Photosynthesis is ap rocess wherein the chromophores in plants and bacteria absorb light and convert it into chemical energy.T om imic this process,a ne missive poly(ethylene glycol)-decorated tetragonal prismatic platinum(II) cage was prepared and used as the donor molecule to construct al ight-harvesting system in water.E osin Yw as chosen as the acceptor because of its good spectral overlap with that of the metallacage,w hich is essential for the preparation of lightharvesting systems.S uchacombination showed enhanced catalytic activity in catalyzing the cross-coupling hydrogen evolution reaction, as compared with eosin Yalone.This study offers ap athway for using the output energy from the lightharvesting system to mimic the whole photosynthetic process.Photosynthesis, [1] as the primary source for the fuel on earth, is ap rocess by which living plants and bacteria absorb, capture,t ransfer, and store energy from the sun. In this process,the energy from sunlight is captured and funneled by adense array of chlorophyll molecules to the reaction center, and then converted into chemical energy. [2] So far, many artificial light-harvesting systems mimicking this process have been developed by using aF çster resonance energy-transfer (FRET) process,w ith the aim of developing clean and sustainable energy. [3][4][5] Among them, supramolecular systems [5] have received considerable attention not only because of their tunable and functionable molecular structures but also because the energy transfer between chlorophyll and protein in natural systems also relies on supramolecular selfassembly.F or example,Y ang et al. developed ah ighly efficient light-harvesting system based on the self-assembly of organic nanocrystals. [5b] Wang, Hu, and co-workers reported light-harvesting systems formed by water-soluble pillar[6]arene-based host-guest interactions. [5g] However, most of these systems just mimicked the FRET process of natural systems.T he use of the output energy for photocatalytic reactions has been rarely addressed. As natural photosynthetic systems also use the transferred energy for chemical reactions,artificial light-harvesting systems with the ability to catalyze chemical reactions for storing and releasing chemical energy are urgently needed.Metal-organic cages and metallacages [6] represent threedimensional cagelike structures formed by metal-coordination-driven self-assembly.W ith precisely controlled inner cavities,such fascinating structures have been widely studied in the past three decades for guest encapsulation, catalysis, and stabilizing reactive intermediates,e tc. [7] Recently,S tang et al. developed as eries of emissive metallacages [8] through the incorporation of tetraphenylethylene (TPE) derivatives as the building blocks.T hese metallacages exhibited aggregation-induced emission (AIE) properties [9] because of the restriction of molecular motions that decrease the nonradiative decay.Inartificial light-harvesting systems,thousands of donor molecules are generally used for asingle acceptor,...