New redox systems with three oxidation states are highly sought-after, for example, for redox-flow battery applications, selective reducing agents, or organic electronics. Herein, we describe a straightforward and modular synthesis of a new class of such a three-state redox system based on the intermolecular reaction of a large variety of pyridinium salts with carbenes. These hybrids represent organic (super) electron donors with tailored electrochemical properties and feature three stable oxidation states, which could be fully characterized including by X-ray diffraction. We elaborate which electronic factors either promote attainment of stable radicals through one electron transfer or instead favor 2e − processes. Indeed, based on X-ray data, a verification for a potential compression mechanism is given that originates through a large structural distortion in the first oxidation event. By geometrically locking this hybridization change, a potential expansion can be realized. The new class of stable organic radicals are highly persistent and even moderately stable toward air. Additionally, we demonstrate that our modular synthesis approach is also applicable to remarkably strong multielectron (4e − ) donors by utilizing bridged pyridinium salts. Based on the stability and reversibility of the new redox system, we could demonstrate by charge−discharge experiments the use of the hybrid molecules as novel anolyte materials for nonaqueous redox-flow batteries.

Ortho substituted octaazaperopyrenes (OAPPs) are a new class of functional dyes characterized by their strong electron‐accepting behavior. Herein, the synthesis, as well as the electrochemical and photo physical properties of an OAPP dye, is reported. The OAPP target was prepared via selective nucleophilic substitution at the peri position of a bay chlorinated tetraazaperylene by introduction of four amino‐substituents. The resulting tetraminoperylene was reacted with different acyl chlorides and anhydrides to give the twisted bay chlorinated OAPP derivatives which were isolated in their reduced dihydro‐form. The OAPP target could be obtained via a palladium catalyzed dehalogenation and a subsequent oxidation. The eightfold isosteric [CH→N] replacement within the peropyrene core structure results in a large decrease of the frontier orbital energies, rendering the target compound a potent oxidant while preserving the planarity of the aromatic core. The radical anion was obtained by reduction of the OAPP with KC8 and characterized by EPR spectroscopy. A general discussion of the number and location of [CH→N] replacements in peropyrene structures and their frontier orbital energies is provided.

Octaazaperopyrenedioxides (OAPPDOs) are a new class of fluorescent polycyclic aromatic hydrocarbons based on a tetraazaperylene core that is formally condensed with N‐substituted urea units in the two opposite peri positions. Here, we report the synthesis of series of substituted OAPPDO derivatives with different N‐substitution patterns (H, alkyl, benzyl) in the peri positions, including bay‐chlorinated OAPPDOs. Starting from the latter, a series of bay‐arylated OAPPDOs was synthesized by Suzuki cross coupling, which resulted in the formation of helically chiral OAPPDO derivatives. The electrochemical and photophysical properties were investigated by UV/Vis and fluorescence spectroscopy as well as cyclic voltammetry. The P and M enantiomers of a phenylated OAPPDO were separated by semipreparative HPLC and further analyzed by CD spectroscopy. The frontier orbital energies, the mechanism of the isomerization, the electronic excitation and the CD spectrum (TD‐DFT) were computed and compared to the experimental data. The reversible 1e− oxidation of the OAPPDOs generates the corresponding radical cations, one of which was characterized by EPR spectroscopy. The reversible oxidation process was also systematically investigated by spectro‐electrochemistry.

A one-pot combination of gold catalysis and thermal cyclization provides a fast convergent route to benzo[b]fluorenes.

A revised synthesis of Martin’s phosphino-triols (two derivatives) is reported. Once isolated, these thermally sensitive triols were shown to disassemble selectively via an unexpected P–C bond cleavage reaction. This degradation pathway was effectively suppressed via complexation of Al3+ and Sc3+. In the resulting half-cage complexes, the ligand scaffold is bound to each metal (Al3+ and Sc3+, respectively) via all four donor atoms. So far, this κ4-P,O,O′,O″-coordination mode has not been observed for any other phosphino-triol.