We report the use of helicene with an intrinsic helical molecular structure to prepare covalent organic cages via imine condensation. The organic cages revealed a [3+2]-type architecture containing a triple-stranded helical structure with three helicene units arranged in a propeller-like fashion with the framework integrally twisted. Such structural chirality was retained upon dissolution in organic solvents, as indicated by a strong diastereotopy effect in proton NMR and unique Cotton effects in circular dichroism spectra. Further study on chiral adsorption showed that the chiral organic cages possess considerable enantioselectivity toward a series of aromatic racemates.

Nanographenes are emerging as a distinctive class of functional materials for electronic and optical devices. It is of remarkable significance to enrich the precise synthetic chemistry for these molecules. Herein, we develop a facile strategy to recompose helicenes into chiral nanographenes through a unique oxidative cyclo-rearrangement reaction. Helicenes with 7~9 ortho-fused aromatic rings are firstly oxidized and cyclized, and subsequently rearranged into nanographenes with an unsymmetrical helicoid shape through sequential 1,2-migrations. Such skeletal reconstruction is virtually driven by the gradual release of the strain of the highly distorted helicene skeleton. Importantly, the chirality of the helicene precursor can be integrally inherited by the resulting nanographene. Thus, a series of chiral nanographenes are prepared from a variety of carbohelicenes and heterohelicenes. Moreover, such cyclo-rearrangement reaction can be sequentially or simultaneously associated with conventional oxidative cyclization reactions to ulteriorly enrich the geometry diversity of nanographenes, aiming at innovative properties.

Symmetry breaking in the self-assembly of achiral constituents is of vital importance for the origin of molecular homochirality and developing advanced chiral materials. Here, we report a unique mode of spontaneous symmetry breaking in the aggregates of aza[4]­helicenes with an achiral vibrating helical conjugated structure. The achiral molecules initially form clustered aggregates with a slight chiral bias of the P and M isomers, and subsequently the chiral imbalance is amplified by the conversion of the P and M conformations to favor a more thermodynamic stable π–π stacking (from PM to PP or MM stacking). The dynamical P/M transformation not only promotes the evolution of optical activity following the initial spontaneous symmetry breaking but also favors the healing of chirality after the majority is eliminated by heating. Notably, the aggregates reveal prominent circularly polarized luminescence with the absolute dissymmetry factor approaching 0.01. This work provides additional insights into the pathway of chiral symmetry breaking and illustrates a unique route to develop optically active materials from achiral helical molecules.

A large number of current chemotherapeutic agents prevent the growth of tumors by inhibiting DNA synthesis of cancer cells. It has been found recently that many planar polycyclic aromatic hydrocarbons (PAHs) derivatives, previously known as carcinogenic, display anticancer activity through DNA cross‐linking. However, the practical use of these PAHs is substantially limited by their low therapeutic efficiency and selectivity toward most tumors. Herein, the anticancer property of a nonplanar PAH named [4]helicenium, which exhibits highly selective cytotoxicity toward liver, lung cancer, and leukemia cells compared with normal cells, is reported. Moreover, [4]helicenium effectively inhibits tumor growth in liver cancer‐bearing mice and shows little side effects in normal mice. RNA sequencing and confirmatory results demonstrate that [4]helicenium induces more DNA damage in tumor cells than in normal cells, resulting in tumor cell cycle arrest and apoptosis increment. This study reveals an unexpected role and molecular mechanism for PAHs in selectively killing tumor cells and provides an effective strategy for precision cancer therapies.

Helicene-AIE conjugates with tailored marriage of helicenes and AIE luminophores show prominent fluorescence in the aggregated state with colour varying from blue to green, quantum yield up to 37.0%, and |glum| value up to 0.015.