scattering (GIWAXS) is supported by AFM topography scans. UPS and UV-Vis spectroscopy data are employed in measurement of energy levels and changes with annealing temperature are also discussed. Most of the polymers reach excellent electron as well as hole mobility with one copolymer (NDI-T4) exhibiting an especially balanced ambipolar charge transport of 0.03 cm2V-1s-1. An odd-even effect in hole mobility is observed with higher values for polymers with even number of thiophene units. The reported findings indicate that the final charge transport properties are a result of the interplay of many factors, including crystallinity, planarity and linearity of chain, spacing between acceptor units and packing of solubilizing branched side chains.CRM acknowledges support from the Australian Research Council (FT100100275, DP130102616) and thanks Dr. Nigel Kirby and Dr. Steven Mudie of the Australian Synchrotron for technical support. The work in Mons is supported by the European Commission / Région Wallonne (FEDER – Smartfilm RF project), the Interuni-versity Attraction Pole program of the Belgian Federal Science Policy Office (PAI 7/05) and the Programme d’Excellence de la Région Wallonne (OPTI2MAT project). MMS acknowledges support from the Winton Programme for the Physics of Sustainability. MiS acknowledges funding from the Fonds der chemischen In-dustrie.This is the accepted manuscript. The final published version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/cm5033578

White light emitting silsesquioxane based materials: The importance of a ligand with rigid and directional arms

The synthesis of a novel polyhedral oligomeric silsesquioxane functionalized with eight rigid and directional terpyridine-based arms (Ter-POSS) was successfully achieved via a Sonogashira reaction. The POSS based ligand was extensively characterized using different techniques including 1H, 13C and 29Si NMR as well as UV-Vis and fluorescence spectroscopies. The assembly of these nano-caged units in the presence of different transition metal ions (Fe2+, Zn2+ and Cu2+) as well as of a cation from the lanthanides (Eu3+) was investigated using absorption and emission spectroscopies. The final materials display an evident emission in different regions of the visible spectrum as a function of the cation employed. Additional insights into the structural organization of Ter-POSS in the presence of metal cations were obtained via molecular mechanics and molecular dynamics simulations. The polymeric material resulting from the complexation with europium displays a white light emission ascribed to the presence of combined contributions from the blue, green and red regions. The final self-assembled organizations display an increased quantum yield with the highest value (29.6%) obtained in the presence of Zn2+. Moreover, the white-light emitting europium-based nanostructure exhibits one of the highest quantum yields reported in the literature for similar solids

Strong Suppression of Thermal Conductivity in the Presence of Long Terminal Alkyl Chains in Low-Disorder Molecular Semiconductors

While the charge transport properties of organic semiconductors have been extensively studied over the recent years, the field of organics-based thermoelectrics is still limited by a lack of experimental data on thermal transport and of understanding of the associated structure–property relationships. To fill this gap, a comprehensive experimental and theoretical investigation of the lattice thermal conductivity in polycrystalline thin films of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (Cn-DNTT-Cn with n = 0, 8) semiconductors is reported. Strikingly, thermal conductivity appears to be much more isotropic than charge transport, which is confined to the 2D molecular layers. A direct comparison between experimental measurements (3ω–Völklein method) and theoretical estimations (approach-to-equilibrium molecular dynamics (AEMD) method) indicates that the in-plane thermal conductivity is strongly reduced in the presence of the long terminal alkyl chains. This evolution can be rationalized by the strong localization of the intermolecular vibrational modes in C8-DNTT-C8 in comparison to unsubstituted DNTT cores, as evidenced by a vibrational mode analysis. Combined with the enhanced charge transport properties of alkylated DNTT systems, this opens the possibility to decouple electron and phonon transport in these materials, which provides great potential for enhancing the thermoelectric figure of merit ZT

Oxacycle fused [1]benzothieno[3,2-b][1]benzothiophene derivatives: synthesis, electronic structure, electrochemical properties, ionisation potential, and crystal structure

The molecular properties of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) are vulnerable to the structural modifications which in turn are decided by the functionalization of the backbone. Hence versatile synthetic strategies are needed to discover the properties of this molecule. To address this, we have attempted heteroatom (oxygen) functionalization of BTBT by a concise and easily scalable synthesis. Four-fold hydroxy substituted BTBT is the key intermediate, from which the compounds 2,3,7,8- bis(ethylenedioxy)-[1]benzothieno[3,2-b][1]benzothiophene and 2,3,7,8- bis(methylenedioxy)-[1]benzothieno[3,2-b][1]benzothiophene are synthesized. The difference in ether functionalities on the BTBT scaffold influences the ionisation potential values substantially. The crystal structure reveals the transformation of the herringbone motif in bare BTBT towards π stacked columns in the newly synthesized derivatives. The results are further elaborated with the aid of quantum chemical calculations

Design, synthesis, chemical stability, packing, cyclic voltammetry, ionisation potential, and charge transport of [1]benzothieno[3,2-b][1]benzothiophene derivatives

Five new molecular semiconductors that differ from dioctylbenzothienobenzothiophene, by the introduction of ether or thioether side chains, have been synthesized and obtained in good yields. Their availability in sufficient quantities has allowed investigation of their electrochemical behaviour in solution and their electronic properties in solid state. Both ether and thioether compounds oxidise rather easily in solution, but nevertheless, they exhibit rather high ionisation potentials. This is a consequence of their crystal structure. Dioctylthioetherbenzothienobenzothiophene is rather sensitive to oxidation and degrades easily in close to ambient conditions. Dioctylletherbenzothienobenzothiophene is more stable. Its charge carrier mobility remains however rather moderate, on the order of 0.5 cm2/V.s, whereas that of dioctylbenzothienobenzothiophene reached 4 cm2/V.s, in the same conditions. The difference is explained by intrinsic factors as shown by a theoretical modelling

Core charge distribution and self assembly of columnar phases: the case of triphenylenes and azatriphenylenes

<p>Abstract</p> <p>Background</p> <p>The relation betweeen the structure of discotic molecules and columnar properties, a crucial point for the realization of new advanced materials, is still largely unknown. A paradigmatic case is that hexa-alkyl-thio substituted triphenylenes present mesogenic behavior while the corresponding azatriphenylenes, similar in shape and chemical structure, but with a different core charge distribution, do not form any liquid crystalline mesophase. This study is aimed at investigating, with the help of computer simulations techniques, the effects on phase behaviour of changes of the charge distribution in the discotic core.</p> <p>Results</p> <p>We described the shape and the pair, dispersive and electrostatic, interactions of hexa alkyl triphenylenes by uniaxial Gay-Berne discs with embedded point charges. Gay-Berne parameters were deduced by fitting the dispersive energies obtained from an atomistic molecular dynamics simulation of a small sample of hexa-octyl-thio triphenylene molecules in columnar phase, while a genetic algorithm was used to get a minimal set of point charges that properly reproduces the ab anitio electrostatic potential. We performed Monte Carlo simulations of three molecular models: the pure Gay-Berne disc, used as a reference, the Gay-Berne disc with hexa-thio triphenylene point charges, the Gay-Berne disc with hexa-thio azatriphenylene point charges. The phase diagram of the pure model evidences a rich polymorphism, with isotropic, columnar and crystalline phases at low pressure, and the appearance of nematic phase at higher pressure.</p> <p>Conclusion</p> <p>We found that the intermolecular electrostatic potential among the cores is fundamental in sta-bilizing/destabilizing columnar phases; in particular the triphenylene charge distribution stabilizes the columnar structure, while the azatriphenylene distribution suppresses its formation in favor of the nematic phase. We believe the present model could be successfully employed as the basis for coarse-grained level simulations of a wider class of triphenylene derivatives.</p

Fingerprints for Structural Defects in Poly(thienylene vinylene) (PTV): A Joint Theoretical–Experimental NMR Study on Model Molecules

In the field of plastic electronics, low band gap conjugated polymers like poly(thienylene vinylene) (PTV) and its derivatives are a promising class of materials that can be obtained with high molecular weight via the so-called dithiocarbamate precursor route. We have performed a joint experimental- theoretical study of the full NMR chemical shift assignment in a series of thiophene-based model compounds, which aims at (i) benchmarking the quantum-chemical calculations against experiments, (ii) identifying the signature of possible structural defects that can appear during the polymerization of PTV's, namely head-to-head and tail-to-tail defects, and (iii) defining a criterion regarding regioregularity