Thermochromic, Solvatochromic, and Piezochromic Cd(II) and Zn(II) Coordination Polymers: Detection of Small Molecules by Luminescence Switching from Blue to Green

Two novel Cd(II) and Zn(II) based multichromic coordination polymers (CPs) containing 2,4,5-tri(4-pyridyl)-imidazole, L, with general formulas {[Cd2L4(SO4)(H2O)]·(SO4)·21H2O}n, 1, and {[Zn2L4(SO4)(H2O)2]·2(MeOSO3)·25H2O}n, 2, have been synthesized which consist of two-dimensional layered structures with continuous channels. These CPs are found to exhibit instant and reversible solvatochromic properties via visual color change in the presence of various solvent molecules such as DMF, DMA, CH3CN, CH3COCH3, DMSO, and Et3N as well as quick response for the absorption/detection of small molecules such as formaldehyde and acetaldehyde compared to higher aldehydes. The thermochromic and solvatochromic properties are associated with a color change from blue to green under UV light with significant changes in their emission properties and lifetimes. Further, piezochromic properties are associated with color change from blue to cyan under UV. These materials were also found to exhibit greater preference for adsorption of water vapor (200–300 cc/g) over N2 and CO2 gases and also anionic dye sorption such as Congo red from aqueous solution.