Towards 1D supramolecular chiral assemblies based on porphyrin–calixarene complexes†

Abstract

The design of functional chiral nanostructures in aqueous solution represents one of the most exciting challenges in supramolecular chemistry, offering potential applications in catalysis, sensing, and materials science. In this scenario, it has already been shown that the hierarchical step-by-step addition of porphyrins to calix[4]arene aqueous solutions yields porphyrin–calixarene supramolecular complexes with exact and tuneable stoichiometries and defined dimensionality. The present study reports the formation of novel 1D porphyrin–calix[4]arene assemblies, achieved through a hierarchical and stoichiometrically controlled self-assembly process in water using host–guest interactions between the anionic trisulfonated porphyrin, H₂DPPS3, and the cationic bis-calix[4]arene, BC₄. In addition, to obtain chiral 1D noncovalent assemblies, the copper(II) porphyrin, CuDPPS3, and the enantiomerically pure bis-calix[4]arenes, (R,R)- and (S,S)-BC4, were also used in aqueous solution. The stepwise formation of linear noncovalent and chiral assemblies, based on porphyrin–calixarene complexes, was demonstrated by a number of different techniques such as: UV-vis spectroscopy, circular dichroism (CD), resonance light scattering (RLS) and scanning electron microscopy (SEM), revealing precise stoichiometries, sequence, dimensionality and induction of chirality.