Synthesis, crystal structure, photochromic behavior and photomodulated luminescence of a calcium-based coordination polymer constructed from 2,5-thiophenedicarboxylic acid and viologen linker

In this work, the synthesis and structural characterization of one coordination polymer based on 2,5-thiophenedicarboxylic acid (H2tdc) and 1-(4-carboxybenzyl)-4,4′-bipyridinium (bcbpy), namely, {[Ca(tdc)(bcbpy)(H2O)](0.5DMF)}n, has been reported. The compound was well characterized by infrared spectra, powder X-ray diffraction and single crystal X-ray diffraction. X-ray crystallography reveals that central seven-coordinated Ca(II) ions in the compound are bridged by chelating-bridging carboxylate groups of two tdc2– anions to give a 2D layered structure. The bcbpy molecules further modify the two-dimensional structure by coordinating with Ca(II) ions via carboxylate groups at one end. Driven by photo-induced electron transfer under UV light, the compound exhibits reversible photochromic behavior from pale yellow to blue within a short time owing to the presence of electron-deficient viologen moieties. Moreover, the photomodulated luminescence property has been investigated. After 5 min of irradiation, the emission intensity of the compound at 430 nm decreased by 83.2% and the emission could be also recovered to the original state after being kept in the dark for 12 h.