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

Abstract

Mono-and di-quaternized 4,4 -bipyridine derivatives constitute a family of heterocyclic compounds, which in recent years have been employed in numerous applications. These applications correspond to various disciplines of research and technology. In their majority, two key features of these 4,4 -bipyridine-based derivatives are exploited: their redox activity and their electrochromic aptitude. Contemporary materials and compounds encompassing these skeletons as building blocks are often characterized as multifunctional, as their presence often gives rise to interesting phenomena, e.g., various types of chromism. This research trend is acknowledged, and, in this review article, recent examples of multifunctional chromic materials/compounds of this class are presented. Emphasis is placed on solvent-/medium-and environment-responsive 4,4 -bipyridine derivatives. Two important classes of 4,4 -bipyridine-based products with solvatochromic and/or environment-responsive character are reviewed: viologens (i.e., N,N -disubstituted derivatives) and monoquats (i.e., monosubstituted 4,4 -bipyridine derivatives). The multifunctional nature of these derivatives is analyzed and structure-property relations are discussed in connection to the role of these derivatives in various novel applications.Molecules 2020, 25, 1 2 of 30 recent) underlining the high versatility of this class of compounds [9,10,[12][13][14][15]. Perhaps, the most reviewed subject regarding the viologens is their electrochromism [13,14,16]. Viologens are known to undergo one-electron reductions electrochemically ( Figure 2) yielding colorful radicals i.e., cations that are stable in the absence of O 2 . Yet, their chromism can also be triggered through various stimuli (including light, heat, solvents, presence of various chemical species, pressure, etc.). All these possibilities shape the very versatile "chromic character" of viologens and generally of 4,4 -bipyridine derivatives. Even though this "chromic character" has only recently started gaining more attention and there is an increasing number of research articles emphasizing on the alternative uses of 4,4 -bipyridine derivatives, there are no reviews in this growing area up until now. Such an attempt is presented in this review paper with an emphasis on medium-and environment-responsive compounds and materials based on 4,4 -bipyridine. Primary focus is placed on viologen-involving solvatochromic systems as well as materials and compounds of this class whose chromic behavior is dependent on various environment stimuli. Molecules 2018, 23, x 2 of 30 Figure 2. Schemes depicting (a) the electrochromic cycle (1) and (b) the photochromic cycle of paraquat (A, counter anion). Structure and Properties of Viologens The Strong Electron-Withdrawing Character of ViologensThe strong electron-withdrawing character of viologens has been widely exploited in numerous molecular architectures and materials. Viologens can undergo reversible one-electron reductions forming radical cations (Figure 2a), which are vividly colo...

Poly(vinyl pyridine) and Its Quaternized Derivatives: Understanding Their Solvation and Solid State Properties

“…Poly(4-vinylpyridine) (PVP) is a linear polymer with pendant pyridine groups that can be used in a variety of applications, such as surface modification, by immobilizing atoms or particles, electrochemical sensors [ 20 ], fabrication of antibacterial surfaces, development of pH sensitive systems, 3D molecular level ordering systems, anti-corrosive coatings and even dye sensitized solar cells (DSSCs) and light-emitting diodes [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. Positively charged polypyridines constitute a unique class of compounds in which quaternization enables the introduction of permanent positive charges into the backbone, resulting in electron delocalization phenomena that are attributed to the existence of electron-rich pyridines and electron-poor pyridiniums [ 30 , 31 , 32 , 33 ]. As a result, these polymers exhibit improved molecular properties, such as non-linear optical activity and increased conductivity [ 5 , 12 , 18 , 34 , 35 , 36 ].…”

Convenient Access to Functionalized Non-Symmetrical Atropisomeric 4,4′-Bipyridines

“…4,4 -Bipyridines are useful ligands for the design of coordination polymers and metalorganic frameworks (MOFs) [1], and are key components in the preparation of viologens [2,3]. In contrast to 2,2 -bipyridines for which a large number of chiral derivatives were developed [4][5][6], chiral 4,4 -bipyridines were much less explored.…”

Multifunctional Viologen-Derived Supramolecular Network with Photo/Vapochromic and Proton Conduction Properties

“…Crystalline chromic materials have attracted considerable attention for optical memory, visual monitoring, digital anti-counterfeit measures, and environmental detection [ 1 , 2 , 3 ]. Compared to traditional inorganic/organic chromic materials, the introduction of photoelectric organic motifs in crystal engineering is one of the most promising strategies to produce target photochromic materials due to their designable and controllable structures [ 4 , 5 ].…”