DMSO-controlled self-assembly of supramolecular structures of aryl-resorcinarenes

Abstract

Molecular interactions of the chair and crown conformers of tetra(4-hydroxyphenyl)calix[4]resorcinarene and tetra(4-methoxyphenyl)calix[4]resorcinarene with several solvents such as isopropanol, ethanol, methanol, dimethylsulfoxide, acetone and acetonitrile were studied. For this, the calix[4]resorcinarenes were synthesized by direct reaction between resorcinol and the corresponding aromatic aldehyde using HCl as catalyst; the conformers obtained were separated and analyzed via FT-IR, MS and NMR spectroscopies. The results of the UV–Vis study showed that the crown-type conformer of tetra(4-hydroxyphenyl)calix[4]resorcinarene forms aggregates that depend on the solvent, while the chair-type conformer does not exhibit the same behavior. A comparative study of the interactions of the crown and chair conformers of tetra(4-methoxyphenyl)calix[4]resorcinarene in these solvents showed that, as occurred in the case of the chair-type conformer of tetra(4-hydroxyphenyl)calix[4]resorcinarene, the two mentioned conformers do not form molecular aggregates either. These observations suggest that for the formation of these molecular aggregates it is essential that in the crown-type conformation the hydroxyl groups on the lower rim are available. This conclusion was supported by COSY spectrum and the calculation of some geometric parameters of the macrocycle using the Winmostar software. In addition to the above, it was also concluded that the nature of the solvent plays a very relevant role in this process of aggregate formation.