Chiral Copper Clusters as Artificial Light-Harvesting Antennas Enabling Sequential Circularly Polarized Förster Resonance Energy Transfer

Abstract

CCS Chemistry, Ahead of Print.
The continuous transmission and amplification of chirality is a fascinating feature in natural biological systems. However, achieving sequential transmission of circularly polarized luminescence (CPL) through multistep energy transfer remains a formidable challenge. Here, chiral N-heterocyclic carbene-protected Cu3 clusters (R/S-Cu3) were synthesized as light-harvesting antennas, self-assembling into blue-emitting nanospheres with considerable CPL-active. Coumarin 6 (C-6), a green emitter, was introduced as the key relay baton for both chirality and energy transmission. We constructed chiral light-harvesting systems (LHSs) through the coassembly of R/S-Cu3, C-6, and red-emitting Nile Red (NiR), enabling efficient two-step energy transfer with a maximum efficiency (ΦET, max) of 87.86%. Supramolecular engineering was employed to fabricate nanofiber bundles serving as film templates, which facilitated sequential CPL transmission from Cu3 to C-6 and subsequently to NiR. The sequential circularly polarized Förster resonance energy transfer (CP-FRET) was verified via CPL spectral comparisons, resulting in distinct amplification of the dissymmetry factor. This work develops metal cluster-driven sequential CPL and energy transmission in chiral LHSs and provides in-depth insights into CP-FRET mechanism.