White-emitting quantum dots (WQDs) have garnered significant attention due to their substantial application potential in lighting, displays, and visible light communication. Research on the regulation of photoluminescence (PL) switching of WQDs holds promise for advancing technologies in intelligent color displays, efficient lighting, optical information storage, encryption, and smart sensors. Precise on/off control of PL can be achieved by integrating molecular photoswitches with QDs characterized by high luminescence efficiency and stability, and leveraging the property that PL can only be quenched by a specific configuration of the molecular photoswitches. However, traditional F?rster resonance energy transfer (FRET) and photoinduced electron transfer (PET) mechanisms exhibit limitations in regulating the PL switching of WQDs. Therefore, there is an urgent need to develop a novel PL switching scheme for broad-spectrum emitting WQDs. In this study, we develop a PL switching system based on white-emitting ZnCuInGaS@ZnS (ZCGIS@ZnS) QDs and carboxyl-functionalized diarylethene molecular photoswitches (ac-DAE). This system leverages an efficient triplet energy transfer (TET) mechanism between the two components, which offers several advantages over traditional FRET and PET approaches. TET operates by transferring energy from the triplet excited state of the QDs to the triplet state of the photoswitches, which results in the quenching of the PL. Importantly, this mechanism exhibits excellent fatigue resistance, which means that repeated cycles of PL switching do not significantly degrade the performance of the system. We believe that utilizing the TET mechanism to regulate the PL of WQDs will offer extensive potential applications in intelligent color displays, lighting, optical information storage, encryption, and smart sensors.

Broad-spectrum white-light-emitting ZCGIS@ZnS core-shell QDs are synthesized using the hot-injection method. The fundamental PL properties and structure of ZCGIS@ZnS QDs are characterized using ultraviolet-visible (UV-Vis) absorption spectroscopy, PL spectroscopy, PL lifetime, X-ray diffraction, and transmission electron microscope measurements. To construct energy transfer systems, tert-butyl-functionalized diarylethene (t-DAE) and carboxyl-functionalized DAE (ac-DAE) are physically mixed with the ZCGIS@ZnS QDs. Subsequently, the configurational transformation of t-DAE and ac-DAE is selectively controlled using LED light sources with wavelengths of 310 nm and 515 nm, respectively. In-situ UV-Vis absorption spectra and PL emission spectra are recorded to investigate the quenching effects of the two molecular photoswitches on the PL of ZCGIS@ZnS QDs and to elucidate the differences in their respective quenching mechanisms. The proposed energy transfer mechanism is further validated through nanosecond transient absorption spectroscopy. Finally, the fatigue resistance stability of the system is evaluated.

The synthesized ZCGIS@ZnS QDs exhibit broad-spectrum white light emission with a full width at half maximum (FWHM) of 191.5 nm [Fig. 2(a)]. Two types of molecular photoswitches, t-DAE and ac-DAE, are selected for their ability to undergo configurational transitions under light irradiation at 310 nm and 515 nm [Figs. 2(c) and 2(d)]. This enables the ZCGIS@ZnS-DAE system to achieve reversible PL switching at these two wavelengths. In-situ PL intensity measurements reveal that when t-DAE is used to regulate the PL of WQDs, the process dominated by the mechanism of F?rster resonance energy transfer can only quench the PL of WQDs by 34.1%, with a PL on/off ratio of 1.5 [Fig. 3(b)] . When ac-DAE is employed, covalent bonding between the carboxyl groups and the WQDs’ surface facilitates short-range Dexter energy transfer. The PL quenching efficiency and on/off ratio reach as high as 99.2% and 125 in this case [Fig. 3(e)]. Particularly, the Stern-Volmer quenching rate in the ZCGIS@ZnS-ac-DAE system is as high as 5.16×10¹¹ mol^-1·L·s^-1 [Fig. 3(f)] . This value is significantly higher than that of diffusion-limited bimolecular excited-state interactions. The enhanced quenching efficiency can be attributed to the covalent attachment of ac-DAE to the QDs’ surface, which minimizes energy transfer losses. Additionally, the prolonged excited-state exciton lifetime of ZCGIS@ZnS QDs [3.13 μs, Fig. 2(b)] allows sufficient time for efficient energy transfer to ac-DAE, rather than undergoing radiative recombination and luminescence. The emergence of a characteristic triplet absorption peak in the nanosecond transient absorption spectra confirms the TET mechanism based on Dexter energy transfer [Fig. 4(a)]. The system exhibits excellent reversibility and fatigue resistance over 8 switching cycles (Fig. 5). This study demonstrates that utilizing DAE photoswitches achieves efficient and reversible optical modulation of the PL between on and off states of WQDs.

In this study, we employ a novel TET mechanism to achieve efficient PL switching modulation of broad-spectrum white-light-emitting ZCGIS@ZnS QDs using DAE molecular photoswitches. In the ZCGIS@ZnS-ac-DAE system, the PL quenching efficiency reaches 99.2%, with a corresponding PL on/off ratio of 125. Compared to the traditional FRET mechanism, the TET mechanism demonstrates broader applicability in PL modulation. The characteristic triplet absorption signal at 775 nm observed in the nanosecond transient absorption spectra further validates the TET mechanism. The system exhibits excellent reversibility and fatigue resistance over 8 switching cycles. This research indicates that the TET mechanism can be effectively utilized to switch the PL behavior of WQDs, thus offering extensive potential applications in intelligent color displays, lighting systems, optical information storage, encryption technologies, and smart sensors.