Terrylene bisimide-diarylethene photochromic switch

Abstract

A new photochromic system 2o/2c based on a highly photostable terrylene bisimide (TBI) fluorophore and a diarylethene (DAE) photochrome has been synthesised and its photoswitching properties have been investigated by UV/vis absorption and fluorescence spectroscopy and by cyclic voltammetry. Our detailed studies reveal that the fluorescence of this system is photoswitchable by reversible modulation of intramolecular electron transfer (PET). Cyclovoltammetry measurements have shown that the reduction potentials of the open and closed form of the DAE moiety of this photochromic system differ significantly, thus the electron transfer from the excited TBI donor takes places only to the closed form of DAE acceptor. Accordingly, switching between both states of the DAE unit by irradiation with UV and visible light leads to a significant difference in fluorescence quantum yields of TBI unit of open 2o and closed form 2c. The driving force for the emission quenching by PET has been estimated by the Rehm–Weller equation, providing a ΔG° value of −0.24 eV for the closed form, while this value is positive (0.16 eV) for the open form. The photostability of the present system has been proven by repeating switching cycles performed by alternating irradiation with UV and visible light.