Direct ¹²⁹Xe-NMR spectroscopy evidence of a mesogenic dendrimer with free void space

Abstract

A dendrimer with 3-fold symmetry and piperazinoamido moieties was prepared in ~35% yield. This molecule was observed to exhibit columnar phases on thermal treatment and possess free void space in...

Shape-Persistent Dendrimers

“…Based on the XRD data, dendrimer 11 , with 2D packing, shows a rectangular columnar phase with the lattice constants of a = 57.5 Å and b = 41.9 Å. As shown in the literature [ 42 ], the dihedral angle of C1-N2-C3-C4 of 11 in the gas phase was calculated to be 25.0 °C, which forces the central core of dendrimer 11 to be non-coplanar, making the inner pore inside the dendritic framework available for guest gases in the mesogenic or solid state. The NMR study revealed that 129 Xe gas can be absorbed into the free void space inside the dendrimer at a temperature range of about −20~80 °C upon heating and at a range of about 105~8–35 °C upon cooling.…”

“…Although dendrimers with rigid linkers and flexible peripheral groups can exhibit a persistent shape, the inner void space inside the dendritic framework is rarely reported to be accessible to external gases in the mesogenic or solid state. Very recently, a dendrimer with a triamidobenzene core, as demonstrated in Figure 6 , was synthesized, and it was observed that it can adsorb Xe gas in the mesogenic and solid states based on a 129 Xe-NMR spectroscopy study at various temperatures [ 42 ]. The related mesogenic ranges are provided in Table S1 .…”

“…The NMR study revealed that 129 Xe gas can be absorbed into the free void space inside the dendrimer at a temperature range of about −20~80 °C upon heating and at a range of about 105~8–35 °C upon cooling. According to the literature [ 42 ], this is the first report demonstrating that a liquid crystalline dendrimer possesses a free void space in the mesogenic and solid states.…”

“…Mesogenic dendrimers with an aromatic core, such as the structures 12 – 14 as cores and linkers, may show good charge mobility in related devices, such as organic field-effect transistors, because of their proper arrangement, which is characterized by a long-range order [ 60 , 61 ]. In particular, one mesogenic dendrimer with shape-persistent morphology has been recently observed to adsorb Xe in the mesogenic and solid states [ 42 ], which may increase the applicability of 2D shape-persistent dendrimers in the area of sensing gases. Due to their good ordering, this kind of dendrimer should show a good gas-detecting ability.…”

Direct evidence of mesogenic dendrons with free void space by Brunauer–Emmett–Teller (BET) isotherms

“…Previously, we first reported an LC dendrimer that self-assembled into columnar stacks and thus possessed free void space for directly adsorbing Xe in the mesogenic or solid state by introducing a non-coplanar unit, the amidopiperazine moiety, on its dendritic frame. 12 Here, using a different strategy for preparing porous LC materials, we further synthesize two CN-containing dendrons with different lengths of central corner, which couple into dendrimer-like molecules via dipole–dipole interaction, thus exhibiting a mesogenic phase upon thermal treatment. Because of the various lengths of central corner, the free void spaces fabricated by two dendrons are different, as determined on the basis of their BET isotherms.…”