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In addition, the cross-peaks between the protons of the same kind of molecules, particularly PBI 1, appear between HH TOCSY spectra, which confirms that this cross-peak signal arose from the intramolecular (through-bond) correlation.Accordingly, this NMR analysis provided evidence for the evolvement of mixed dye assemblies, that is, contact of π-surfaces between PBI 1 and PBI 2, during the formation process of the nanowires in THF/water mixtures.However, major focus in this field being so far on single-component self-assembly to elucidate structure–property relationships.In contrast, multicomponent assembly is by far less explored, despite its high promises for the construction of novel nanosized composite materials.
(b) Ultraviolet–visible absorption spectra (solid lines) and corresponding fluorescence spectra (dashed lines) of PBI 1 (blue) and PBI 2 (red) in THF; concentration, We have first studied the self-assembly behaviour of the new PBI 2 in aqueous medium and compared it with that of the previously investigated PBI 1. 2 days) dissolution process in water, leading to either one-dimensional (1D) nanorods (at a concentration of .Compared with the PBI 1 aggregates, also quite different fluorescence bands are observed for PBI 2 aggregates (Fig. These features suggest that the core-twisted PBI dyes 2 are only weakly coupled in aggregates, which corroborates our earlier conclusions that the main driving force for self-assembly of core-twisted PBI 2 is the hydrophobic effect whilst additional strong π–π interactions are operative in aggregates of planar PBI 1. 9) revealed that the assemblies of this mixed system in water are quite different from those of the individual components, as the co-assemblies grow along 1D axis into long-range, structurally ordered nanowires.Since both types of aggregates, namely well-dissolved PBI 1 nanorods and suspension-forming PBI 2 nanoworms, respectively, can be generated by the same preparation method, that is, by injection of water to the respective PBI dye monomer solution in THF and subsequent slow removal of THF under ambient conditions, we were able to address the effect of water on the self-assembly of a mixture of both PBI dyes and to elucidate the structural features of the aggregates formed. These nanowires are ultrathin with uniform diameter of 3–4 nm (Fig.However, a stable suspension of aggregates was obtained by adding water to molecularly dissolved PBI 2 in THF and subsequent slow evaporation of THF from the THF/HO solution of PBI 2. (b) TEM image of PBI 2 aggregates in water, [PBI 2]=0.03 m M (0.077 mg ml (see Supplementary Fig. This is reasonable because the bulky bay substituents prevent the π-surfaces in PBI 2 dimer from further stacking interactions as already described in our earlier work on the aggregation of related core-distorted PBIs in organic solvents O mixtures (Supplementary Fig. Driven by the hydrophobic effect, these PBI 2 dimers are then further aggregated into structurally less-defined nanoworms in pure water as revealed by our TEM studies.Very different from the homogeneous and rigid segmented nanorod structures observed for PBI 1 (Fig. The formation of these nanoworm structures is apparently evoked by the twisting of the perylene core of PBI 2, leading to a different and less regular packing arrangement compared with PBI 1 aggregates.) and schematic space-filling models illustrating the self-assembly of PBI 1. The ultraviolet–visible spectrum of PBI 2 in pure water (Fig.
Another reason might be the additional challenges encountered by pathway complexity that arises when the growth of a larger nano- or even micrometre-sized structure operates either under kinetic or thermodynamic control, depending on the experimental conditions.