Novel Supramolecular Artificial Light-Harvesting Systems Based on AIE-active Macrocycle for Efficient White-Light Photocatalysis in Water.

Constructing supramolecular artificial light-harvesting systems (ALHSs) based on the Förster resonance energy transfer (FRET) mechanism provides an optimal platform for understanding the natural photosynthesis and simulating the natural light-harvesting systems. In the present work, rigid macrocycle K-1 with nonplanar conformation and aggregation-induced emission (AIE) property was selected as an energy donor in ALHS, while the non-cyclic AIEgen K-2 was used for comparative study. In aqueous solution, an efficient one-step energy-transfer process was readily established between blue-emitting K-1 and an acceptor (namely PBTB) with orange fluorescence to afford a high energy-transfer efficiency (ΦET) of up to 82.6% at the optimal donor/acceptor (K-1/PBTB) ratio of 1000:40, while the K-2/PBTB assemblies gave a ΦET of 77.9% under the same conditions. Notably, bright white light emission can be successfully realized with a CIE coordinate of (0.33, 0.34) at the ratio of K-1/PBTB = 200:1 and the ratio of K-2/PBTB = 500:3, respectively. Moreover, the triad FRET system was fabricated through energy transfer from the AIEgens to PBTB, then further transferring the captured energy to the final red-emitting receptor (namely as Z1), achieving an efficient two-step sequential energy transfer. When the ratio of K-1/PBTB/Z1 assemblies reached 1000:40:14, the optimal ΦET was 66.4%, which is higher than that of K-2/PBTB/Z1 assemblies under the same ratio. More importantly, it was found that the ALHS based on macrocycle K-1 showed much higher photocatalytic activity for the cross-dehydrogenative coupling (CDC) reaction with an 87% yield under white-light illumination in water than that of the non-cyclic AIEgen K-2 (35% yield). Therefore, the flexibility of this novel supramolecular strategy renders the macrocyclic AIEgen a promising candidate to construct efficient ALHSs for photocatalysis.