Coupling intramolecular singlet fission with quantum dots via triplet energy transfer for enhanced photocatalysis

Harnessing two triplet excitons generated from singlet fission (SF) for efficient photochemical conversion remains a great challenge. As a proof-of-concept, a series of inorganic-organic hybrid materials (QD-TC₂) were developed by anchoring a carboxyl-functionalized tetracene dimer (TC₂COOH) onto lead sulfide quantum dots (PbS QDs) with different sizes. This strategic design enables PbS QDs to harvest effectively both triplet excitons produced through intramolecular SF (iSF), thereby enhancing the superoxide radical (O₂˙^-) yield. Transient absorption spectroscopy demonstrates that high yield and long-lived triplets (Φ_T = 120%, τ_T = 187 µs) are produced from TC₂COOH via iSF, and then these triplets are quantitatively transferred to PbS QDs via triplet energy transfer (TET) with a remarkable efficiency of ∼97%. Moreover, the photon energy transfer efficiency (Φ_PET), which is defined as the total efficiency of transferring the absorbed photon energy by the TC₂COOH ligand to the QDs, reaches up to 116%. Spectrophotometric experiments reveal that this unprecedented TET efficiency significantly boosts the O₂˙^- yield in QD-TC₂ compared to pristine PbS QDs, resulting in an enhanced degradation performance of methyl orange. This work not only provides a new approach for the harvesting and utilization of the two triplets of iSF, but also offers a new perspective on sensitizing QDs using the exciton multiplication effect of SF for photochemical conversion.