Photochromism, Thermochromism, and Differentiable Amine Detection in a 2D Anionic Cadmium(II) Coordination Polymer with Viologen-Based Guests

High Resolution Image Download MS PowerPoint Slide In this study, a new 2D anionic cadmium(II) coordination polymer with isophthalic acid (H 2 ipa) and 1,1′-dimethyl-(4,4′-bipyridine)-1,1′-diium bromide (Me 2 bipy) formulated as (Me 2 bipy)[Cd 3 (μ 3 -ipa) 2 (μ 4 -ipa) 2 ] n ( 1 ) was synthesized and characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction techniques. The thermal property and phase purity of 1 were investigated by thermal analyses (TG, DTA, and DTG) and powder X-ray diffraction (PXRD) techniques. In 1, the ipa ligand coordinates three- and tetradentate coordination modes. The structure of 1 features a 2D network with a {4 4 .6 2 } point symbol and sql topology, which extends into a 3D supramolecular framework through π···π stacking and C–H···O hydrogen bonding interactions. Host–guest chemistry was employed to incorporate electron-poor viologen guests between the layers of the 2D anionic framework in 1 . Although viologen-containing coordination polymers are often responsive to light, the viologen guests in 1 induce reversible ultrafast photochromism upon UV–vis irradiation. The photochromic behavior results from photoinduced electron transfer to the viologen guest, generating free radicals. These radicals can also be formed by heating compound 1 . At 200 °C, 1 exhibits thermochromic behavior, showing the same color change as observed under UV–vis light. Additionally, compound 1 displays visually detectable, differentiable vapochromic responses to various volatile amines, likely due to electron transfer from the electron-rich amines to the electron-deficient viologen guest.