ZnSe/ZnS Core/Shell Quantum Dots as Triplet Sensitizers toward Visible-to-Ultraviolet B Photon Upconversion

Recent years have seen a growing interest in developing heavy-metal-free colloidal quantum dots (QDs), such as InP, Si, and CuInS2, as sensitizers for photochemistry. None of these materials, however, could cover the blue part of the spectrum for applications such as blue-to-ultraviolet photon upconversion that is of particular interest for photocatalysis. Herein we report blue-emitting ZnSe/ZnS core/shell QDs as molecular triplet sensitizers for photon upconversion down to the <320 nm region (ultraviolet-B). The upconversion system consists of carboxylated biphenyl as transmitter ligands for QDs and functionalized naphthalene or biphenyl as annihilators (emitters), with the normalized quantum efficiency reaching 6.2 ± 0.2%. Time-resolved spectroscopy reveals that triplet energy transfer from QDs to biphenyl is mediated by an electron transfer step, highlighting the strong reducing power of the band-edge electrons of ZnSe-related QDs that may play a unique role for photochemical applications.