Hierarchical transfer of chiral information from the molecular to the mesoscopic scale by Langmuir–Blodgett deposition of tetrasteroid-porphyrins

Abstract

Chiral mesoscopic structures were obtained by Langmuir–Blodgett (LB) deposition of two tetrasteroid-porphyrins differing by the number of hydroxy groups functionalizing the steroid rings. The morphology of the porphyrin aggregates was characterized by spectroscopy (UV-Vis absorption, steady-state fluorescence, circular dichroism) and microscopy (fluorescence, scanning electrons, atomic force) techniques. Molecular Mechanics calculations were also carried out to analyze the hierarchical self-assembly process leading to the propagation of the structural properties of the tetrasteroid-porphyrin building blocks to the mesoscopic scale of the imaged chiral architectures. It has been found that, while the transfer of chiral information from the molecular to the nanoscale is determined by the winding of the tetrasteroid chains functionalizing the porphyrin scaffold, the morphology of the mesoscopic aggregates (rods or twisted ribbons) is determined by the amphiphilic (rods) or hydrophobic (ribbons) character of the outer surface of the interacting porphyrin nanostructures.