Emergence of homochirality in the pathway complexity directed by cosolvent fraction

Probing the phenomenon of homochiral response in supramolecular systems is of significant importance, albeit challenging. The exploration of its underlying mechanism contributes to a deeper comprehension of the natural homochirality phenomenon. Herein, the emergence of homochiral supramolecular assembly is thoroughly investigated and elucidated with the assistance of pathway complexity directed by solvent composition. In a nonaqueous binary solvent environment comprising the cosolvent 1,2-dichloroethane and the “bad” solvent n-hexane, chiral triarylamine tris-amide monomer went through two distinct pathways and the resulting two types of aggregates exhibited entirely different shapes of signals in circular dichroism (CD) spectra. Bisignate Cotton effect was observed in the low cosolvent fraction while monosignate Cotton effect appeared in the high cosolvent fraction case. Two aggregates differed in terms of their morphology, stability, hydrogen bond intensity, macromolecular ordering and internal stacking pattern. The homochiral aggregation was exclusively observed in the high cosolvent fraction environment where R, S and even racemic monomers assembled into aggregates exhibiting identical positive monosignate bands in CD spectra. The emergence of homochiral response is demonstrated to be highly correlated with pathway complexity, and the monomer solubility in two solvents plays a vital role. The concept of relative concentration is introduced to precisely describe the individual solvent effect in a mixed solvent environment. The successful elucidation of homochiral aggregation proves that the binary solvent system constitutes an advantageous platform for investigating and modulating intricate chiral information in supramolecular chiral assembly.