Control of Kinetic Pathways toward Supramolecular Chiral Polymorphs for Tunable Circularly Polarized Luminescence

An amphiphilic aza‐BODIPY dye (S)‐1 bearing two chiral hydrophilic side chains with S‐stereogenic centers was synthesized. This dye exhibited kinetic‐controlled self‐assembly pathways and supramolecular chiral polymorphism properties in MeOH/H2O (9/1, v/v) mixed solvent. The (S)‐1 monomers first aggregated into a kinetic controlled, off‐pathway species Agg. A, which was spontaneously transformed into an on‐pathway metastable aggregate (Agg. B) and subsequently into the thermodynamic Agg. C. The three aggregate polymorphs of dye (S)‐1 displayed distinct optical properties and nanomorphologies. In particular, chiral J‐aggregation characteristics were observed for both Agg. B and Agg. C, such as Davydov‐split absorption bands (Agg. B), extremely sharp and intense J‐band with large bathochromic shift (Agg. C), non‐diminished fluorescence upon aggregation, as well as strong bisignated Cotton effects. Moreover, the AFM and TEM studies revealed that Agg. A had the morphology of nanoparticle while fibril or rod‐like helical nanostructures with left‐handedness were observed respectively for Agg. B and Agg. C. By controlling the kinetic transformation process from Agg. B to Agg. C, thin films consisting of Agg. B and Agg. C with different ratios were prepared, which displayed tunable CPL with emission maxima at 788 ‐ 805 nm and g–factors between –4.2 × 10–2 and –5.1 × 10–2.