Host‐Guest Chemistry and Nonlinear Optical Behaviors of Aluminum Molecular Rings

Comprehensive Summary Macrocyclic compounds are of great interest for their ability to capture guest molecules into their cavities. In particular, host‐guest interaction plays a crucial role in the formation of supramolecular compounds. Herein, two host‐guest supramolecular compounds, [Al8(OH)8(L)16]·2HL (HL@AlOC‐166, HL = 4‐Iodobenzoic acid) and [Al8(OH)8(L)8(L1)8]·2DMF (DMF@AlOC‐166, HL1 = isoamyl alcohol), are acquired by introducing different types of guest components based on the internal pore cavities of the aluminum molecular ring [Al8(OH)8(L)16] (AlOC‐166). The inclusion of these guests is attributed to the presence of abundant hydrophilic OH serving as the hydrogen bond donors inward the ring cavity. Host‐guest compounds usually exhibit superior nonlinear optical (NLO) response due to the existence of guest molecules that could change symmetry, dipole moments, charge distributions, etc. Unexpectedly, the AlOC‐166 achieved the best NLO results, although it had no guest molecules inside its molecular ring, which breaks the traditional concept. The reason for this trend can be explained by the difference in intermolecular force rather than intramolecular interaction, mainly related to the amount and strength of π···π and C—I···π interactions in different compounds. This work investigates the effect of host‐guest interaction on NLO, representing a new perspective for designing optical limiting materials. Host‐guest supramolecular compounds have long been a hot research topic. But the use of ligands is essential for the empty molecular ring to encapsulate the guest. Here, we chose 4‐iodobenzoic acid as the ligand and obtained two host‐guest superclusters. Their rich C—I···π and π ···π interactions have spurred an in‐depth exploration of the host‐guest chemistry on nonlinear optical properties.