<p>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 (<i>Φ</i>_ET) 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.</p>