Solvent-Induced Amplification of Chiral Superstructures of Carbazole Porphyrins in Dynamic Supramolecular Aggregates

Abstract

Herein, we reported design, synthesis and investigation for supramolecular self-assembly of two types of carbazole porphyrins one with free base carbazole porphyrin (codes as 1), and second one zinc (II) metalated carbazole porphyrin (codes as 2) in the various ratios of chloroform (CHCl3, non-polar) and methanol (MeOH, polar) mixed solvent. Typically, in only chloroform both 1 and 2 produce micro-belt like structures, while increasing polar solvents i.e. 90% MeOH in CHCl3 (v/v, 9:1 ratio), 1 resulted as helical microfibres, however, 2 assembled into twisted helical ribbons, respectively. The solution based solvophobic effect on self-assembly demonstrated by using circular dichroism (CD), UV-Vis and emission spectroscopy. Furthermore, X-ray diffraction was used to confirm amorphous nature of assembly and DFT for computational study used to find energy band gap between carbazole and porphyrin. Importantly, Scanning Electron Microscopy (SEM) was employed to visualise chiral supramolecular superstructures of 1 and 2, respectively. It is clear that growth of chiral superstructures is due to π–π stacking of porphyrin core along with hydrophobic interaction of the ethyl hexyl chain. Thus, it is clear that adjusting the ratio of polar to non-polar solvent, hydrophobic carbazole porphyrins confirmed formation of chiral superstructures.