Programmed Hyperhelical Supramolecular Assembly of Nickel Phthalocyanine Bearing Enantiopure 1-(p-Tolyl)ethylaminocarbonyl Groups

Abstract

The present paper reports uniqueness of a simple, programmed design of disk-shaped homochiral nickel phthalocyanine (Pc) molecules bearing four enantiomerically pure 1-(p-tolyl)ethylaminocarbonyl groups at their peripheral positions, (Pc-(R) and Pc-(S)), and their controlled self-organization into mesoscopic supramolecular helical fibers with a preferential handedness in solution and onto solid surfaces. A combination of four fundamental intermolecular interactions, including quadruple hydrogen bonding, pi-pi stacking, homochiral interactions of the enantiopure bulky aralkyl entities, and noncoordinating nature of nickel ion of the Pc molecules afforded a high thermal stability of the Pc self-assembly in chloroform (CHCl(3)), tetrahydrofuran, and o-dichlorobenzene and onto hydrophilic mica and hydrophobic HOPG surfaces. A higher-ordered helical self-assembly of Pc disks was observed in these solutions (approximately 200 Pc molecules), while the self-assembly was completely dissociated into monomeric species in N,N-dimethylformamide due to a loss of hydrogen-bonding interactions between Pc molecules. Supramolecular chirality in the hierarchical self-assembly of Pc molecules originated from the presence of (R)- or (S)-chiral centers in the peripheral tails, which rotate noncovalently linked molecular building blocks to effectively form the helical architectures. The helical Pc nanofibers dissolved in CHCl(3), estimated to be ca. 70 nm from peak molecular weight obtained by SEC analysis, acts as a building block for higher-order helical fibers (ca. 1 microm) at single molecular level on the solid surfaces, as demonstrated by the dynamic force mode atomic force microscopy. Regardless of hydrophilic and hydrophobic substrates, the interaction between these Pc molecules and the solid surfaces could not affect the morphology of helical assemblies, indicating a unique robustness of these assemblies.