Self-Assembling Behavior and Chiroptical Properties of Carbazole-Cored Phenyl Isoxazolyl Benzenes

Carbazole-cored phenyl isoxazolyl benzenes possessing chiral moieties were synthesized. The molecules self-assembled to form stacked supramolecular assemblies in an isodesmic fashion in chloroform, whereas the molecules preferably assembled in a cooperative fashion in methylcyclohexane (MCH), which was determined by spectroscopic methods, including UV-vis absorption, fluorescence, and ¹H NMR spectroscopy. Clear nucleation and elongation processes were observed in the plot of the degree of aggregation (α_agg) against temperature, which allowed us to determine the elongation temperature (T_e), the enthalpic gain in the elongation process (ΔH_e), the equilibrium constant between nucleation and elongation (K_a), and the degree of polymerization at the elongation temperature ([N_n(T_e)]). Circular dichroism (CD) and circularly polarized luminescence (CPL) studies revealed the formation of helically stacked assemblies in solution. Moreover, the majority-rule effect was clearly observed in the solutions of mixtures of (S)- and (R)-1, indicating the chiral amplification behavior of the helically stacked assemblies consisting of (S)- and (R)-1. AFM provided morphological insight into the assemblies on mica, which clearly indicates the formation of polymeric assemblies in the solid state.