Efficient Multiexciton Energy Transfer from Quantum Dots to Molecular Triplets

Colloidal quantum dots (QDs) have emerged as a class of important materials for light harvesting and conversion applications. Unlike most molecular systems, each QD can accommodate multiple excitons, but these multiexcitons often decay rapidly through nonradiative Auger recombination, strongly limiting their utilization efficiency. Previous studies have adopted molecular acceptors to extract charges from multiexcitons of QDs, but the resulting charge-separated states are eventually lost via recombination. In recent years, triplet energy transfer from QDs to molecules have been established as an effective means for long-time storage of exciton energy for a variety of photochemical applications. To date, however, multiexciton energy transfer from QDs to molecular triplets has never been demonstrated. Here we report efficient energy transfer from the multiexciton states of Cd, Pb-free ZnSe-based QDs to their surface-anchored aggregation-induced-emission (AIE) molecules achieved through stepwise charge-transfer. The key is to first dissociate multiexcitons through rapid interfacial electron transfer, with a remarkable efficiency of 96% even for the average exciton number per QD (⟨<i>N</i>⟩) as large as 5.2. The subsequent hole transfer step then populates multiple AIE molecules to their triplet states, which are utilized for singlet-oxygen generation and organic photocatalysis. Crucially, both the AIE triplet yield and the singlet-oxygen yield increase almost linearly with ⟨<i>N</i>⟩ until ⟨<i>N</i>⟩ reaches 6, indicating that the triplet energy transfer efficiency of multiexcitons is just as efficient as that of single-excitons.