Design Strategies and Redox-Dependent Applications of Insoluble Viologen-Based Covalent Organic Polymers

Abstract

Dicationic quaternary salts of 4,4′-bipyridine, also referred to as the viologen family, are well-known for their interesting redox chemistry, whereby they can be reversibly reduced into radical cationic and neutral moieties. Because of this ability to switch between different redox states, viologens have frequently been incorporated into covalent organic polymers (COPs) as molecular switches to construct stimuli-responsive materials. Although many viologen-based COPs have been reported, hyper-conjugated insoluble COPs started to emerge fairly recently and have not been comprehensively reviewed. In this review, we investigate the design strategies employed in the synthesis of insoluble viologen-based COPs, which can be broadly classified as those with viologen in the backbone and those with viologen as pendant groups. Chemical reactions used in the synthesis of each category, including Sonogashira-Hagihara cross-coupling, Menshutkin and Zincke reactions, are highlighted. Diverse applications of these COPs are discussed with particular reference to the redox state of viologen in each material. Uses of these materials for gas adsorption, organic and inorganic pollutant removal, catalysis, sensing and film fabrication are explored.

Facile synthesis of crystalline viologen-based porous ionic polymers with hydrogen-bonded water for efficient catalytic CO2 fixation under ambient conditions

“…Meanwhile, the small peaks at 399.3/399.0 eV may be assigned to N atoms of fully reduced neutral viologens or unreacted bipyridines. 22 In the XPS Cl 2p spectrum (Fig. 4H) of VIP-Cl, the peaks appeared at 196.8 eV (2p 3/2 ) and 198.4 eV (2p 1/2 ) are assigned to free Cl À anion.…”

“…Recently, different types of ionic polymers that containing diverse ionic moieties such as imidazolium, [15][16][17][18] pyridinium, [19][20][21] viologen, [22][23][24][25] quaternary phosphonium, [26][27][28] and others, 6,7,[29][30][31] have been reported. Amongst, viologen-based ionic polymers have been regarded to be one type of promising functionalized polymers towards diverse applications, due to their unique properties of adjustable redox states and viologen ionic active sites.…”

“…Amongst, viologen-based ionic polymers have been regarded to be one type of promising functionalized polymers towards diverse applications, due to their unique properties of adjustable redox states and viologen ionic active sites. 22,23 In terms of synthesis, a series of viologen-based ionic polymers have been prepared using various strategies including C-C coupling reactions (e.g., Heck reaction, 32 and Sonogashira coupling reaction 33,34 ), ionothermal trimerization, 35 imine condensation, 36,37 Zincke reaction, [38][39][40][41] and Menshutkin reaction. 11,[42][43][44][45][46][47][48] Through coupling reactions and ionothermal reactions can afford viologen-based porous ionic polymers with high surface areas, these processes are complicated and environmental-unfriendly that require noble-metal catalysts or additives or high reaction temperatures.…”

Remarkably efficient removal of toxic bromate from drinking water with a porphyrin–viologen covalent organic framework

“…S13 †). This can be explained by a partial loss of the cationic character of PV-COF: it is well known that bases reduce viologen units to radical cations, 34 which have a lower affinity for bromate than dicationic viologens.…”

Mono- and Di-Quaternized 4,4′-Bipyridine Derivatives as Key Building Blocks for Medium- and Environment-Responsive Compounds and Materials

“…In recent years, the derivatives of 4,4 -bipyridine have been employed in numerous high-tech applications including molecular motors [2], machines [3,4], and switches [5,6]. 4,4 -Bipyridine is highly abundant in supramolecular chemistry as well, where it mainly serves as an electro-and photo-sensitive building block as well as a bidentate coordinating ligand, very often appearing in covalent organic and metalorganic frameworks (COFs and MOFs, respectively) [7][8][9]. A key characteristic of the derivatives of this important building block is their multifunctionality [10,11].…”