Giant Amplification of Fluorescence Quenching in Photochromic Nanoparticles and Crystals

Abstract

Fluorescence photoswitching properties of novel fluorescent photochromic diarylethene (DAE)-benzothiadiazole (BTD) dyads were studied in a solution, in the nanoparticle state, and in the single-crystalline state. The nanoparticles represent a state-of-the-art system, showing bright red emission, reversible fluorescence photoswitching upon UV-visible irradiation, complete ON-OFF contrast, excellent photostability and fatigue resistance. Most interestingly, upon UV irradiation, the nanoparticles exhibit a complete fluorescence quenching even at very low conversion (<5%) of the photochromic unit. This “giant amplification of fluorescence quenching” originates from a long-range intermolecular Forster resonance energy transfer (FRET) within each nanoparticle, leading to the quenching of ~400 fluorescent molecules for only one converted photochromic molecule. Furthermore, similar efficient fluorescence photoswitching was observed even in the single crystal of a DAE-BTD dyad.