A viologen-based Cd(ii) coordination polymer as a multifunctional platform for photochromism, chemochromism and a broad range of fluorescence pH sensing

Abstract

A multi-responsive Cd(II) coordination polymer (1) has been constructed by introducing a viologen derivative as both framework backbone and ligand side pendant. Notably, compound 1 exhibits intriguing properties, including photochromism,...

Cationic Europium–Organic Framework for Chromatographic Column Separation of Ionic Dyes and Stimuli-Responsive Chromic Properties

“…Furthermore, as evidenced by the solid-state UV–vis spectra, this color change is mainly caused by an increase in absorption intensity between 400 and 800 nm and the appearance of new absorption bands at 590, 655, and 727 nm after exposure to Xe-light (Figure a). These new absorption bands, commonly observed in photoactive viologen-based compounds, suggest the generation of viologen radicals through a photoinduced electron-transfer (PET) process. − Furthermore, the detection of a strong EPR signal with a g value of 1.9983, similar to those reported in viologen-based compounds, also confirms the formation of viologen radicals via the PET process after Xe-light irradiation (Figure b). − …”

“…Furthermore, the detection of EPR signals with g values of 2.0035, 2.0039, 2.0042, 2.0038, 2.0015, 2.0026, and 2.0017, similar to the value of a single electron, confirms the formation of free viologen radicals (Figure S20). In addition, these chromic processes were also monitored using Raman spectra, in which clearly reduced band intensity at 1602 cm –1 and heightened band intensity at 1521 cm –1 were observed (Figure S21), similar to those found in other amine-responsive viologen-based compounds. ,,, These findings indicate that the stretching vibration of the pyridinium ring is significantly influenced by the nucleophilic attack of the electron-rich amine/ammonia on the electron-deficient viologen moiety, facilitating the generation of viologen radicals.…”

Crystal structures and stimuli-responsive properties for three novel D–A type salicylhydrazide–viologen compounds with free radical properties under ambient conditions

“…It has been shown that the stability of radicals can be improved by the introduction of electron groups in viologen compounds. 18–24 This suggests that the introduction of electron-donating groups may be an effective strategy.…”

Photo-, Thermo-, Electrochromic, Erasable Inkless Printing, Ions Detection, and UV Detector Properties of Viologen Compounds Based on Homomolybdate/Keggin POMs

“…Color-changing materials are a new type of functional materials with development potential, which can change color with external stimuli . According to the external stimulus sources, they are mainly divided into thermochromic, photochromic, electrochromic, piezoelectric materials, etc. − In recent years, the development of color-changing materials has been very rapid. Due to their important application value and broad development prospects (applied in multiple fields including industry, textile, military, printing, architecture, and anti-counterfeiting labeling), color-changing materials have become one of the current research hotspots. − Since its first proposal in 1932 (clearly defined as a series of quaternary pyridine salts derived from 4,4′-bipyridine), “viologen” has always been an important component of color-changing materials .…”