Helical Nanostructures of an Optically Active Metal‐Free Porphyrin with Four Optically Active Binaphthyl Moieties: Effect of Metal–Ligand Coordination on the Morphology

Abstract

AbstractAn optically active metal‐free porphyrin (1) with four chiral binaphthyl units attached at the meso‐phenyl substituents through crown ether moieties has been designed, synthesized, and characterized. Its self‐assembly behavior in the absence and presence of K+ was comparatively investigated by electronic absorption and circular dichroism (CD) spectra, transmission electron microscopy (TEM), scanning electron microscopy (SEM), atom force microscopy (AFM), and energy‐dispersive X‐ray (EDX) spectroscopy. In the absence of K+, metal‐free porphyrin self‐assembles into nanoparticles depending mainly on the van der Waals interaction among neighboring metal‐free molecules. In the presence of K+, additionally formed metal–ligand K–Ocrown coordination bonds between K+ and crown units of (R)‐ and (S)‐1 molecules, together with chiral discrimination of chiral side chains and intermolecular van der Waals interactions, induce a right‐handed and left‐handed helical arrangement in a stack of (R)‐ and (S)‐1 molecules, respectively, with an ordered “head‐to‐tail” internal molecular arrangement. This then further hierarchically self‐assembles into highly ordered fibrous nanostructures with a helicity opposite to that of the original porphyrin stack. This clearly reveals the effect of the metal–ligand coordination bonding interaction on the morphology and handedness of self‐assembled nanostructures.