David Reger

The underrepresented class of tetraaryltetrabenzoporphyrins (TATBPs) is investigated thoroughly by DFT calculations, X‐ray diffraction, optical spectroscopy, electro‐ and photochemical studies. Fundamental and unexpected insights were gained about structural and electronic properties of this compound class, which will advance the research around TATPBs based technologies, such as in materials and life sciences.

Abstract

Tetraaryltetrabenzoporphyrins (TATBPs) show, due to their optoelectronic properties, rising potential as dyes in various fields of physical and biomedical sciences. However, unlike in the case of porphyrins, the potential structural diversity of TATBPs has been explored only to little extent, owed mainly to synthetic hurdles. Herein, we prepared a comprehensive library of 30 TATBPs and investigated their fundamental properties. We elucidated structural properties by X‐ray crystallography and found explanations for physical properties such as solubility. Fundamental electronic aspects were studied by optical spectroscopy as well as by electrochemistry and brought in context to the stability of the molecules. Finally, we were able to develop a universal synthetic protocol, utilizing a readily established isoindole synthon, which gives TATBPs in high yields, regardless of the nature of the used arylaldehyde and without meticulous chromatographic purifications steps. This work serves as point of orientation for scientists, that aim to utilize these molecules in materials, nanotechnological, and biomedical applications.

He loves me… he loves me not: In the cover image, porphyrin‐hexaphenylbenzenes are drawn as daisies, that are used to play the game “he loves me … he loves me not”. These multiple‐porphyrin substituted hexaphenylbenzenes were used as precursors for the preparation of the respective hexabenzocoronene derivatives, for example the flower with orange petals. Given that the transformation, commonly known as Scholl reaction, did not always work well, the game “Scholl loves me … Scholl loves me not” is shown in the cover image. More information can be found in the Full Paper by N. Jux et al. on https://doi.org/10.1002/chem.201903113page 15083.

Hexabenzocoronenes (HBCs), functionalized with up to six porphyrins, were prepared and studied. UV/Vis absorption spectroscopy showed variations in the spectral characteristics depending on the number of porphyrins as well as their respective substitution pattern. Insight into solid‐state behavior was obtained by X‐ray crystal structures.

Abstract

Porphyrin–hexabenzocoronene architectures serve as good model compounds to study light‐harvesting systems. Herein, the synthesis of porphyrin functionalized hexa‐peri‐hexabenzocoronenes (HBCs), in which one or more porphyrins are covalently linked to a central HBC core, is presented. A series of hexaphenylbenzenes (HPBs) was prepared and reacted under oxidative coupling conditions. The transformation to the respective HBC derivatives worked well with mono‐ and tri‐porphyrin‐substituted HPBs. However, if more porphyrins are attached to the HPB core, Scholl oxidations are hampered or completely suppressed. Hence, a change of the synthetic strategy was necessary to first preform the HBC core, followed by the introduction of the porphyrins. All products were fully characterized, including, if possible, single‐crystal XRD. UV/Vis absorption spectra of porphyrin‐HBCs showed, depending on the number of porphyrins as well as with respect to the substitution pattern, variations in their spectral features with strong distortions of the porphyrins’ B‐band.

Snowball effect: The rolling‐up of nanographenes by cyclodehydrofluorination on alumina resembles a snowball rolling down a slope. As the snowball accelerates and becomes bigger after each turn, the polycyclic aromatic hydrocarbon (PAH) core becomes more prone to undergo indenoannulation as its size grows after each cyclization. In contrast to the vast majority of reactions dealing with strain energies inherent to synthesis of non‐alternant PAHs, alumina‐mediated C−F bond activation turns out to be more sensitive to electronic effects rather than steric. This fact opens up new possibilities for effective synthesis of non‐alternant nanographenes. The artwork was created by the artist Polina Amsharov specially for this publication (material: acryl, software: Pixelmator). More information can be found in the Communication by K. Amsharov et al. on https://doi.org/10.1002/chem.201902586page 11609.

A hydrogel resembling a Rubik's Cube, a trademark of Rubik's Brand Limited, is made via controllable dynamic covalent interactions. Its layers can be rotated either horizontally or vertically to produce new patterns. Ex situ modification or a chemical stimulus can also produce new color arrangements. The creation of multiple patterns may allow for potential applications in patterns‐related material research.

Abstract

The dynamic behavior of a macroscopic adhered hydrogel stabilized through controllable dynamic covalent interactions is reported. These interactions, involving the cross‐linked formation of a hydrogel through reaction of a diacylhydrazine precursor with a tetraformyl partner, increase as a function of time. By using a contact time of 24 h and different compounds with recognized aggregation‐induced emission features (AIEgens), it proves possible to create six laminated acylhydrazone hydrogels displaying different fluorescent colors. Blocks of these hydrogels are then adhered into a structure resembling a Rubik's Cube, a trademark of Rubik's Brand Limited, (RC) and allowed to anneal for 1 h. This produces a 3 × 3 × 3 block (RC) wherein the individual fluorescent gel blocks are loosely adhered to one another. As a consequence, the 1 × 3 × 3 layers making up the RC can be rotated either horizontally or vertically to produce new patterns. Ex situ modification of the RC or application of a chemical stimulus can be used to produce new color arrangements. The present RC structure highlights how the temporal features, strong versus weak adhesion, may be exploited to create smart macroscopic structures.

The molecular structure of Ho₃N@C ₂ (22010)‐C₇₈ is shown in the cover artwork, along with the two molecules of nickel octaethylporphyrin (Ni(OEP) that surround it in the co‐crystal, Ho₃N@C ₂(22010)‐C₇₈ ⋅2 Ni(OEP)⋅2 toluene. Ho₃N@C ₂(22010)‐C₇₈ contains a planar Ho₃N unit surrounded by a chiral carbon cage. That cage violates the isolated pentagon rule by having two sites where two pentagons share a common edge. Color code: nitrogen, blue; holmium, orange; nickel, green; carbon, gray. More information can be found in the Full Paper by S. Stevenson, H. C. Dorn, M. M. Olmstead, A. L. Balch, et al. on https://doi.org/10.1002/chem.201902559page 12545.

New additions to the family: Insights into the reductive functionalization of fullerenes and its application for preparing highly sophisticated fullerene architectures including an unprecedented 1,4‐cycloadduct are presented. Investigations on the exohedral reactivity of fullerenides and the scope of different electrophiles as addition partners leading to a series of fullerene adducts and cycloadducts involving either 1,2‐ or 1,4‐addition patterns are reported.

Abstract

A systematic screening study of the exohedral reactivity of the reduced fullerenes (fullerenides) C₆₀ ²⁻ and C₆₀ ^⋅− is reported. These doubly and singly negatively charged carbon cages were prepared by two‐fold reduction of C₆₀ with potassium, leading to K₂C₆₀, or by in situ monoreduction with the radical anion of benzonitrile PhCN^⋅−, respectively. Several series of electrophiles, including geminal and distant dihalides, benzyl bromides, and diazonium compounds, were employed as addition partners. In general, the investigated bromides proved to be the most suitable reaction partners. A series of fullerene adducts and cycloadducts involving either 1,2‐ or 1,4‐addition patterns, depending on the precise architecture and the steric demand of the addends, were synthesized and fully characterized. Some of the reaction products are unprecedented and inaccessible forms of neutral C₆₀. The fullerenide chemistry presented here closely resembles related reactions of graphenides and carbon nanotubides, which are the most powerful methods for the functionalization of these macromolecular forms of synthetic carbon allotropes (SCAs). Activation of C₆₀ by negative charging represents a little explored concept of fullerene chemistry, providing both new insights of fullerene reactivity itself and new types of exohedral derivatives.

The rational synthesis of nanographenes and carbon nanoribbons directly on nonmetallic surfaces has been an elusive goal for a long time. We report that activation of the carbon (C)–fluorine (F) bond is a reliable and versatile tool enabling intramolecular aryl-aryl coupling directly on metal oxide surfaces. A challenging multistep transformation enabled by C–F bond activation led to a dominolike coupling that yielded tailored nanographenes directly on the rutile titania surface. Because of efficient regioselective zipping, we obtained the target nanographenes from flexible precursors. Fluorine positions in the precursor structure unambiguously dictated the running of the "zipping program," resulting in the rolling up of oligophenylene chains. The high efficiency of the hydrogen fluoride zipping makes our approach attractive for the rational synthesis of nanographenes and nanoribbons directly on insulating and semiconducting surfaces.

AI Explained: AIEgens containing a diselenide bond, which could co‐assemble with a prodrug into nanoparticles, are reported. The self‐assembly driving forces were explored by molecular dynamics (MD) simulations. The NPs could be broken in the cancer intracellular environment and could be applied for bioimaging and cancer therapy.

Abstract

A fluorescent, diselenide‐containing 9,10‐distyrylanthracene (DSA) derivative (SeDSA) with aggregation‐induced emission (AIE) characteristic was successfully synthesized and SeDSA nanoparticles (NPs) were prepared through a nanoprecipitation method. SeDSA could coassemble with an antitumor prodrug, diselenide‐containing paclitaxel (SePTX), which could be obtained by precipitation, to form SeDSA‐SePTX Co‐NPs (Co‐NPs). Molecular dynamics (MD) simulations reveal that the driving forces for the self‐assembly behaviors of SeDSA NPs and SePTX NPs are π–π interactions and hydrophobic interactions, respectively, while the driving forces for Co‐NPs include hydrophobic interactions between SeDSA and SePTX, π–π interactions between SeDSA molecules and hydrophobic interactions between SePTX molecules. Meanwhile, Se‐Se bonds play a crucial role in balancing the intramolecular forces. These diselenide‐containing nanoparticles (SeDSA NPs, SePTX NPs and Co‐NPs) exhibit a high stability under physiological conditions and excellent reduction‐sensitivity in the presence of the redox agent glutathione (GSH) because of the selenium‐sulfur exchange reaction between diselenide and GSH. Both SeDSA NPs and Co‐NPs show strong orange fluorescence emissions on the account of the AIE feature of SeDSA and they were easily internalized by HeLa and HepG2 cells. Distinctively, the Co‐NPs combine the advantage of SeDSA and SePTX for cell imaging and antineoplastic activity, and exhibit selectivity of cytotoxicities between neoplasia cells and normal cells. This study highlights the development of diselenide‐containing AIEgens as a unique approach to prepare uniform and stable fluorescent nanoparticles for the application in cell imaging and tumor treatment.

The triply linked porphyrin array (porphyrin tape) and recent additions to the triply linked porphyrinoid family including corrole tape, porphyrin‐hexaphyrin hybrid tape, subporphyrin tape, and porphyrin arch‐tape are highlighted in the graphic. These tape‐like molecules can be regarded as polycyclic aromatic molecules, but their optical and electrochemical properties are particularly fascinating, encouraging the study their structure–property relationships. Not only planar molecules, but also distorted structures have been made owing to the development of new synthetic methods. For a full discussion see the Minireview article by T. Tanaka and A. Osuka on https://doi.org/10.1002/chem.201802810page 17188 ff.

After uptake by cancer cells, [3,3’‐Co(1,2‐closo‐C₂B₉H₁₁)₂] ([COSAN]⁻) distributes between the cell membrane and the nucleus, presenting no relevant cytotoxicity even after prolonged incubation times. The interaction between [COSAN]⁻ and CT‐dsDNA was investigated and a strong interaction and the formation of a nanohybrid CT‐dsDNA‐[COSAN] biomaterial was found. High binding affinity of [COSAN]⁻ to proteins was observed by ¹¹B{¹H}‐NMR; this was confirmed in vivo. Biodistribution studies of Na[COSAN] in normal mice show accumulation mainly in the reticuloendothelial system, including liver, lungs, and spleen. Na[COSAN], which display low toxicity and high uptake by relevant cancer cells, accumulate boron within the nucleus and could act as a suitable compound for further development of boron neutron capture therapy agents. For more details, see the Full Paper by C. Viñas et al. on https://doi.org/10.1002/chem.201803178page 17239 ff.

Stable radicals: (B^III–subporphyrin‐5‐yl)dicyanomethyl radicals were explored as the first subporphyrin‐based stable carbon‐centered radicals. These radicals are fairly stable owing to the effective spin delocalization by the subporphyrin core. They form weak π‐dimers in the solid state but exist as free monomers in solution even at low temperature.

Abstract

Stable B^III‐subporphyrin‐substituted dicyanomethyl radicals were synthesized by S_NAr reaction of meso‐bromo‐ or meso‐chlorosubporphyrins with malononitrile followed by oxidation with PbO₂. Different from previously reported dicyanomethyl radicals that underwent σ‐ or π‐dimer formation both in the solid state and in solutions, subporphyrin‐stabilized dicyanomethyl radicals exist as monomers in solutions even at low temperature. DFT calculations revealed efficient spin delocalization over the entire subporphyrin. In the solid state, these radicals form weak π‐dimers with antiferromagnetic interactions depending on the crystal packing structures.