Zinc(II)-Organic Framework Films with Thermochromic and Solvatochromic Applications

Multiple-stimuli-responsive photoluminescence films based on a Zn^II -organic framework, {[Zn₂ (Htpim)(3,4-pydc)₂ ]⋅4 DMF⋅4 H₂ O}_n (1, Htpim=2,4,5-tri(4-pyridyl)imidazole, 3,4-H₂ pydc=3,4-pyridinedicarboxylic acid), were fabricated. This compound consisted of a 2D corrugated layer, {Zn(3,4-pydc)}_n , which was further pillared using a Y-shaped pillar N-donor ligand (Htpim) to form a 3D-pillared-layer framework with 1D open channels. The rectangular channels in the as-synthesized compound are fully occupied by guest DMF and H₂ O molecules. The framework exhibits instant and reversible thermochromic properties corresponding to the removal of different H₂ O and DMF guest molecules as temperature increases. The pale-yellow crystal undergoes significant redshifting to a greenish emission centered at 530 nm. Compound 1 also showed remarkable solvatochromic effects in the presence of various organic solvents without affecting its structural integrity. In addition, polycrystalline MOF films were grown on an α-Al₂ O₃ support for switchable and fast-response thermochromic and solvatochromic sensors.