Trap-Enabled Long Exciton Lifetime in Low-Toxicity Quantum Dots for Enhanced Photochemistry

Prolonging exciton lifetime in colloidal quantum dots (QDs) is crucial to their photochemical applications. Previously, this was achieved through a mechanism called thermally activated delayed photoluminescence (TADPL) for QDs surface-anchored with molecular triplet energy acceptors, in which the molecular triplets sensitized by QDs can repopulate QD-excitons through thermally activated reverse energy transfer. Here, we demonstrate a novel TADPL mechanism achieved by engineering the surface trap states of QDs. Rapid exciton trapping and thermally activated slow detrapping prolong the exciton lifetime of low-toxicity ZnSe-based QDs from the timescale of ∼10 ns to ∼100 µs. Such a long exciton lifetime allows direct engagement of QDs in diffusion-assisted energy transfer, without needing surface-anchored molecules as triplet transmitters, for solution-phase photochemical applications such as photon upconversion and [2 + 2] cycloaddition. This advantage not only greatly streamlines the design of QD-based photochemical systems but also avoids the reliability issue associated with the anchoring between QDs and molecules, as well as enabling facile tuning of the TADPL wavelength range not limited by the availability of molecular triplet acceptors.