Self-assembly of halogen substituted phenazines

Abstract

This paper reports the effect of halogen substituents on the morphology of self-assembling phenazines. Asymmetrically substituted phenazines with decyloxy substituents and halogens (F, Cl, Br, and I) were prepared. Thermal properties were characterized with differential scanning calorimetry (DSC), while polarized optical microscopy (POM) and UV-vis spectroscopy on the cast films of the compounds revealed their assembling ability. A more detailed investigation on the self-assembly was conducted with a phase transfer method. A dramatic morphology difference was observed according to the type of halogen substituents. From F to Cl to Br to I, structures with more one-dimensional (1D) character were produced as confirmed by scanning electron microscopy (SEM). Single crystal X-ray crystallography on Cl substituted phenazine demonstrated hydrogen bonding as the major driving force responsible for the assembly in the longest crystal dimension, while π–π and van der Waals interactions contribute to the growth in the width and thickness directions, respectively. The Br or I substituted phenazines produced assembled structures with more 1D character than either F or Cl substituted phenazines. In addition to the assembly using a phase transfer method, we also present gelation properties for these compounds using select organic solvents.