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.

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

Discotic Liquid Crystals.

This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.

Ionic Liquid Crystals: Versatile Materials.

1. Dendrimers and Gene Delivery 5274 2. Surface-Engineered Dendrimers in Gene Delivery 5276 2.1. Lipid-Modified Dendrimers 5276 2.2. Fluorinated Dendrimers 5278 2.3. Amino Acid-Modified Dendrimers 5280 2.4. Saccharide-Modified Dendrimers 5281 2.5. Proteinand Peptide-Modified Dendrimers 5283 2.6. Polymer-Modified Dendrimers 5285 2.7. Nanoparticle-Modified Dendrimers 5285 2.8. Cationic-Moiety-Modified Dendrimers 5287 2.9. Other Ligand-Modified Dendrimers 5289 2.9.1. Hormone-Modified Dendrimers 5289 2.9.2. Folic Acid-Modified Dendrimers 5289 2.9.3. Photosensitizer-Modified Dendrimers 5289 2.9.4. Fluorophore-Modified Dendrimers 5289 2.9.5. Aminoglycoside-Modified Dendrimers 5289 3. Conclusions and Perspectives 5289 Author Information 5289 Corresponding Author 5289 Author Contributions 5289 Notes 5289 Biographies 5290 Acknowledgments 5290 Abbreviations Used 5290 References 5291

Surface-engineered dendrimers in gene delivery.

Bipyridinium derivative-based coordination polymers: From synthesis to materials applications

Fast switching ‘transparent-to-black’ electrochromic devices are currently under investigation as potential candidates in modern applications like e-papers or with additional functionality as ultracompact iris or switchable neutral filter in camera systems. However, recent electrochromic devices show either a lack of contrast or slow response times. To overcome these deficiencies we focus on a careful material composition of the colouring hybrid electrodes in our device. We have established a nanoporous Sb-doped SnO
 $${}_{2}$$
 electrode as supporting electrode for chemisorbed electrochromic tetraphenylbenzidine molecules due to its good conductivity in the redox potential range of the molecule. This hybrid electrode was combined with a modified nanoporous TiO
 $${}_{2}$$
 / viologen electrode to realize a high performance, complementary electrochromic device. Fast switching time constants of 0.5 s and concurrently high change in optical density $$\Delta$$
 OD = 2.04 at 605 nm confirm our successful concept. The achieved colouration efficiency of 440 cm
 $${}^{2}$$
 C
 $${}^{-1}$$
 exceeds every high contrast device presented so far. Electrochromic devices have a range of applications as switchable shutters. Here the authors report a hybrid device that uses complementary electrochromic molecules immobilized on nanoporous electrodes to concurrently achieve fast colouration and bleaching with high contrast over a broad spectral range.

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Complementary hybrid electrodes for high contrast electrochromic devices with fast response.

The present work reports a simple and versatile pathway to incorporate redox-active 4,4′-bipyridinium (“viologen”) units with two, three, or six charges into dynamically ordered liquid crystalline structures by ionic interactions. A detailed analysis of the structure–property relationship was supported by molecular modelling experiments. Three redox-active 4,4′-bipyridinium (“viologen”) cores, 1,1′-dimethyl (4-pyridin-4-ylpyridinium) di- (MV2+2+2+2+), 1,1′,1′′-[benzene-1,3,5-triyltris(methylene)]tris(4-pyridin-4-ylpyridinium) tri- (V3+3+3+3+3+), and 1,1′,1′′-[benzene-1,3,5-triyltris(methylene)]tris[(methyl) 4-pyridin-4-ylpyridinium] hexa- (MV6+6+6+) cationic halides, were combined with an anionic caesium 3,4,5-tris(dodecyloxy)benzene sulfonate (DOBS) under phase transfer conditions to yield complexes of constant stoichiometry. The formed complexes, MV2+2+2+(DOBS)222, V3+3+3+(DOBS)333 and MV6+6+6+(DOBS)666, were characterized by NMR spectroscopy. Depending on the molecular structure, significantly different characteristics in electrochemical behaviour of ionic liquid crystals (ILCs) with two DOBS anions and a rod-like core (MV2+2+2+2+) were observed compared with ILs with three and six DOBS anions and y-shaped cores (V3+3+3+3+3+), and (MV6+6+6+) cations respectively. We report for the first time a new electroactive thermotropic liquid crystal, MV2+2+2+(DOBS)222, which changes colour from yellow to blue-green above 75 °C typically for redox units in the reduced state. The reduced states of the MV2+2+2+(DOBS)222 complex at E = −2 V exhibit reversible redox waves and have influence on molecular arrangement in the crystal structure as seen by polarisation microscopy. Our ionic liquid crystals have potential applications, due to their low melting temperature, wide temperature range, ionic conductivity, and thermal- and electro-chromism, for instance, for the design of electrochromic displays.

Thermotropic ionic liquid crystals by molecular assembly and ion pairing of 4,4′-bipyridinium derivatives and tris(dodecyloxy)benzenesulfonates in a non-polar solvent

http://pubs.acs.org/doi/pdf/10.1021/bc500191q

Examination of structure-activity relationship of viologen-based dendrimers as CXCR4 antagonists and gene carriers.

Chemical and Electrochemical Studies of Carbon Black Surface by Treatment with Ozone and Nitrogen Oxide

The present article deals with novel compounds comprising a redox-active group as core and a nucleobase in the peripheries, linked covalently via a spacer. The new derivatives 1,1′,1″-(benzene-1,3,5-triyltrimethanediyl)tris{1′-[3-(3,4-dihydro-5-methyl-2,4-dioxopyrimidin-1(2H)-yl)propyl]-4,4′-bipyridinium} hexafluorophosphate (1), 1,1′,1″-(benzene-1,3,5-triyltrimethanediyl)tris{1′-[2-(4-chloro-7H-pyrrolo[2,3-d]pyrimidine-7-yl)ethyl]-4,4′-bipyridinium} hexachloride (2a)1 , and 1,1′,1″-(benzene-1,3,5-triyltrimethanediyl)tris{1′-[2-(2-amino-4-chloro-7H-pyrrolo[2,3-d]pyrimidine-7-yl)ethyl]-4,4′-bipyridinium} hexabromide (2b)1) were synthesized by nucleobase-anion alkylation and linked to the 4,4′-bipyridinium core. UV and CV analyses of these compounds were performed and revealed significantly different properties.

Marius Ciobanu

Papers

Complementary hybrid electrodes for high contrast electrochromic devices with fast response.

Thermotropic ionic liquid crystals by molecular assembly and ion pairing of 4,4′-bipyridinium derivatives and tris(dodecyloxy)benzenesulfonates in a non-polar solvent

Examination of structure-activity relationship of viologen-based dendrimers as CXCR4 antagonists and gene carriers.

Chemical and Electrochemical Studies of Carbon Black Surface by Treatment with Ozone and Nitrogen Oxide

Novel Compounds with a Viologen Skeleton and N-Heterocycles on the Peripheries: Electrochemical and Spectroscopic Properties