Photoswitchable Dual‐Color Fluorescence With Large Stokes Shift From Dye‐Encapsulated Metal‐Organic Framework for Dynamic Cellular Imaging

Abstract

ABSTRACT Photoswitchable dual‐color fluorescent materials are highly valuable for applications in cellular imaging and super‐resolution microscopy. However, realizing these materials, especially broadening their Stokes shift remains a critical challenge. Herein, a novel strategy for achieving photoswitchable dual‐emission fluorescence with a large Stokes shift is proposed via a cascade energy transfer (ET) process in metal‐organic frameworks (MOFs). By incorporating the photoisomerizable molecule spiropyran as an ET intermediate, and two fluorescent dyes coumarin 153 (Cou153) and methylene blue (MB) within a MOF, rho‐ZMOF, the dual‐color dynamic luminescent material rho‐ZMOF⊃Cou153&SP&MB is achieved. When excited at 400 nm, rho‐ZMOF⊃Cou153&SP&MB exhibits coumarin‐centered green emission at 516 nm and methylene blue‐centered red fluorescence at 700 nm, with a maximum Stokes shift of 300 nm. More importantly, these dual‐color emissions can be reversibly switched on or off upon altering UV‐ and visible‐light irradiation because of the photoswitchable cascade energy transfer from coumarin 153 to methylene blue based on the photochromic transformation of spiropyran. As an example, the potential use of rho‐ZMOF⊃Cou153&SP&MB in high‐resolution and depth‐resolved bioimaging is demonstrated.