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Lead-halide perovskite quantum dots (QDs) have been intensively studied, owing to their excellent optical properties. Herein, the photoluminescence (PL) emission of perovskite QDs was controlled by coupling them with a polyoxometalate (POM) redox cluster to develop photoswitches that undergo changes in optical properties in response to light stimulus. CsPbBr 3 QDs were coated with a TiO 2 layer, and photoinduced electron transfer (PET) from the TiO 2 /CsPbBr 3 QDs to (Bu 4 N) 4 [W 10 O 32 ] (tetrakis(tetrabutylammonium)decatungstate) under visible-light irradiation was examined. UV−vis absorbance, PL emission, and PL lifetime measurements indicated that efficient PET from the QDs to the POM took place under visible-light irradiation, thereby quenching the PL emission. PET also led to the generation of one-electron reduced POM (POM − ). The PL quenching proceeded via PET from QDs to POM, POM − formation, and PET to POM − . POM − was easily oxidized on exposure to atmospheric oxygen, leading to the restoration of the PL. The PL emission could be repeatedly quenched and restored by visiblelight irradiation and oxygen introduction, respectively. The results demonstrate the promising utility of the QD/POM system as photoswitches that can be used for super-resolution imaging, photomemory, fluorescent patterning, and bioimaging.

Lead halide perovskite quantum dots (QDs) have attracted significant attention because of their excellent optoelectronic properties. In this study, we focused on reversibly modulating the photoluminescence (PL) emission of perovskite QDs using a redox cluster of polyoxometalates (POMs). Three different CsPbBr x I3–x (x = 0, 0.4, and 0.7) QDs of 9.6∼12.8 nm diameter were synthesized, stabilized by TiO2 coating, and coupled with (Bu4N)4[W10O32] (tetra-n-butylammonium decatungstate: TBADT) in organic solution. The TiO2-coated CsPbBr x I3–x (CsPbBr x I3–x @TiO2 core/shell) QDs showed bright PL emissions at 705, 678, and 605 nm, which were efficiently quenched by one-electron-reduced W10O32 5– (POM–) via photoinduced electron transfer (PET). Particularly, the PL emission at 705 nm of CsPbI3@TiO2 QDs was most efficiently quenched by 95% via PET and Förster resonance energy transfer (FRET) because of a large spectral overlap between the QD emission and POM– absorbance. The quenching mechanism was analyzed by steady-state and time-resolved PL measurements. CsPbI3@TiO2 QDs was found to photocatalytically reduce POM to POM– by visible light. The PL emission from CsPbI3@TiO2 QDs was reversibly switched between On and Off states by alternately exposing the QD–POM system to intense visible light (PL quenching via PET and FRET) and reoxidation of POM– in ambient air (PL recovery). The obtained results open the possibility of constructing perovskite QD-based photoswitches for super-resolution imaging, optical data storage, smart display, and bioimaging.

Photoswitchable nanomaterials are key materials in the development of advanced imaging techniques, such as super‐resolution fluorescence microscopy. The combination of perovskite CsPbBr3 nanocrystals (NCs) with bright photoluminescence (PL) emission and diarylethenes (DAEs) with structural changes in response to ultraviolet (UV) and visible light is a promising candidate system. Herein, CsPbBr3 NCs are coupled with photochromic DAE molecules to control the PL emission from the NCs by light stimulation. The PL emission is successfully switched ON and OFF by alternating UV and visible light irradiation. Time‐resolved PL emission studies suggest that Förster resonance energy transfer from CsPbBr3 NCs to the closed‐ring form of DAE occurs after UV irradiation, and the PL emission is quenched. Upon visible‐light irradiation, DAE is converted to the open‐ring isomer, and the PL emission is restored. Femtosecond pump‐probe spectroscopy reveals that light stimulation induces not only energy transfer but also photoinduced electron transfer in the NC‐DAE pair on the picosecond timescale to form DAE radicals. Thus, it is suggested that the holes residing in the NCs react with the NCs, degrading the PL emission. Stable PL switching is realized using 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) as a hole scavenger to avoid the reaction between the holes and NCs.

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