Amplifiable Symmetry Breaking in Aggregates of Vibrating Helical Molecules

Abstract

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.

Frontiers in circularly polarized luminescence: molecular design, self-assembly, nanomaterials, and applications

“…Developing excellent CPL-active materials with both high g lum and Φ is of great significance [68,69]. With the rapid development of supramolecular chemistry in the past several decades, chiral supramolecular self-assemblies and co-assemblies have been assigned to be one of the most suitable and promising CPL-active materials [70][71][72][73]. These chiral self-assemblies and co-assemblies with designable microstructures could provide a powerful approach to precisely regulate the arrangement of building blocks and promote the amplified CPL signals during assembly process via noncovalent interactions (π-π stacking, hydrogen bonds, hydrophobic interactions, van der Waals interactions, and hostguest interactions) [10,14,43,[74][75][76][77][78][79].…”

Efficient circularly polarized thermally activated delayed fluorescence hetero-[4]helicene with carbonyl-/sulfone-bridged triarylamine structures

“…Generally, there are only a few studies on the chiral properties of [4]helicenes, owing to their extremely low racemization barrier. 39,40 Here, although the enantiomers of QPO are not completely separated via chiral high-performance liquid chromatography (HPLC) at room temperature, QPO has shown obvious enantiomeric phenomena from chiral HPLC analysis, due to its twisted and asymmetric molecular structure (Fig. S6-S12, ESI †).…”

“…39 Notably, the enantiomers of QPO cannot be completely resolved via chiral HPLC at room temperature, owing to the low racemization barrier of [4]helicene. 39,40 Consequently, resolution of the P-and M-isomers of QPO is impossible. By contrast, the enantiomers of QPO-PhCz, i.e., (P)-QPO-PhCz/(M)-QPO-PhCz, can display chirality with large racemic energy barriers because of the bulkier steric hindrance between the PhCz moiety and the QPO group, which is beneficial for obtaining a luminescence dissymmetry factor (g lum ) of up to 1.2 Â 10 À3 in dichloromethane solution.…”

Biased Symmetry Breaking and Chiral Control by Self‐Replicating in Achiral Tetradentate Platinum (II) Complexes

“…The specific AIE‐active achiral molecules show an odd‐even dependent symmetry breaking in crystallization [37] . The azahelicene with achiral vibrating helical conjugated structure displays biased symmetry breaking, which forms enantiomerically enriched domains, resulting in more stable homochiral aggregates [38] . It is well known that for some bent‐core organic molecules symmetry breaking occurs in the liquid crystals (LCs) phase, leading to the formation of chiral conglomerates which consist of the domains with opposite handedness, [16, 39–44] but the biased symmetry breaking in LCs has not been observed up to now.…”