Unconventional Photoswitching Behavior of a Diarylethene‐Perylenediimide Dyad in Nanoparticles Emerging from Multiple Intermolecular Energy Transfer Processes

Abstract Photoswitchable fluorescent systems based on photochromic derivatives have various applications, including high‐resolution imaging and information processing. In this context, a key objective is to control, manipulate, and improve the fluorescence photoswitching of molecular systems. Herein, the intriguing zero‐order photokinetics properties of a photochromic‐fluorescent dyad made of one perylenediimide fluorophore (PDI) and two diarylethene photochromes (DAE) are reported, in the nanoparticles state, resulting from efficient intra‐ and intermolecular energy transfer processes from the PDI to the DAE, well‐rationalized by modified photokinetics equations for photochromism. It allowed the fine‐tuning of the photokinetics, leading to either classical or unconventional behavior, depending on the irradiation wavelength. Fluorescence photoswitching is investigated under a microscope, demonstrating a sigmoidal profile for fluorescence recovery which can be satisfyingly reproduced by a suitable mathematical model that is developed. These findings represent a significant advance in the development of enhanced photoswitchable fluorescent systems, showing high contrast, driven by few photons with tunable switching rates.