Switchable near-infrared photoluminescence of PbS quantum dots through light and heat modulated hole transfer to spiropyran molecules

Precise modulation of photoluminescence (PL) of nanomaterials by external control is of great interest in such diverse areas as photocatalysis, memory and sensing. Recent studies have combined colloidal quantum dots (QDs) with photochromic molecules to construct optically switchable PL systems. However, it still remains challenging to switch the PL on and off in the near-infrared (NIR) region with multi-stimuli such as light and heat. Here, we present light and heat triggered modulation of the NIR PL of PbS QDs using adjacent spiropyran derivatives. The NIR PL of PbS was reversibly switched on and off through the isomerization process of spiropyran molecules that can be triggered by either light irradiation or heating. The PL intensity of the off state is low enough to yield an on/off ratio as high as 54. Transient absorption measurements revealed ultrafast photoinduced hole transfer from PbS to spiropyran, the rate and efficiency of which depend critically on the driving force that can be deeply modulated through spiropyran isomerization. This study not only establishes a novel multi-stimuli switchable PL system in the NIR, but also provides fundamental guidelines for the design for such systems for a variety of emerging applications.