Revealing Pathway Complexity and Helical Inversion in Supramolecular Assemblies Through Solvent-Induced Radical Disparities

New insights are raised to interpret pathway complexity in the supramolecular assembly of chiral triarylamine tris-amide (TATA) monomer. In cosolvent systems, the monomer undergoes entirely different assembly processes depending on the chemical feature of the two solvents. Specifically, 1,2-dichloroethane (DCE) and methylcyclohexane (MCH) cosolvent trigger the cooperative growth of monomers with M helical arrangement, and hierarchical thin nanobelts are further formed. But in DCE and hexane (HE) combination, a different pathway occurs where monomers go through isodesmic growth to generate twisted nanofibers with P helical arrangement. Moreover, the two distinct assemblies exhibit opposite excited-state chirality. The driving force for both assemblies is the formation of intermolecular hydrogen bonds between amide moieties. However, the mechanistic investigation indicates that radical and neutral triarylamine species go through distinct assembly phases by changing solvent structures. The neutralization of radicals in MCH plays a critical role in pathway complexity, which significantly impacts the overall supramolecular assembly process, giving rise to inversed supramolecular helicity and distinct morphologies. This differentiation in pathways affected by radicals provides a new approach to manipulate chiral supramolecular assembly process by facile solvent-solute interactions.

Construction of Helical Structures with Multiple Fused Anthracenes: Structures and Properties of Long Expanded Helicenes

Polycyclic aromatic compounds consisting of four or five fused anthracene units were synthesized by PtCl₂ -catalyzed cycloisomerization as novel long expanded helicenes. These compounds have helical structures with significant stacking of the terminal anthracene moieties at 0.33 nm interlayer distance. In the UV-vis and fluorescence spectra, the absorption and emission bands were red-shifted as the number of fused anthracene units was increased. The characteristic broad and long-lived emission bands of the long analogues are explained by the excimer-like stabilization of the excited state. These photophysical data as well as their cyclic voltammetric data are discussed on the basis of the π-conjugation and interlayer π⋅⋅⋅π interactions in the molecular structures and the molecular orbitals. The barrier and mechanism of helical inversion are also reported.