Pillar[5]arene derivatives bearing peripheral porphyrin subunits have been efficiently prepared from a deca-azide pillar[5]arene building block (17) and Zn -porphyrin derivatives bearing a terminal alkyne function (9 and 16). For the resulting deca-Zn -porphyrin arrays (18 and 20), variable temperature NMR studies revealed an intramolecular complexation of the peripheral Zn -porphyrin moieties by 1,2,3-triazole subunits. As a result, the molecules adopt a folded conformation. This was further confirmed by UV/Vis spectroscopy and cyclic voltammetry. In addition, we have also demonstrated that the coordination-driven unfolding of 18 and 20 can be controlled by an external chemical stimulus. Specifically, addition of an imidazole derivative (22) to solution of 18 or 20 breaks the intramolecular coordination at the origin of the folding. The resulting molecular motions triggered by the addition of the imidazole ligand mimic the blooming of a flower.
New liquid-crystalline pillar [5]arene derivatives have been prepared by graftingf irst-generation Percectype poly(benzylether) dendrons ontot he macrocyclic scaffold. The molecules adopt ad isc-shaped structure perfectly suited for self-organization into ac olumnar liquidcrystalline phase. In this way,t he pillar [5]arene coresa re piled up, thus forming an anotubular wire encased within as hell of peripheral dendrons.T he capability of pillar [5]arenes to form inclusion complexes has been also exploited. Specifically,d etailed binding studies have been carried out in solution with 1,6-dicyanohexanea st he guest.Inclusion complexes have also been prepared in the solid state. Supramolecular organization into the Col h mesophase has been deduced from X-ray diffraction data and found to be similart ot hat observed within the crystall attice of am odel inclusion complex prepared from 1,4-dimethoxypillar [5]arene and 1,6-dicyanohexane. Pillar[5]arenes are para-cyclophaned erivatives composed of five 1,4-disubstituted hydroquinones ubunits connected by methyleneb ridges in their 2-and 5-positions. [1, 2] Since the first report on their one-step synthesis in 2008b yO goshie tal., [3] pillar [5]arenes have been used for many applications in the field of supramolecular chemistry. [4][5][6][7] Owing to their cylindrical structure, pillar [5]arenes have also been proposed as candidates to generate covalentlyl inked tubulars tructures analogous to carbon nanotubes. [8] In this respect,S toddart and coworkersprepared oligomers by condensationofapillar[5]arene AB monomer.[8] As ar esult of the rigid mode of connection, the oligomeric products resemble tubular nanostructures. [8] Moreover,t he self-assembly of pillar [5]arened erivatives into tubular structures hasa lso been observed in the solid state and in organogels through the occurrence of intermolecular hydrogen-bonding. [9][10][11] As part of this research, we becamei nterested in the preparation of pillar [5]arene derivativesh aving the appropriate shape for the self-organization into columnar liquid-crystalline phases. Whereas supramolecular lamellar organizationsh ave been reported for liquid-crystalline pillar[5]arene derivatives, [12][13][14] the self-organization of pillar[5]arene derivativesi nto tubular nanostructures within ac olumnar phase has, to our knowledge, not been achieved to date. Am ajor problem associated with the design of columnar pillar[5]arene liquid-crystalline derivatives is related to the perpendicular orientation of their aromatic rings with respect to the plane of the macrocycle. Indeed, this orientation prevents the occurrence of intramolecular p-p interactions that could promote self-organization into columns, as observed for macrocyclic systems typicallyu sed for the design of columnar liquid crystals. [15][16][17][18] To solve this problem, the pillar[5]arene core has to be functionalized with peripheral subunitsp rogrammed to promotet heir self-organization into ac olumnar liquid-crystalline materialt hrough appropriate hie...
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