Hydrogen bonds can efficiently guide the self-assembly of organic materials, enabling to tune the properties of the aggregation processes. In the case of p-conjugated materials, several parameters such as temperature, concentration and solvent can be used to modify the aggregation state while tuning the optoelectronic properties. Chirality can be included within the impacting parameters due to the differences in molecular packing. Here, chiral and achiral thiophene-capped diketopyrrolopyrrole derivatives were designed and synthesized containing amide bonds, with the aim to study the interplay between chiral assemblies and their stabilization throughh ydrogen-bonding. Differences in aggregation properties were observed with spectroscopy and microscopy,a nd ac ontactless microwave-based technique was used to study their intrinsic chargec arrierm obility.T he positive role of hydrogen-bonding has been highlighted and the differences between chiral and achiral compoundsh ave been elucidated.
Hydrogen
bonds are noncovalent interactions able to improve the
electronic properties of self-assembled semiconductors. Nevertheless,
it is necessary to control the parameters influencing the formation
of hydrogen bonds to achieve hierarchical structures with enhanced
properties. In this work, we explore two hydrogen-bonded thiophene-capped
diketopyrrolopyrrole (DPP) derivatives containing amides with different
topology (C- or N-centered) and compare them to a control analogue
without hydrogen bonds. We demonstrate the differences in the optoelectronic
and self-assembly properties of the two amide-containing DPP derivatives,
as well as in their charge carrier lifetimes. We prove the superior
properties of the hydrogen-bonded derivatives in comparison to the
control molecule without hydrogen bonds, and show that our molecular
design strategy results in supramolecular structures with particularly
long charge carrier lifetimes compared to other amide-containing semiconductors
reported in the literature.
Some organic compounds are known to self-assemble into nanotubes in solutions, but the packing of the molecules into the walls of the tubes is known only in a very few cases. Herein, we study two compounds forming nanotubes in alkanes. They bear a secondary alkanamide chain linked to a benzoic acid propyl ester (HUB-3) or to a butyl ester (HUB-4). They gel alkanes for concentrations above 0.2 wt.%. The structures of these gels, studied by freeze fracture electron microscopy, exhibit nanotubes: for HUB-3 their external diameters are polydisperse with a mean value of 33.3 nm; for HUB-4, they are less disperse with a mean value of 25.6 nm. The structure of the gel was investigated by small- and wide-angle X-ray scattering. The evolution of the intensities show that the tubes are metastable and transit slowly toward crystals. The intensities of the tubes of HUB-4 feature up to six oscillations. The shape of the intensities proves the tubular structure of the aggregates, and gives a measurement of 20.6 nm for the outer diameters and 11.0 nm for the inner diameters. It also shows that the electron density in the wall of the tubes is heterogeneous and is well described by a model with three layers.
An amide based gelator forms gels in trans-decalin. Below concentrations of 1 wt. % the gels melt at temperatures varying with concentration. Above concentration of 1 wt. %, upon heating,...
The existence of sol–gel transitions is one of the most manifest properties of molecular gels. These transitions reflect their nature since they correspond to the association or dissociation of low weight molecules through non-covalent interactions to form the network constitutive of the gel. Most described molecular gels undergo only one gel-to-sol transition upon heating, and the reverse sol-to-gel transition upon cooling. It has been long observed that different conditions of formation could lead to gels with different morphologies, and that gels can undergo a transition from gel to crystals. However, more recent publications report molecular gels which exhibit additional transitions, for instance gel-to-gel transitions. This review surveys the molecular gels for which, in addition to sol–gel transitions, transitions of different nature have been reported: gel-to-gel transitions, gel-to-crystal transition, liquid–liquid phase separations, eutectic transformations, and synereses.
The phase diagrams of organogels are necessary for applications and fundamental aspects, for instance to understand their thermodynamics. Differential scanning calorimetry is one of the techniques implemented to map these diagrams. The thermograms of organogels upon heating show broad endotherms, increasing gradually to a maximum, at a temperature Tmax, and decreasing back to the baseline, sometimes 10 °C above. This broadening can lead to uncertainty in determining the molar enthalpies and the melting temperatures Tm of the gels. Herein, we have measured the thermograms of the 12-hydroxystearic acid/nitrobenzene gels for weight fractions ranging from 0.0015 to 0.04. Compared with transition temperatures measured by other techniques, the inflection points of the thermograms provide a measurement of Tm with less bias than Tmax. The phase diagram explains why the molar melting enthalpies derived from the thermograms for samples of low concentration are lower than expected. The shapes of the heat flows below the peak correlate quantitatively with the diagrams: after suitable correction and normalization, the integral curves superimpose with the phase diagram in their ascending branch and reach a plateau when the gel is fully melted. The shape of the thermograms upon cooling is also qualitatively explained within the frame of the diagrams.
Hydrogen bonds are noncovalent interactions able to improve the electronic properties of self-assembled semiconductors. Nevertheless, it is necessary to control the parameters influencing the formation of hydrogen bonds to achieve hierarchical structures with enhanced properties. In this work, we explore the impact of amide topology (C- or N-centered) in hydrogen-bonded thiophene-capped diketopyrrolopyrrole (DPP) derivatives, and compare them to a control analogue without hydrogen bonds. We demonstrate the differences in the optoelectronic and self-assembly properties of the two amide-containing DPP derivatives, as well as in their charge carrier lifetimes. We prove the superior properties of the hydrogen-bonded derivatives in comparison to the control molecule without hydrogen bonds, and show that our molecular design strategy results in supramolecular structures with particularly long charge carrier lifetime compared to other amide-containing semiconductors reported in literature.
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