Unraveling the Dynamic Molecular Motions of a Twin-Cavity Cage with Slow Configurational but Rapid Conformational Interconversions.

Featuring diverse structural motions/changes, dynamic molecular systems hold promise for executing complex tasks. However, their structural complexity presents formidable challenge in elucidating their kinetics, especially when multiple structural motions are intercorrelated. We herein introduce a twin-cavity cage that features interconvertible C3- and C1-configurations, with each configuration exhibiting interchangeable P- and M-conformations. This molecule is therefore composed of four interconnected chiral species (P)-C3, (M)-C3, (P)-C1, (M)-C1. We showcase an effective approach to decouple these sophisticated structural changes into two kinetically distinct pathways. Utilizing time-dependent 1H NMR spectroscopy at various temperatures, which disregards the transition between mirror-image conformations, we first determine the rate constant (kc) for the C3- to C1-configuration interconversion, while time-dependent circular dichroism spectroscopy at different temperatures quantifies the observed rate constant (kobs) of the ensemble of all the structural changes. As kobs ≫ ${{\rm { \gg }}}$ kc, it allows us to decouple the overall molecular motions into a slow configurational transformation and rapid conformational interconversions, with the latter further dissected into two independent conformational interchanges, namely (P)-C3 ← → ${ \mathbin{{\stackrel{\textstyle\rightarrow} { {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }$ (M)-C3 and (P)-C1 ← → ${ \mathbin{{\stackrel{\textstyle\rightarrow} { {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }$ (M)-C1. This work, therefore, sheds light on the comprehensive kinetic study of complex molecular dynamics, offering valuable insights for the rational design of smart dynamic materials for applications of sensing, separation, catalysis, molecular machinery, etc.

A donor-acceptor cage for circularly polarized TADF emission.

Herein, we report the first example of chiral donor-acceptor cage DA-2 displaying efficient circularly polarized thermally activated delayed fluorescence (CP-TADF) with |glum| values up to 2.1 × 10-3 and PLQY of 32%. A small ΔEST of 0.051 eV and quasi-parallel (θ = 6°) transition electric and magnetic dipole moments were realized from the through-space charge transfer interaction between the parallelly aligned donor and acceptor in DA-2. This D-A cage configuration has provided a novel design strategy for discovering potential efficient CP-TADF emitters.

A Pair of Interconverting Cages Formed from Achiral Precursors Spontaneously Resolve into Homochiral Conformers.

Without chiral induction the emergence of homochirality from achiral molecules is rather serendipitous, as the rationale is somewhat ambiguous. We herein provide a plausible solution. From achiral precursors are formed a pair of interconverting cage conformers that exhibit a C3 -axis as the only symmetry element. When their interconversion is impeded with intramolecular H-bonding, each conformer self-sorts into a homochiral crystal, which is driven by a helical network of multivalent intermolecular interactions during the self-assembly of homochiral cage conformers. As no chiral induction is involved throughout, we believe our study could enlighten the rational design for the emergence of homochirality with several criteria: 1) formation of a molecule without inversion center or mirror plane; 2) suppression of the enantiomeric interconversion, and introduction of multivalent interactions along the helical trajectory of screw symmetry within the resulting superstructure.

Heterochiral Diastereomer-Discriminative Diphanes That Form Hierarchical Superstructures with Nonlinear Optical Properties.

In order to study the emergence of homochirality during complex molecular systems, most works mainly concentrated on the resolution of a pair of enantiomers. However, the preference of homochiral over heterochiral isomers has been overlooked, with very limited examples focusing only on noncovalent interactions. We herein report on diastereomeric discrimination of twin-cavity cages (denoted as diphanes) against heterochiral tris-(2-aminopropyl)amine (TRPN) bearing triple stereocenters. This diastereomeric selectivity results from distinct spatial orientation of reactive secondary amines on TRPN. Homochiral TRPNs with all reactive moieties rotating in the same way facilitate the formation of homochiral and achiral meso diphanes with low strain energy, while heterochiral TRPNs with uneven orientation of secondary amines preclude the formation of cage-like entity, since the virtual diphanes exhibit considerably high strain. Moreover, homochiral diphanes self-assemble into an acentric superstructure composed of single-handed helices, which exhibits interesting nonlinear optical behavior. Such a property is a unique occurrence for organic cages, which thus showcases their potential to spawn novel materials with interesting properties and functions.

Spontaneous Resolution of Racemic Cage-Catenanes via Diastereomeric Enrichment at the Molecular Level and Subsequent Narcissistic Self-Sorting at the Supramolecular Level.

The spontaneous resolution of racemates, from natural compounds to artificial structures, has long been pursued to shed light on the origin of homochirality in life. Even though diverse synthetic systems have been elegantly devised to elaborate the underlying principles of spontaneous symmetry breaking, their complexity is still unparalleled to the natural masterpieces including DNA helix and proteins, which convey remarkable coalescence at both molecular and supramolecular levels. Here, we report on the spontaneous resolution of a pair of homochiral entities from a racemic mixture of a triply interlocked cage-catenane comprising 720 possible stereoisomers. This cage-catenane comprises six methyldithiane ring-containing linkers (denoted rac-2). As each methyldithiane ring has two chiral centers, it exhibits four possible diastereomers. These otherwise equimolar diastereomers are preferentially differentiated with the equatorial conformers over their axial analogues, leading to the dominant formation of (S, R)-2 and (R, S)-2, i.e., diastereomeric enrichment at the molecular level. This diastereomeric enrichment is unbiasedly transferred from precursor rac-2 to cage-catenane rac-4, from which a pair of homochirals (S, R)6-4 and (R, S)6-4 is narcissistically self-sorted upon crystallization. This powerful symmetry breaking is attributed to a supramolecular synergy of directional π-π stacking with the multivalency of erstwhile weak S···S contacts (with an unusual distance of 3.09 Å) that are cooperatively arranged in a helical fashion. This work highlights the attainability of complex homochiral entities by resorting to coalesced covalent and noncovalent contributions and therefore provides additional clues to the symmetry breaking of sophisticated yet well-defined architectures.