Photochromic metal-organic frameworks based on diarylethene: Synthesis, crystal structure and application in coating

Abstract

A new photochromic diarylethene metal-organic framework material (DMOF), [Cd₂(BCM) (4,4′-bipyridine)] (Cd(II)-DMOF), has been synthesized by combining 4,4′-bipyridine and diarylethene H₂BCM (H₂BCM = 1,2-bis [5-carboxyl-2-methyl-3-thienyl]-3,3,4,4,5,5-hexafluorocyclo1-ene) with Cd(II). The Cd(II)-DMOF is a 6-coordinate orthorhombic crystal system with prism lengths of 9.919 Å (a), 23.809 Å (b) and 11.740 Å (c), and belongs to the Pnna space group. Cd(II)-DMOF exhibits significant color change between colorless and blue when alternately irradiated with Vis and UV light, due to the reversible transformation of its open-ring and closed-ring form of structure. The compact structure of Cd(II)-DMOF enables it to seal N₂ in the closed-ring state. However, in the case of the open-ring state of Cd(II)-DMOF with a larger aperture, the N₂ is easy to desorb. Doping coating with Cd(II)-DMOF can modify the color by UV and visible light in a very short time, which will extend the possible range of applications.