An interesting twist: Expanded porphyrins possess Möbius‐strip‐like structures in the solid state and in solution. The high conformational flexibility of individual groups enables a temperature‐ and ...solvent‐dependent switch between Hückel and Möbius aromaticity. Group 10 metals can serve as clamps to stabilize the twist of the Möbius structure (see picture).
A synthetic route towards a novel hexabenzocoronene‐based helical nanographene motif was developed. A hexaphenylbenzene precursor was therefore designed, which cannot undergo, due to steric ...restrictions, a complete planarization reaction. This precursor was transformed under oxidative cyclodehydrogenation conditions to a π‐extended 5helicene, which was fully characterized including X‐ray diffraction analysis.
A twisted nanographene that is based on the well‐established hexabenzocoronene motif is presented. A 5helical unit was implemented into the nanographene structure with the help of steric repulsive effects. The π‐extended helicene was characterized by UV/Vis absorption and emission spectroscopy as well as X‐ray crystallography.
Single‐molecule electronic components (SMECs) are envisioned as next‐generation building blocks in quantum circuit systems. However, challenges such as the reproducibility of the electrode attachment ...to the individual molecules hamper their fundamental investigation. For our purpose, we introduced quasi optoelectronic electrodes (QOEs) that allow for rapid investigations of the properties and suitability of compounds for molecular electronic devices. In particular, we probed hexa‐peri‐hexabenzocoronene (HBC) as a model system for D6h‐symmetrical nanographenes, with porphyrins as QOEs attached to the periphery. We prepared selectively bis‐porphyrin‐functionalized HBCs with ortho‐, meta‐ and para‐substitution and studied their communication properties, in correlation to the geometrical alignment and size of the system, by electrochemistry and optical spectroscopy. Further insights into structure–property relationships were gained by DFT calculations and X‐ray diffraction analysis.
Clear communication: Hexabenzocoronene was utilized as a model system for nanographenes and probed spectroscopically through peripherally attached porphyrins that served as quasi optical electrodes. Nanographenes functionalized selectively in the ortho‐, meta‐, and para‐positions showed differences in the electronic communication between the porphyrins, which is reflected by a distortion of the B‐band.
A systematic series of superbenzene–porphyrin conjugates was synthesized and characterized. All conjugates show a high degree of cluster formation that correlates to the amount of tert‐butylated ...hexa‐peri‐hexabenzocoronenes (tBuHBCs) attached to the porphyrin's periphery. Determined by mass spectrometry and X‐ray diffraction, van der Waals (vdW) interactions like London dispersions (LD), stemming from solubilizing tert‐butyl groups, were identified to be the major reason for the cluster formation. Cluster sizes comprised of more than twenty molecules with masses up to 70 000 Da were observed, which are rare examples of large architectures based on synthetic functional molecules, assembled by dispersion interactions. Novel strategies towards the design of solution processable functional materials, capable of dynamic transformations based on non‐covalent synthesis can be envisioned.
Superbenzene‐porphyrin conjugates were synthesized that show a high cluster formation ability. The cluster size correlates to the amount of tert‐butylated hexa‐peri‐hexabenzo‐coronenes attached to the porphyrin's periphery. Determined by mass spectrometry and X‐ray diffraction, London dispersion interactions stemming from the tert‐butyl groups were identified to be the major reason for the cluster formation.
Within the last decade, tetraaryltetrabenzoporphyrins (TATBP) have gained rising attention, due to their potential in various fields of material science and medicinal chemistry. However, this class ...of compounds still lacks in structural diversity especially in case of low-symmetrical compounds. Herein, mixed condensations were utilized to generate TATBPs with different substituents either in the meso-positions or the periphery of the macrocycle with total yields of 55-58%. The separation of crude mixtures was achieved by feasible chromatographic purification. The influence of symmetry on the electronic properties of TATBPs was studied by optical spectroscopy, electrochemistry and X-ray diffraction.
A feasible two‐step synthesis and characterization of a full series of hexaarylbenzene (HAB) substituted porphyrins and tetrabenzoporphyrins is presented. Key steps represent the microwave‐assisted ...porphyrin condensation and the statistical Diels–Alder reaction to the desired HAB‐porphyrins. Regarding their applications, they proved to be easily accessible and effective high molecular mass calibrants for (MA)LDI mass spectrometry. The free‐base and zinc(II) porphyrin systems, as well as the respective tetrabenzoporphyrins, demonstrate in solid state experiments strong red‐ and near‐infrared‐light emission and are potentially interesting for the application in “truly organic” light‐emitting devices. Lastly, they represent facile precursors to large polycyclic aromatic hydrocarbon (PAH) substituted porphyrins. We prepared the first tetra‐hexa‐peri‐hexabenzocoronene substituted porphyrin, which represents the largest prepared PAH‐porphyrin conjugate to date.
Hexaarylbenzene (HAB)‐substituted (tetrabenzo)porphyrins were found to have useful properties for various applications, such as calibrants for (MA)LDI instruments, as strong red‐ and near‐ infrared light emitters, and as precursors to large superbenzene‐porphyrin light‐harvesting architectures.
Singular reaction events of small molecules and their dynamics remain a hardly understood territory in chemical sciences since spectroscopy relies on ensemble-averaged data, and microscopic scanning ...probe techniques show snapshots of frozen scenes. Herein, we report on continuous high-resolution transmission electron microscopic video imaging of the electron-beam-induced bottom-up synthesis of fullerene C60 through cyclodehydrogenation of tailor-made truxene derivative 1 (C60H30), which was deposited on graphene as substrate. During the reaction, C60H30 transformed in a multistep process to fullerene C60. Hereby, the precursor, metastable intermediates, and the product were identified by correlations with electron dose-corrected molecular simulations and single-molecule statistical analysis, which were substantiated with extensive density functional theory calculations. Our observations revealed that the initial cyclodehydrogenation pathway leads to thermodynamically favored intermediates through seemingly classical organic reaction mechanisms. However, dynamic interactions of the intermediates with the substrate render graphene as a non-innocent participant in the dehydrogenation process, which leads to a deviation from the classical reaction pathway. Our precise visual comprehension of the dynamic transformation implies that the outcome of electron-beam-initiated reactions can be controlled with careful molecular precursor design, which is important for the development and design of materials by electron beam lithography.
Superbenzene-Porphyrin Conjugates Lungerich, Dominik; Hitzenberger, Jakob F.; Marcia, Mario ...
Angewandte Chemie (International ed.),
November 3, 2014, Letnik:
53, Številka:
45
Journal Article
Recenzirano
A free‐base porphyrin carrying two hexabenzocoronene (HBC) substituents in a trans arrangement and its zinc complex have been prepared. The compounds were characterized extensively and found to form ...tricationic dimers in the gas phase. X‐ray crystallography confirms for the zinc complex a profound π‐stacking of the HBC moieties. In contrast, the free‐base porphyrin incarcerates n‐heptane which essentially prevents π‐stacking. Upon excitation of the HBC substituents, efficient energy transfer to the central porphyrin is observed.
Super size me! The first porphyrin conjugate with two superbenzene units shows properties induced by the superbenzene and porphyrin moieties, but also behavior that differs distinctly from that of the individual buildung blocks. The molecule is characterized by standard spectroscopic methods and modern mass spectrometry, and the first X‐ray structure of such a conjugate is presented.
Fused porphycenes have attracted growing interest in recent years. However, the molecules generated to date suffer from different drawbacks such as multistep syntheses, low yields, and the lack of a ...convenient synthetic strategy. Here, we present our latest results concerning the synthesis of a suitable platform for the generation of large fused porphycenes.
A fused porphycene is generated through a shortened synthetic route. This molecule will serve as a starting point for the synthesis of larger fused porphycenes.
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