Record Aluminum Molecular Rings for Optical Limiting and Nonlinear Optics

Crystalline cluster materials, a class of functional motif aggregations, provide a great opportunity for tuning the properties stemming from the flexible and accurate variation of inorganic and organic compositions. In this study, we demonstrate the effects of functional ligand and ring size regulation on the structures and third‐order nonlinear optical (NLO) properties. Revealed by the single‐crystal X‐ray analysis results, aluminum molecular ring expansion is achieved by 2×9 and 3×6 strategies. In terms of the given organic shells, we further tuned the aluminum molecular ring sizes from 3.0 nm to 1.7 nm. The picosecond Z‐scan measurements results revealed that the third‐order NLO performances do not only depend on the general conjugate interactions but are also related to hydrogen bonding, polarizability, and ring sizes. The large nonlinear absorption coefficient and onset prove that the observed samples are promising candidates for the field of nonlinear optics. A synthetic approach to generate the largest aluminum molecular rings is presented. Their nonlinear optics (NLO) and optical limiting (OL) performance is studied by the Z‐scan technique. The results provide insights to understand the NLO structure–activity relationship and tune the NLO performance at a molecular level.