Silver-Mediated Formation of a Cofacial Porphyrin Dimer with the Ability to Intercalate Aromatic Molecules

Biomimetic Recognition of Quinones in Water by an Endo-Functionalized Cavity with Anthracene Sidewalls

Selective molecular recognition in water is the foundation of numerous biological functions but is a challenge for most synthetic hosts. We employ the concept of endo-functionalized cavity and the strategy of simultaneous construction to address this issue. The concept and the strategy were demonstrated in the construction of a biomimetic host for selectively recognizing quinones in water. The host was synthesized by joining two pieces of bent anthracene dimer through amide bond formation, affording a deep hydrophobic cavity and inward-directing hydrogen bonding sites. The host can recognize quinones over their close analogues in water, and its association affinity to p-benzoquinone is the highest among all the known hosts and is even comparable to that of the bioreceptor. The binding with an anthraquinone reaches nanomolar affinity. Shielded hydrogen bonding, C-H⋅⋅⋅π, and charge transfer interactions, and the hydrophobic effect are responsible for the high binding affinity and selectivity.

Maximizing Coordination Capsule-Guest Polar Interactions in Apolar Solvents Reveals Significant Binding

Guest encapsulation underpins the functional properties of self-assembled capsules yet identifying systems capable of strongly binding small organic molecules in solution remains a challenge. Most coordination capsules rely on the hydrophobic effect to ensure effective solution-phase association. In contrast, we show that using non-interacting anions in apolar solvents can maximize favorable interactions between a cationic Pd₂ L₄ host and charge-neutral guests resulting in a dramatic increase in binding strength. With quinone-type guests, association constants in excess of 10⁸  m^-1 were observed, comparable to the highest previously recorded constant for a metallosupramolecular capsule. Modulation of optoelectronic properties of the guests was also observed, with encapsulation either changing or switching-on luminescence not present in the bulk phase.

A Perylene Bisimide Cyclophane as a "Turn-On" and "Turn-Off" Fluorescence Probe

A rigid, covalently linked perylene-3,4:9,10-tetracarboxylic acid bisimide (PBI) cyclophane was synthesized by imidization of a bay-substituted perylene bisanhydride with p-xylylenediamine. The interchromophoric distance of approximately 6.5 Å establishes an ideal rigid cavity for the encapsulation of large aromatic compounds such as perylene and anthracene with binding constants up to 4.6×10(4)  M(-1) (in CHCl3 ). For electron-poor guest molecules, the complexation process is accompanied by a significantly increased fluorescence, whereas the emission intensity is dramatically quenched by more electron-rich guests because of the formation of charge-transfer complexes. Furthermore, the influence of the PBI core twist on the binding constant results in a remarkable selectivity towards more flexible aromatic guest molecules.

Guest-induced transformation of a porphyrin-edged Fe(II)4L6 capsule into a Cu(I)Fe(II)2L4 fullerene receptor

The combination of a bent diamino(nickel(II) porphyrin) with 2-formylpyridine and Fe(II) yielded an Fe(II) 4 L6 cage. Upon treatment with the fullerenes C60 or C70 , this cage was found to transform into a new host-guest complex incorporating three Fe(II) centers and four porphyrin ligands, in an arrangement that is hypothesized to maximize π interactions between the porphyrin units of the host and the fullerene guest bound within its central cavity. The new complex shows coordinative unsaturation at one of the Fe(II) centers as the result of the incommensurate metal-to-ligand ratio, which enabled the preparation of a heterometallic cone-shaped Cu(I) Fe(II) 2 L4 adduct of C60 or C70 .