Chiral Binaphthyl[n]arene Gel: Controlled Gelation Ability and Stepwise Amplification of Circularly Polarized Luminescence

Abstract

The construction of circularly polarized luminescence (CPL) materials through self-assembly of chiral macrocycles has garnered significant attention. However, controlling their nanostructure morphology and understanding chirality amplification mechanisms remain challenging. Here, a series of chiral macrocyclic homologs containing varying numbers of binaphthyl units (binaphthyl[n]arene, denoted as n, n = 2–5) are synthesized in a single-step reaction. All macrocycles exhibited CPL, with stronger chiral amplification observed in smaller homologs, 2 and 3, showing dissymmetry factors (|g_lum|) of sixfold and 2.75-fold, respectively, compared to the monomer. These smaller homologs form supramolecular gels in various solvents, while larger ones yield amorphous precipitates. Further enhanced CPL is observed in the gels of 2 and 3, with |g_lum| reaching up to 3.3 × 10⁻³, 8.25-fold and 5.5-fold, respectively, compared to the monomer. While the gel of 3 remained stable for months, the gel of 2 transformed to microcrystals over days driven by π-π interactions. The findings illuminate a macrocyclic strategy to control luminophore arrangement by tuning molecular rigidity and flexibility with macrocycle size, offering a route for creating CPL-active materials with amplified chirality and gels with controlled stability.