AlEt3-catalyzed synthesis of circularly polarized luminescence active aggregation-induced emission helical polyisocyanides

Abstract

The facile construction of circularly polarized luminescence (CPL) materials through the clever combination of chirality and fluorescence is of great significance. Herein, we provide a simple and efficient synthesis of CPL-active aggregation-induced emission (AIE) helical polyisocyanides through asymmetric polymerization of commonly used chiral aryl isocyanide monomers featuring a D- or L-methyl-ester pendant group (D/L-IMCIs) catalyzed by a novel AlEt₃/[Ph₃C][B(C₆F₅)₄] binary catalytic system. The typical fluorophore-free chiral D/L-IMCI monomers, silent in circular dichroism (CD), exhibit intriguing AIE properties. After undergoing asymmetric-induced polymerization with remarkable efficiency, the synthesized poly(D/L-IMCI)s have chiral helical structures, manifesting both CD and AIE characteristics. Based on the “matching rule” of the fluorescent moieties and chiral helical polyisocyanides, these poly(D/L-IMCI)s show distinct CPL signals in both the aggregated state and the film state, mirroring each other across the 400–600 nm range in THF, with luminescence dissymmetry factor (|g_lum|) values around 7.6–7.8 × 10⁻⁴ in THF. Moreover, the incorporation of different proportions of an achiral aryl isocyanide bearing an azobenzene pendant (IPPD) into the poly(D/L-IMCI)s through helix-sense-selective copolymerization allows for precise control over the chiroptical properties of the synthesized AIE helical poly(D/L-IMCI-ran-IPPD)s. The nonlinear relationship between the intensity of CD or CPL signals and the D/L-IMCI contents of the synthetic poly(D/L-IMCI-ran-IPPD)s clearly describes strong chiral amplification effects, achieving a maximum |g_lum| value exceeding 1.0 × 10⁻³ in THF, which is superior to those of poly(D/L-IMCI)s. These results demonstrate that the helical (co)polyisocyanide's chirality confers a chiral environment, which in turn effectively induces chirality within both the excited and ground states. This strategy provides new perspectives for the straightforward and simple construction of novel CPL-active AIE polymers through asymmetric polymerization of commonly used functional monomers.