It is of great interest to modulate the photophysical properties by atomically precise chemical control. The incorporation of conjugated ligands into crystalline materials provides a platform for molecular‐level interpretation of the structure‐activity relationship. Herein, we reported the phenol‐thermal and scale‐up synthesis of a new family of remarkably stable aluminum molecular rings. They are assembled by twenty AlIII ions with large conjugated ligands and phenols, representing the currently largest sizes (up to 4 nm in diameter) in the field of main group metal oxo clusters. Phenols are not only reaction medium but also auxiliary bridging ligands on the surface of macrocyclic molecules. In addition, they are either parallel to the center of the molecular ring or inserted into the molecular ring, or form dimers/tetramers that bind macrocyclic molecules to form supramolecular structures. These macrocyclic rings are hydrophobic and ultra‐stable, evidenced by retaining their morphology and crystalline when exposed to air for more than a year. Compared with the pristine conjugated ligands, they exhibit coordination‐enhanced fluorescence. By dispersing them into a polydimethylsiloxane (PDMS) matrix, we prepared transparent and flexible PDMS thin films for coupling flexible display and nonlinear optical application. Our discovery of such atomically precise rings provides a platform for the fine‐tuning of photo‐related performances.

The hydrolysis of earth‐abundant AlIII has implications in mineral mimicry, geochemistry and environmental chemistry. Third‐order nonlinear optical (NLO) materials are important in modern chemistry due to their extensive optical applications. The assembly of AlIII ions with π‐conjugated carboxylate ligands is carried out and the hydrolysis and NLO properties of the resultant material are studied. A series of Al32‐oxo clusters with hydrotalcite‐like cores and π‐conjugated shells are isolated. X‐ray diffraction revealed boundary hydrolysis occurs at the equatorially unsaturated coordination sites of AlIII ions. Charge distribution analysis and DFT calculations support the proposed boundary substitution. The Al32‐oxo clusters possess a significant reverse saturable absorption (RSA) response with a minimal normalized transmittance up to 29 %, indicating they are suitable candidates for optical limiting (OL) materials. This work elucidates the hydrolysis of AlIII and provides insight into layered materials that also have strong boundary activity at the edges or corners.

Comprehensive Summary The synthesis of heterometallic aluminum‐based materials is challenging yet attractive, due to their potential applications in optics, catalysis, magnetism and semiconductor device. We have now successfully synthesized two Al7Ni2 heterometallic clusters bearing different peripheral alkoxide ligands through a heterometal substitution strategy. Single crystal structure analysis shows that they are isostructural, only with slight differences in the number of OH and guests. We found that benzyl alkoxides protected Al7Ni2 cluster compound is more stable in H2O and various organic solvents when compared with ethoxides coordinated one. Moreover, it can be used as a reliable catalyst in aldol condensation reactions with higher activity. This work provides a new method for the design of stable crystalline heterometallic aluminum oxo compounds and reveals their excellent catalysis performance.