Help! Asia (Blue Nature vs Stacccato Mix) - Various - February 2005 Part 1
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Help us improve our products. Sign up to take part. A Nature Research Journal. The design of molecular systems with high-fidelity self-assembly pathways that include several levels of hierarchy is of primary importance for the understanding of structure-function relationships, as well as for controlling the functionality of organic materials. Reported herein is a high-fidelity self-assembly system that comprises two hydrogen-bonding molecular semiconductors with regioisomerically attached short alkyl chains.
Despite the availability of both discrete cyclic and polymeric linear hydrogen-bonding motifs, the two regioisomers select one of the two motifs in homogeneous solution as well as at the 2D-confined liquid-solid interface. This selectivity arises from the high directionality of the involved hydrogen-bonding interactions, which renders rerouting to other self-assembly pathways difficult.
In thin films and in the bulk, the resulting hydrogen-bonded assemblies further organize into the expected columnar and lamellar higher-order architectures via solution processing. The contrasting organized structures of these regioisomers are reflected in their notably different miscibility with soluble fullerene derivatives in the solid state.
Thus, electron donor-acceptor blend films deliver a distinctly different photovoltaic performance, despite their virtually identical intrinsic optoelectronic properties.
Currently, we attribute this high-fidelity control via self-assembly pathways to the molecular design of these supramolecular semiconductors, which lacks structure-determining long aliphatic chains. These flexible units not only increase the kinetic stability of the assembled structures under specific conditions, but also influence thermodynamically stable structures during their transfer from solution to the bulk 41314 Moreover, a thermal treatment in the bulk may further affect the self-assembled structures by transferring the aliphatic chains into the molten state 16 Such a design should be particularly effective for systems that are based on directional hydrogen-bonding interactions, where usually a drastic structural alteration is induced by the rearrangement of the hydrogen-bonding motif upon increasing the level of self-assembly hierarchy or by applying external stimuli 212223 Such regioisomerically attached alkyl chains also give Help!
Asia (Blue Nature vs Stacccato Mix) - Various - February 2005 Part 1 to different molecular conformations due to steric demand, which results in Help!
Asia (Blue Nature vs Stacccato Mix) - Various - February 2005 Part 1 thermodynamic preference for either cyclic or linear hydrogen-bonding motifs. Remarkably, the supramolecular structures formed in solution are preserved upon removal of the solvent, thus yielding predictably organized solid supramolecular architectures. These results demonstrate that control over high-fidelity pathways may substantially impact supramolecular architectures in the solid state, especially upon co-organization with structurally different molecular components for applications in photovoltaic devices.
Furthermore, the melting point m. We thus expected 1 and 2 to self-organize in different supramolecular structures via self-complementary hydrogen bonds.
Because of the absence of reasonable multicomponent self-assembly systems that provide both cyclic and polymeric hydrogen-bonded aggregates soluble without forming higher-order assemblies, the structural preference for these competing hydrogen-bonded motifs have been mainly studied based on solid-state packing structures provided by X-ray crystallography 29 or theoretical approaches Following vapor pressure osmometry VPO 313233 and nuclear magnetic resonance NMR studies of 1 and 2 in chloroform however reveal such a structural preference could occur in equilibrated solution state.
Though the results are indicative of the formation of dimers, the selective formation of dimers was clearly discarded on account of the following concentration-dependent NMR study that illustrate the formation of larger oligomers including cyclic hexamers rosettes. Furthermore, the presence of residual monomers ca. On the contrary, 2 exhibited a linear increase of N with increasing concentration, and N reached 9.
This tractable concentration-dependence of N is in good agreement with the formation of open-ended High Cumberland Jubilee/ Comin Down Slow - Jimmy Buffett - Before The Beach. Concentration-dependent 1 H NMR spectra of CDCl 3 solutions of the regioisomers further demonstrate preferential formation of distinct hydrogen-bonded assemblies Fig.
At submillimolar concentrations, both the regioisomers displayed sharp signals in the range of 7. In contrast, the signals of the aromatic protons H a and H b remained, while broadening, almost constant as a function of increasing concentration, suggesting that 1 forms hydrogen-bonded oligomeric species in CDCl 3.
This finding demonstrates that hydrogen-bonding between 1 molecules occurs with a specific configuration.
This transition could be fitted well using the equal K isodesmic model 35but deviated substantially from both the dimer model 36 as well as the cooperative model 3738 inset, Fig. S13a Compound 2 exhibited a decidedly different behavior in such a concentration-dependent 1 H NMR study Fig.
This trend is very contrastive to that of 1and already at this concentration, different oligomeric species seem to be formed from 2. This change is very contrastive to that observed for 1 Ghettoyouth Arise - LUzine - À La Chaine, and implies that hydrogen-bonding between 2 molecules occurs in non-specific configuration even at this concentration.
These signal patterns unequivocally indicate absence of specific supramolecular species, and reflect the coexistence of diverse polymeric assemblies, the interconversion of which is too slow on the NMR time scale to produce average signals. All of these observations corroborate the formation of open-ended polydispersed polymeric assemblies. S12 at this concentration. Although the exact aggregation number could not be estimated for 1the contrastive DOSY NMR results clearly demonstrate distinct inherent aggregation propensity of the two regioisomers.
Given the contrastive results in the solution-state studies, we attempted to directly visualize hydrogen-bonded aggregates at the liquid—solid interface by means of scanning tunneling microscopy STM.
According to the previous observations 204041our hydrogen-bonded assemblies could be chiral at the solid—liquid interface Excelsior - Olene Kadar - Disco College The formation of two enantiomeric hydrogen-bonded assemblies from achiral components on achiral surface may decrease packing efficiency, which in turn decrease the resolution of the STM imaging. We thus used S - and R -limonene as the chiral liquid phase 4445 in the STM analysis, with the expectation that enantiomerically enriched supramolecular packing through surface confined process Fig.
Concentration of solution is 0. For 1closely packed screw-shaped hexameric rosettes that rotate exclusively clockwise CW or counterclockwise CCW were observed for S - or R -limonene, respectively Fig. In sharp contrast, 2 showed lamellar arrangements of the building blocks Fig. The results of complementary molecular modeling calculations showed that the interlayer spacing L1 4. Thus, 2 exclusively forms infinite hydrogen-bonded tape-like molecular arrays, as observed for a barbituric acid-functionalized merocyanine 47 and a fullerene derivative Hence, it can be concluded that the observed 2D assembly of 1 and 2 is supported by hydrogen-bonding interactions and the two regioisomers favor entirely different hydrogen-bonded molecular arrays not only solution phase but also at the solid—liquid interface.
The preferential formation of the specific hydrogen-bonded motif of 1 and 2 in the 2D-confined space is partially influenced by the kinetic stability of the 2D-packed hydrogen-bonded molecular arrays However, upon considering the obtained VPO and NMR results, it can be concluded that aggregation driven by such specific hydrogen-bonding motif occur under equilibrium conditions as a result of their thermodynamic preference arising from the regioisomerically attached side chains.
Considering these results, we carried out molecular mechanics calculations on the rosettes as well as on monomers 1 and 2 Supprementary Methods. Although the energy minimization did not show an appreciable difference between the stabilization energy of the regioisomers upon rosette formation, we observed a significant structural difference between these rosettes Fig.
In rosettes of 1all hexyl chains are arranged in the rosette plane, whereas in rosettes of 2they are aligned in perpendicular direction with respect to the rosette plane. This structural difference may facilitate van der Waals interactions between neighboring molecules within rosettes and their oligomeric intermediates of 1and thus induce stronger thermodynamic preference toward rosette formation for 1 compared to 2. In the absence of such interactions, the formation of competing tape-like hydrogen-bonded species might prevail as experimentally observed for 2.
The molecular modeled structures are shown in vertical left and perpendicular right direction with respect to the rosette plane. Barbituric acid, oligothiophene, and alkyl chain moieties are colored in light blue, purple, and gray, respectively. The twisting between the barbituric acid, T1and T2 planes in the monomer structures is shown by a schematic cartoon.
The energy minimization of monomeric 1 and 2 furthermore revealed that the specific orientation of the hexyl chains in the rosettes is an intrinsic structural property of the monomers. Hence, it is the twisting between the barbituric acid Total Control - Various - We Are The World T1 that is predominantly responsible for the molecular shape of 2 observed in its rosette architecture.
Accordingly, this subtle conformational difference in the molecular structures, induced by the Help! Asia (Blue Nature vs Stacccato Mix) - Various - February 2005 Part 1 of the side chains, should control the initial self-assembly pathways via directional hydrogen bonds. The bulk sample of 1 showed explicit diffraction peaks with d -spacings which can be assigned to the diffractions from the,,and planes of a 3D lattice Fig.
This structural periodicity might correspond to a helical pitch arising from helical stacking of the rosettes. Values in parenthesis denote Miller indices. In conly left-handed helical columns are used to show the packing structure.
As 1 does not contain a chiral center, both left- and right-handed helical columns should be formed. Help! Asia (Blue Nature vs Stacccato Mix) - Various - February 2005 Part 1 , two sets of diffraction peaks d -spacing of 3. Considering the presence of an additional diffraction peak with a d -spacing of 1. Given that the diffraction peak with a d -spacing of 0. In light of the result from the aforementioned STM study, we would like to propose the following structure for self-organized 2 in the bulk.
The lattice parameter b 1. Conversely, the lattice parameter a 3. Presumably, the supramolecular chains are packed in a slipped brick-like motif, where the oligothiophene units interdigitate each other upon stacking in direction of the c -axis Fig. The distinct self-assembly pathways of 1 and 2 evolving through solvent evaporation were also manifested in a critical difference regarding their bulk-heterojunction BHJ structures with the ball-shaped molecular semiconductor [6,6]-phenyl-C 61 -butyric acid methyl ester PC 61 BM 56 S17abroken curve.
S17asolid curve. The apparent significant discrepancy between the phase transitions of 1 and 1 :PC 61 BM implies that PC 61 BM hampers the self-organization of 1 upon evaporation of the solvent.
We assume that the negligible impact of PC 61 BM on the organization of 2 reflect the occurrence of a macroscopic phase separation due to a morphological mismatch between the assemblies of 2 and PC 61 BM. AFM images of the surface of the thin film of 1 showed particulate nanostructures see Supplementary Fig.
S18ccorresponding to the diffraction from the plane of the rectangular lattice that was observed in the PXRD analysis of the bulk sample of 1 Fig. Thermal annealing merely narrowed the On The Street Where You Live - Ben E.
King - Ben E. King Sings For Soulful Lovers of this diffraction circle. The as-prepared blend film did not show any diffraction circle see Supplementary Fig. S19ccorroborating Follow Me (To Scotland) - Jim MacLeod - Jim MacLeods Family Favourites notion that PC 61 BM hampers the self-organization of 1.
However, the GI-XRD image after the thermal annealing featured a clear diffraction spot with a d -spacing of 2. Thus, the 2D rectangular lattice composed of rosette columns of 1 developed parallelly to the substrate in the presence of PC 61 BM upon thermal annealing, where the a -axis Fig. Combined with the horizontal growth of the nanorods shown by AFM, the elongation of nanorods is driven by the stacking of rosettes along to the c -axis Fig. Average values of four cells with standard deviation.
AFM images of a thin film of 2 showed a pronounced striped texture prior to thermal annealing see Supplementary Fig. The GI-XRD image of the as-prepared film of 2 displayed only a weak diffraction circle with a d -spacing of 3.
Help! Asia (Blue Nature vs Stacccato Mix) - Various - February 2005 Part 1 which should correspond to the diffraction from the plane of the rectangular lattice observed for 2 in the bulk Fig. Consistent with the AFM results, thermal annealing resulted in Help! Asia (Blue Nature vs Stacccato Mix) - Various - February 2005 Part 1 increase of the structural order, as evident from the intensified XRD diffraction posterior to annealing see Supplementary Fig.
This phase-separation feature remained present, even after thermal annealing Fig. As previously discussed, 1 is able to assemble into discrete cyclic rosettes, while 2 tends to form polymeric hydrogen-bonded tapes, which further assemble into an extended 3D structure. We assume that a morphological mismatch between the assemblies of 2 and PC 61 Lolita - Michael Theodore - Ein Lied Geht Um Die Welt might be responsible for the observed macroscopic phase separation, which should render 2 unfavorable for photovoltaic applications.
As 1 and 2 have almost identical optical and electrochemical properties Fig.
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