A Multistimuli Responsive Crystalline Cd(II)-Viologen Coordination Polymer with Single-Crystal–Single-Crystal Transformation

Abstract

It is necessary to develop stable and fast multistimuli responsive materials due to the growing demand in our daily life. In this work, a new viologen-based Cd-complex (1) exhibits multiple thermochromic and photochromic behaviors through 10 states with 7 colors. For example, it responds to both Cu Kα/Mo Kα X-ray sources and UV dual light quickly with a color change from colorless to dark blue (1X) (Cu Kα/Mo Kα X-ray sources) and cyan (1-UV) (UV light), respectively. Interestingly, it exhibits a three-step coloration phenomenon when heated, which is unprecedented in viologen compounds. Crystal 1 undergoes a color change to pink, blue, and brown under 130, 180, and 240 °C, respectively. In addition, upon fumigation, both 1P and 1Q undergo a decoloration process to colorless (1K) and yellow (1T), respectively. Four more states (1P, 1K, 1T, and 1O) obtained via dehydration–hydration treatment are all photochromic. More importantly, via single-crystal–single-crystal transformation (SC–SC), the photochromic and thermochromic behaviors of 1 were investigated from the molecular level, which is also rather rare for thermochromic species. The detailed electron donor and the pathways for electron transfer were clearly given according to the results of crystal structure. The colorful states upon external stimuli may be attributed to the multiple pathways for electron transfer.

Two multifunctional stimuli-responsive materials with room-temperature phosphorescence and their application in multiple dynamic encryption

“…32,33 In this way, a viologen ligand of 1-(3carboxybenzyl)-4,4 0 -bipyridinium chloride (Hcbbpy) has been selected as the functional organic linker based on the following two considerations: (a) as a member of the viologen family, Hcbbpy is well known in thermochromic and photochromic fields owing to its potential applications as display materials and redox mediators and (b) introducing benzyl groups of Hcbbpy can increase the flexibility of the entire molecular skeleton. 34,35 In addition, the trimesic acid crystal shows organic ultralong room temperature phosphorescence with a lifetime of 0.15 s and a phosphorescence quantum yield of 2.7% at 524 nm. 33,36 It has the potential to realize multifunctional stimuli-responsive materials with tunable RTP phenomena using Hcbbpy and trimesic acid.…”

Solvent-Modulated Self-Assembly of Naphthalenediimide-Based Cd(II) Complexes and the Controllable Photochromism via Conformational Isomerization

“…Also, the different coloration states should be responsible for the concentrations of [NDI] − · radical anions and their subtly different substrates or surroundings (Figures a, S18). More importantly, a reasonable modulation of the ED/EA interfacial contact can extend the exciton absorption into the visible region (forming a distinct CT process), thus promoting the onset of ET and the ultrafast visible light photochromic properties . More specifically, in the presence of Cd­(II) cations, the combination of positional heterogeneous electron-deficient NDI and electron-rich carboxylic acids produces a specific arrangement of EDs/EAs and a distinct CT in the visible region, which can stimulate the onset of ET and confer ultra-fast visible-light photochromic properties.…”

Applications of Viologens in Organic and Inorganic Discoloration Materials

“…(k) The UV‐vis diffuse‐reflectance spectral and the luminescence emission spectral changes after detecting different benzenes [126] . (l) Photographs of the complex 1 [127] . Reprinted with permission from Ref.…”

“…Reprinted with permission from Ref. [118] (Copyright 2018, Royal Society of Chemistry), [122] (Copyright 2019, Royal Society of Chemistry), [123] (Copyright 2017, Royal Society of Chemistry), [126] (Copyright 2021, Royal Society of Chemistry), [127] (Copyright 2021, American Chemical Society).…”

“…At the same year, Zheng's group reported a new viologen based CD complex (1). It is a compound with both photochromic and thermochromic behavior through 10 states of 7 colors [127] . Under different external stimuli, the polychromatic conversion of compound 1 is due to the diversity of electron transfer pathways (Figure 15l).…”