C- and S-Shaped Perylene Diimide Heterohelicenes: Modular Synthesis and Spiral-Stair-Like π-Stacking

Enantio- and Diastereoselective Synthesis and Spiral-Stair-Like Single Helix Assembly of Figure-Eight Cyclophenylenes

Helix assemblies of chiral molecules can transfer microscopic unimolecular chirality to macroscopic supramolecular chirality, enhancing various chiral properties. In addition to the commonly observed spiral-column-like helix assembly, a small number of spiral-stair-like helix assemblies have also been reported in aromatic nanocarbons with multiple chirality-related irregularities. However, they require separation of diastereomers and/or enantiomers or do not have stable chirality. Here, we report the enantio- and diastereoselective synthesis of figure-eight [10]cyclophenylenes with stable helical chirality by the rhodium-catalyzed four consecutive intramolecular [2 + 2 + 2] cycloadditions of dodecaynes with two flexible biphenyl units. The chiral figure-eight [10]cyclophenylene with ethyl and methyl side chains exhibits the spiral-stair-like single helix assembly in the crystal due to CH-π and CH-O interactions and good CPL properties in solution. Experimental verification of the enantio- and diastereodetermining steps of four consecutive [2 + 2 + 2] cycloadditions is also reported.

Frustrated π-stacking

The properties of functional materials based on organic π-conjugated systems are governed extensively by intermolecular interactions between π-molecules. To establish clear relationships between supramolecular structures and functional properties, it is essential to attain structurally well-defined π-stacks, particularly in solution, as this enables the collection of valuable spectroscopic data. However, precise control and fine-tuning of π-stacks pose significant challenges due to the weak and bidirectional nature of π-π stacking interactions. This article introduces the concept of "frustrated π-stacking," strategically balancing attractive (π-π interaction) and repulsive (steric hindrance) forces in self-assembly to exert control over the sizes, sequences of π-stacks, and slip-stacked structures. These research efforts contribute to a deeper understanding of the correlation between π-stacks and their properties, thereby providing useful insights for the development of molecular materials with the desired performance.

Peri-Decoration of a Tetraazaperylene with Urea Units: Chiral Octaazaperopyrenedioxides (OAPPDOs) and Their Optical and Chiroptical Properties

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.