Tetraphenylethylene tricycle-based sequential light-harvesting system through efficient Förster resonance energy transfer for visible light photocatalysis

Supramolecular assembly based on efficient Förster resonance energy transfer (FRET) provides an optimal framework for the development of substantial artificial light-harvesting systems (LHSs). In this study, a sequential two-step light-harvesting system with FRET process was successfully established in aqueous medium where a specially designed deep blue-emitting indole derivative (PZ) served as an energy donor, a novel green-emitting tetraphenylethylene-based tricycle (TPEM) with aggregation-induced emission (AIE) functioned as a relay acceptor, and Nile red (NIR) was used as the terminal acceptor. Due to good spectral overlap and close proximity between donors and acceptors, the triad system (PZ/TPEM/NIR) could allow for significant energy transfer from PZ to TPEM to NIR with a ratio of 1000:40:30, affording very high energy-transfer efficiencies (ΦET) of 98.59%. By properly optimizing the proportion of PZ/TPEM/NIR, bright white light emission was readily obtained with a CIE coordinate of (0.32, 0.33). Significantly, undesired fluorescence quenching was effectively circumvented in the TPEM-based FRET process. The captured solar energy by PZ/TPEM/NIR assemblies can further photocatalyze the Knoevenagel condensation reaction with a high yield of 95% under visible light in an aqueous medium. Therefore, the tunable feature of the supramolecular strategy renders the AIEgen-based macrocycle a highly promising candidate to construct efficient LHSs for photocatalysis.