The application of self-assembled hosts as "molecular flasks" has precipitated a surge of interest in the reactivity and properties of molecules within well-defined confined spaces. The facile and modular synthesis of self-assembled hosts has enabled a variety of hosts of differing sizes, shapes, and properties to be prepared. This Review briefly highlights the various molecular flasks synthesized before focusing on their use as functional molecular containers--specifically for the encapsulation of guest molecules to either engender unusual reactions or unique chemical phenomena. Such self-assembled cavities now constitute a new phase of chemistry, which cannot be achieved in the conventional solid, liquid, and gas phases.

Intrigued by transannular interactions occurring in stacked aromatic molecules, chemists have long endeavored to engineer discrete stacks of specific lengths and orientation. The maturation of self-assembly methodologies has shifted the focus away from utilizing covalent scaffolds to harnessing non-covalent interactions such as ionic interactions, hydrogen bonds, metal-ligand interactions, and aromatic interactions. Aromatic molecules often assemble into ill-defined, infinite aggregates and thus multiple self-assembly techniques must be combined to achieve the desired stack size and conformations. This critical review briefly highlights covalent scaffolds of stack aromatics before focusing on modern self-assembly based strategies for engineering discrete stacks of aromatic molecules (149 references).

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Auf kleinstem Raum: Selbstorganisierte Wirtmoleküle können als „molekulare Reaktionskolben“ die Reaktivitäten und Eigenschaften von Gastmolekülen verändern, die den räumlichen Einschränkungen ihrer wohldefinierten Hohlräume ausgesetzt sind. Vielfältige funktionale Wirte mit unterschiedlichen Größen, Formen und Anwendungsmöglichkeiten wurden mithilfe der einfachen, modularen Konzepte der supramolekularen Chemie hergestellt. Der Einsatz von selbstorganisierten Wirtmolekülen als “molekularen Reaktionskolben” hat das Interesse an der Reaktivität und den Eigenschaften von Molekülen in definierten Hohlräumen unter räumlicher Einschränkung enorm gesteigert. Die modulare Synthese selbstorganisierter Wirte ist einfach, und es wurden Systeme mit verschiedenen Größen, Formen und Eigenschaften hergestellt. In diesem Aufsatz gehen wir zunächst kurz auf die unterschiedlichen molekularen Reaktionskolben ein und konzentrieren uns anschließend auf ihren Einsatz als funktionale molekulare Behälter, besonders für den Einschluss von Gastmolekülen zur Verwirklichung ungewöhnlicher Reaktionen und zur Beobachtung einzigartiger chemischer Phänomene. Diese selbstorganisierten Hohlräume können als neuartige Phase angesehen werden, in der Reaktionen ablaufen, die in fester, flüssiger oder gasförmiger Phase nicht möglich sind.

Soluble copper-based M4L4 lantern-type metal-organic cages bearing internal amines were synthesized. The solution state integrity of the paramagnetic metal-organic cages was demonstrated using NMR, DLS, MS, and AFM spectroscopy. 1D supramolecular pillars of pre-formed cages or covalent host-guest complexes selectively formed upon treatment with 4,4'-bipyridine and acetic anhydride, respectively.

Red-emissive molecules have important applications as chemosensors, biological tags, and new light source materials but are severely limited by solubility and the tendency to form nonemissive aggregrates. Here we present an unusual example where a coordination cage sequesters and maintains the red-emissive properties of tetraazaporphine (TAP) in aqueous solution. Additionally, encapsulation within the highly cationic host lowers the pK(a) of the TAP interior protons, leading to the formation of an acid/base ON/OFF fluorescent switch.

Host-guest complexes involving M(6)L(4) coordination cages can display unusual photoreactivity, and enclathration of the very large fluorophore bisanthracene resulted in an emissive, mechanically trapped intramolecular exciplex. Mechanically linked intramolecular exciplexes are important for understanding the dependence of energy transfer on donor-acceptor distance, orientation, and electronic coupling but are relatively unexplored. Steady-state and picosecond time-resolved fluorescence measurements have revealed that selective excitation of the encapsulated guest fluorophore results in efficient energy transfer from the excited guest to an emissive host-guest exciplex state.

Micelles are a versatile class of molecular assemblies typically composed of aliphatic molecules with hydrophilic groups. Polyaromatic molecules with hydrophilic groups, on the other hand, usually do not assemble into micellar structures in water but rather form columnar, π-stacked architectures. This Minireview article focuses on the recent development of aqueous micellar nanostructures with multiple oligoarylene rods or polyaromatic panels. The new micelles with spherical polyaromatic shells, which we name "aromatic micelles", serve as functional molecular flasks with superior binding abilities for medium to very large molecules in water.