Isoreticular chemically
stable two-dimensional imine covalent organic
frameworks (COFs), further denoted as DUT-175 and DUT-176, are obtained
in a reaction of 4,4′-bis(9H-carbazol-9-yl)biphenyl
tetraaldehyde with phenyldiamine and benzidine. The crystal structures,
solved and refined from the powder X-ray diffraction data and confirmed
by high-resolution transmission electron microscopy, indicate AA-stacked
layer structures. Both structures feature distorted hexagonal channel
pores, assuring remarkable porosity (S
BET = 1071 m2 g–1 for DUT-175 and S
BET = 1062 m2 g–1 for DUT-176), as confirmed by adsorption of gases and vapors. The
complex conjugated π system of the COFs involves electron-rich
carbazole building units, which in combination with the imine groups
allow reversible pH-dependent protonation of the frameworks, accompanied
by charge transfer and shift of the absorption bands in the UV–vis
spectrum. The sigmoidal shape of the water vapor adsorption and desorption
isotherms with a steep adsorption step at p/p
0 = 0.4–0.6 in combination with excellent
stability over dozens of adsorption and desorption cycles ranks these
COFs among the best materials for indoor humidity control applications.
A new water-soluble pillar[5]arene with an amide fragment and triethylammonium groups was synthesized by our original method of aminolysis of the ester groups. Using UV-spectroscopy, it is shown that cationic pillar[5]arenes are able to selectively form 1 : 1 complexes with some hydrophobic anions: the guests with bulky uncharged or negatively charged substituents hindering entry into the macrocycle cavity. Highly selective binding of the most lipophilic guest, methyl orange dye, in the form of organic anion salts by positively charged water-soluble pillar[5]arenes was detected. In the case of the azo dye the appropriate Kass values were 10-100-fold higher than those calculated for the other sulfonic acid derivatives studied. The 2D NMR NOESY (1)H-(1)H spectroscopy confirms the formation of the inclusion complex: negative charge sulfonate head is outside the cavity of pillar[5]arenes and the hydrophobic fragment of the guest is located in the cavity.
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