Balakrishna Bugga

The halogen matters: Metalla[2]catenanes have been prepared from dinuclear iridium complexes and anthracene‐bridged dipyridyl ligands. Noncovalent π–π stacking interactions enable the formation of the catenanes, and the substitution pattern of the benzoquinone in the bridging dimetallic building blocks determines the topology of the interlinked metallacycles.

Abstract

A series of molecular metalla[2]catenanes featuring Cp*Ir vertices have been prepared by the template‐free, coordination‐driven self‐assembly of dinuclear iridium acceptors and 1,5‐bis[2‐(4‐pyridyl)ethynyl]anthracene donors. The metalla[2]catenanes were formed by using a strategically selected linker type that is capable of participating in sandwich‐type π–π stacking interactions. In the solid state, the [2]catenanes adopt two different configurations depending on the halogen atoms at the dinuclear metal complex bridge. Altering the solvent or the concentration, as well as the addition of guest molecules, enabled controlled transformations between metalla[2]catenanes and tetranuclear metallarectangles.

Shedding light on G‐protein‐coupled receptor activation: VUF15000 is a photoswitchable histamine H₃ receptor agonist showing full G_i protein activation in both its trans and cis isomer. Moreover, it shows dynamic optical H₃ receptor modulation in electrophysiology experiments. VUF15000 can serve as a valuable photochromic tool compound for unraveling the H₃ receptor signaling cascade with spatiotemporal precision.

Abstract

Spatiotemporal control over biochemical signaling processes involving G protein‐coupled receptors (GPCRs) is highly desired for dissecting their complex intracellular signaling. We developed sixteen photoswitchable ligands for the human histamine H₃ receptor (hH₃R). Upon illumination, key compound 65 decreases its affinity for the hH₃R by 8.5‐fold and its potency in hH₃R‐mediated G_i protein activation by over 20‐fold, with the trans and cis isomer both acting as full agonist. In real‐time two‐electrode voltage clamp experiments in Xenopus oocytes, 65 shows rapid light‐induced modulation of hH₃R activity. Ligand 65 shows good binding selectivity amongst the histamine receptor subfamily and has good photolytic stability. In all, 65 (VUF15000) is the first photoswitchable GPCR agonist confirmed to be modulated through its affinity and potency upon photoswitching while maintaining its intrinsic activity, rendering it a new chemical biology tool for spatiotemporal control of GPCR activation.

Polymer power: Polymer donors have shown remarkable photovoltaic performance in non‐fullerene organic solar cells (OSCs). The molecular design strategies are analyzed in terms of developing suitable polymer donors for non‐fullerene acceptors to further improve the power conversion efficiency (PCE) of non‐fullerene organic solar cells.

Abstract

Over the past few years, non‐fullerene organic solar cells have been a focus of research and their power conversion efficiencies have been improved dramatically from about 6 % to over 14 %. In addition to innovations in non‐fullerene acceptors, the ongoing development of polymer donors has contributed significantly to the rapid progress of non‐fullerene organic solar cell performance. This Minireview highlights the polymer donors that enable high‐performance non‐fullerene organic solar cells. We show the impressive photovoltaic devices results achieved by some of important classes of conjugated polymer systems in non‐fullerene organic solar cells. We discuss the molecular design strategies as far as developing matching polymer donors for non‐fullerene acceptors. We conclude with a brief summary and outlook for advances in donor polymers required for commercialization.

Upon soaking a single crystal composed of crown ether based ion channels and [Ni(dmit)₂]⁻ units in a K⁺‐containing aqueous solution, the Li⁺ ions in the crystal were completely and selectively exchanged with K⁺ ions from the solution while the crystalline state of the material was maintained. The ion exchange induced remarkable changes in the magnetic properties and ionic conductivity.

Abstract

Artificial ion channels are of increasing interest because of potential applications in biomimetics, for example, for realizing selective ion permeability through the transport and/or exchange of selected ions. However, selective ion transport and/or exchange in the crystalline state is rare, and to the best of our knowledge, such a process has not been successfully combined with changes in the physical properties of a material. Herein, by soaking single crystals of Li₂([18]crown‐6)₃[Ni(dmit)₂]₂(H₂O)₄ (1) in an aqueous solution containing K⁺, we succeeded in complete ion exchange of the Li⁺ ions in 1 with K⁺ ions in the solution, while maintaining the crystalline state of the material. This ion exchange with K⁺ was selectively conducted even in mixed solutions containing K⁺ as well as Na⁺/Li⁺. Furthermore, remarkable changes in the physical properties of 1 resulted from the ion exchange. Our finding enables not only the realization of selective ion permeability but also the development of highly sensitive biosensors and futuristic ion exchange agents, for example.

Switch it up: Reversible porosity switching and morphological diversity were investigated for different polymorphic forms of an exceptionally stable imine‐linked porous organic cage (POC), TpOMe‐CDA, upon exposure to N,N‐dimethylformamide (DMF) and chloroform solvents (CHCl₃).

Abstract

Porous solids that can be switched between different forms with distinct physical properties are appealing candidates for separation, catalysis, and host–guest chemistry. In this regard, porous organic cages (POCs) are of profound interest because of their solution‐state accessibility. However, the application of POCs is limited by poor chemical stability. Synthesis of an exceptionally stable imine‐linked (4+6) porous organic cage (TpOMe‐CDA) is reported using 2,4,6‐trimethoxy‐1,3,5‐triformyl benzene (TpOMe) as a precursor aldehyde. Introduction of the ‐OMe functional group to the aldehyde creates significant steric and hydrophobic characteristics in the environment around the imine bonds that protects the cage molecules from hydrolysis in the presence of acids or bases. The electronic effect of the ‐OMe group also plays an important role in enhancing the stability of the reported POCs. As a consequence, TpOMe‐CDA reveals exceptional chemical stability in neutral, acidic and basic conditions, even in 12 m NaOH. Interestingly, TpOMe‐CDA exists in three different porous and non‐porous polymorphic forms (α, β, and γ) with respect to differences in crystallographic packing and the orientation of the flexible methoxy groups. All of the polymorphs retain their crystallinity even after treatment with acids and bases. All the polymorphs of TpOMe‐CDA differ significantly in their properties as well as morphology and could be reversibly switched in the presence of an external stimulus.

Macrocyclic molecules and spherical fullerenes: The ease of formation of “nano‐Saturns” is influenced by several factors involving size and shape fitting, and the strength of attractive interactions. Whereas typical belt‐shaped hosts include a guest via π–π interactions, disk‐shaped hosts do so via CH–π interactions and form supramolecular systems the shapes of which are close to that of the planet Saturn.

Abstract

Saturn‐like systems consisting of nanoscale rings and spheres are fascinating motifs in supramolecular chemistry. Several ring molecules are known to include spherical molecules at the center of the cavity via noncovalent attractive interactions. In this Minireview, we generalize the molecular design, the structural features, and the supramolecular chemistry of such “nano‐Saturns”, which consist of monocyclic rings and fullerene spheres (mainly C₆₀), on the basis of previous experimental and theoretical studies. Ring molecules are classified into three types (loop, belt, and disk) according to their shapes and possible interactions. Whereas typical belt‐shaped rings tend to form tight complexes due to the wide contact area via π–π interactions, flat disk‐shaped rings generally form weak complexes due to the narrow contact area mainly via CH–π interactions. In spite of the small association energies, disk‐shaped rings are attractive because such rings can mimic the planet Saturn precisely as exemplified by an anthracene cyclic hexamer–C₆₀ complex.

Dynamic covalent bonds (DCBs) have received significant interest over the past decade. These are covalent bonds, which are capable of exchanging, or switching between several molecules. Particular focus has recently been on utilizing these DCBs in polymeric materials. Introduction of DCBs into a polymer material provides it with powerful properties including self‐healing ability, shape memory properties, increased toughness, ability to relax stresses as well as to change from one macromolecular architecture to another, among other characteristics. This minireview summarizes commonly used powerful DCBs, focusing on simple and often “click” reactions, and highlights the powerful materials that can result from these bonds. Challenges and potential future developments are also discussed in this minireview.

Highly dispersed: The covalent attachment of cobalt porphyrin onto carbon nanotubes is achieved by a substitution reaction at the metal center. This leads to large improvements in the efficiency of electrochemical CO₂ reduction compared to systems where the compounds are physically mixed.

Abstract

Molecular complexes with inexpensive transition‐metal centers have drawn extensive attention, as they show a high selectivity in the electrochemical conversion of CO₂ to CO. In this work, we propose a new strategy to covalently graft cobalt porphyrin onto the surface of a carbon nanotube by a substitution reaction at the metal center. Material characterization and electrochemical studies reveal that the porphyrin molecules are well dispersed at a high loading of 10 wt. %. As a result, the turnover frequency for CO formation is improved by a factor of three compared to traditional physically‐mixed catalysts with the same cobalt content. This leads to an outstanding overall current density of 25.1 mA cm⁻² and a Faradaic efficiency of 98.3 % at 490 mV overpotential with excellent long‐term stability. This work provides an effective pathway for the improvement of the performance of electrocatalysts that could inspire rational design of molecular catalysts in the future.

Upon soaking a single crystal composed of crown ether based ion channels and [Ni(dmit)₂]⁻ units in a K⁺‐containing aqueous solution, the Li⁺ ions in the crystal were completely and selectively exchanged with K⁺ ions from the solution while the crystalline state of the material was maintained. The ion exchange induced remarkable changes in the magnetic properties and ionic conductivity.

Abstract

Artificial ion channels are of increasing interest because of potential applications in biomimetics, for example, for realizing selective ion permeability through the transport and/or exchange of selected ions. However, selective ion transport and/or exchange in the crystalline state is rare, and to the best of our knowledge, such a process has not been successfully combined with changes in the physical properties of a material. Herein, by soaking single crystals of Li₂([18]crown‐6)₃[Ni(dmit)₂]₂(H₂O)₄ (1) in an aqueous solution containing K⁺, we succeeded in complete ion exchange of the Li⁺ ions in 1 with K⁺ ions in the solution, while maintaining the crystalline state of the material. This ion exchange with K⁺ was selectively conducted even in mixed solutions containing K⁺ as well as Na⁺/Li⁺. Furthermore, remarkable changes in the physical properties of 1 resulted from the ion exchange. Our finding enables not only the realization of selective ion permeability but also the development of highly sensitive biosensors and futuristic ion exchange agents, for example.

On the other hand: When the achiral acceptors thioflavin T (ThT) and acridine orange (AO), with different energy bands, were co‐assembled with the nanotube CG it could transfer its chirality to both of the acceptors to give an enhancement of acceptor circularly polarized luminescence (CPL). The excitation energy could be transferred to ThT but only be sequentially transferred to AO.

Abstract

By constructing a supramolecular light‐harvesting chiral nanotube in the aqueous phase, we demonstrate a cooperative energy and chirality transfer. It was found that a cyanostilbene‐appended glutamate compound (CG) self‐assembled into helical nanotubes exhibiting both supramolecular chirality and circularly polarized luminescence (CPL). When two achiral acceptors, ThT and AO, with different energy bands were co‐assembled with the nanotube, the CG nanotube could transfer its chirality to both of the acceptors. The excitation energy could be transferred to ThT but only be sequentially transferred to AO. During this process, the CPL ascribed to the acceptor could be sequentially amplified. This work provides a new insight into the understanding the cooperative chirality and energy transfer in a chiral supramolecular system, which is similar to the natural light‐harvesting antennas.