| 1. |
- Danila, Ion, et al.
(författare)
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Hierarchical Chiral Expression from the Nano- to Mesoscale in Synthetic Supramolecular Helical Fibers of a Nonamphiphilic C(3)-Symmetrical pi-Functional Molecule
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 133:21, s. 8344-8353
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Tidskriftsartikel (refereegranskat)abstract
- The controlled preparation of chiral structures is a contemporary challenge for supramolecular science because of the interesting properties that can arise from the resulting materials, and here we show that a synthetic nonamphiphilic C(3) compound containing pi-functional tetrathiafulvalene units can form this kind of object. We describe the synthesis, characterization, and self-assembly properties in solution and in the solid state of the enantiopure materials. Circular dichroism (CD) measurements show optical activity resulting from the presence of twisted stacks of preferential helicity and also reveal the critical importance of fiber nucleation in their formation. Molecular mechanics (MM) and molecular dynamics (MD) simulations combined with CD theoretical calculations demonstrate that the (5) enantiomer provides the (M) helix, which is more stable than the (P) helix for this enantiomer. This relationship is for the first time established in this family of C(3) symmetric compounds. In addition, we show that introduction of the "wrong" enantiomer in a stack decreases the helical reversal barrier in a nonlinear manner, which very probably accounts for the absence of a "majority rules" effect. Mesoscopic chiral fibers, which show inverted helicity, i.e. (P) for the (S) enantiomer and (M) for the (R) one, have been obtained upon reprecipitation from dioxane and analyzed by optical and electronic microscopy. The fibers obtained with the racemic mixture present, as a remarkable feature, opposite homochiral domains within the same fiber, separated by points of helical reversal. Their formation can be explained through an "oscillating" crystallization mechanism. Although C(3) symmetric disk-shaped molecules containing a central benzene core substituted in the 1,3,5 positions with 3,3'-diamido-2,2'-bipyridine based wedges have shown peculiar self-assembly properties for amphiphilic derivatives, the present result shows the benefits of reducing the nonfunctional part of the molecule, in our case with short chiral isopentyl chains. The research reported herein represents an important step toward the preparation of functional mesostructures with controlled helical architectures.
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| 2. |
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| 3. |
- Pop, Flavia, et al.
(författare)
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Hierarchical Self-Assembly of Supramolecular Helical Fibres from Amphiphilic C3-Symmetrical Functional Tris(tetrathiafulvalenes)
- 2014
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Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlag. - 0947-6539 .- 1521-3765. ; 20:52, s. 17443-17453
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Tidskriftsartikel (refereegranskat)abstract
- The preparation and self-assembly of the enantiomers of a series of C-3-symmetric compounds incorporating three tetrathiafulvalene (TTF) residues is reported. The chiral citronellyl and dihydrocitronellyl alkyl chains lead to helical one dimensional stacks in solution. Molecular mechanics and dynamics simulations combined with experimental and theoretical circular dichroism support the observed helicity in solution. These stacks self-assemble to give fibres that have morphologies that depend on the nature of the chiral alkyl group and the medium in which the compounds aggregate. An inversion of macroscopic helical morphology of the citronellyl compound is observed when compared to analogous 2-methylbutyl chains, which is presumably a result of the stereogenic centre being further away from the core of the molecule. This composition still allows both morphologies to be observed, whereas an achiral compound shows no helicity. The morphology of the fibres also depends on the flexibility at the chain ends of the amphiphilic components, as there is not such an apparently persistent helical morphology for the dihydrocitronellyl derivative as for that prepared from citronellyl chains.
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| 4. |
- Rodriguez-Martinez, Xabier, et al.
(författare)
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Microfluidic-Assisted Blade Coating of Compositional Libraries for Combinatorial Applications: The Case of Organic Photovoltaics
- 2020
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Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 10:33
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Tidskriftsartikel (refereegranskat)abstract
- Microfluidic technologies are highly adept at generating controllable compositional gradients in fluids, a feature that has accelerated the understanding of the importance of chemical gradients in biological processes. That said, the development of versatile methods to generate controllable compositional gradients in the solid-state has been far more elusive. The ability to produce such gradients would provide access to extensive compositional libraries, thus enabling the high-throughput exploration of the parametric landscape of functional solids and devices in a resource-, time-, and cost-efficient manner. Herein, the synergic integration of microfluidic technologies is reported with blade coating to enable the controlled formation of compositional lateral gradients in solution. Subsequently, the transformation of liquid-based compositional gradients into solid-state thin films using this method is demonstrated. To demonstrate efficacy of the approach, microfluidic-assisted blade coating is used to optimize blending ratios in organic solar cells. Importantly, this novel technology can be easily extended to other solution processable systems that require the formation of solid-state compositional lateral gradients.
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| 5. |
- Oliveras-Gonzalez, Cristina, et al.
(författare)
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Large Synthetic Molecule that either Folds or Aggregates through Weak Supramolecular Interactions Determined by Solvent
- 2019
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Ingår i: ACS Omega. - : AMER CHEMICAL SOC. - 2470-1343. ; 4:6, s. 10108-10120
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Tidskriftsartikel (refereegranskat)abstract
- Weak noncovalent interactions between large disclike molecules in poorly solvating media generally lead to the formation of fibers where the molecules stack atop one another. Here, we show that a particular chiral spacing group between large aromatic moieties, which usually lead to columnar stacks, in this case gives rise to an intramolecularly folded structure in relatively polar solvents, but in very apolar solvents forms finite aggregates. The molecule that displays this behavior has a C-3 symmetric benzene-1,3,5-tris(3,3-diamido-2,2-bipyridine) (BTAB) core with three metalloporphyrin units appended to it through short chiral spacers. Quite well-defined chromophore arrangements are evident by circular dichroism (CD) spectroscopy of this compound in solution, where clear exciton coupled bands of porphyrins are observed. In more polar solvents where the molecules are dispersed, a relatively weak CD signal is observed as a result of intramolecular folding, a feature confirmed by molecular modeling. The intramolecular folding was confirmed by measuring the CD of a C-2 symmetric analogue. The C-3 symmetric BTAB cores that would normally be expected to stack in a chiral arrangement in apolar solvents show no indication of CD, suggesting that there is no transfer of chirality through it (although the expected planar conformation of the 2,2-bipyridine unit is confirmed by NMR spectroscopy). The incorporation of the porphyrins on the 3,3-diamino-2,2-bipyridine moiety spaced by a chiral unit leaves the latter incapable of assembling through supramolecular pi-pi stacking. Rather, modeling indicates that the three metalloporphyrin units interact, thanks to van der Waals interactions, favoring their close interactions over that of the BTAB units. Atomic force microscopy shows that, in contrast to other examples of molecules with the same core, disclike aggregates (rather than fibrillar one dimensional aggregates) are favored by the C-3 symmetric molecule. The closed structures are formed through nondirectional interlocking of porphyrin rings. The chiral spacer between the rigid core and the porphyrin moieties is undoubtedly important in determining the outcome in polar or less polar solvents, as modeling shows that this joint in the molecule has two favored conformations that render the molecule relatively flat or convex.
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| 6. |
- Schall, Anna P., et al.
(författare)
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Photoconductivity of Nanofilaments That are Self-Assembled from a Porphyrin with Long Alkyl-Chain Substituents
- 2015
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 119:46, s. 26154-26163
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectronically active nanostructures that are Self-assembled from organic rnolecules hold the prortu se of tailored functionality.with simple and inexpensive production. Comparison of nanoWires assembled from related componnds can give important insightS into the details of self-assembly and the,conduction meehanisms. We report the photoconductivity of nanofibers that are self-assembled from a porphyrin With long alkyl substituents. In contrast to previously studied porphyrin nanowires, the photoconductivity increases as atthospheric O-2 is increased. This can be explained-using the same model aS used in the previous studies, by assuming a different, line-up of the bands of the nanofilaments. with the electrode Fermi level. However, this model does not explain our observation that-at O-2 concentrations above 1%, the conduction increases with continued- illunation; this may be due to photoactivation of shallow O-2 adsorption sites. The overall conduction level is low even at high O-2 Concentration, because the alkyl substituents form an insulating sheath around the rianofibers. Such inSulation could be valuable in applications where it would prevent cross-talk between signal S darried in different nanofilaments. Schottky barriers at the interface between- organic nanostructures and electrodes strongly affect conduction and photoconduction, and are strongly influenced by atmospheric gases such, as O-2.
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