Ligand modification on organotin-oxo clusters for enhanced third-order nonlinear optical response

Abstract

Elucidating the influence of intermolecular weak interactions on third-order nonlinear optical (TONLO) responses remains a significant challenge in materials science. Herein, two isostructural enantiomeric pairs of tetranuclear organotin-oxo clusters, denoted as D/L-Sn₄-Boc and D/L-Sn₄-Cbz, were synthesized via a solvothermal approach. Both clusters feature an identical distorted S-shaped framework, functionalized with chiral alanine derivatives bearing tert-butoxycarbonyl (Boc) or benzyloxycarbonyl (Cbz) groups. The peripheral alkyl and aryl substituents impart remarkable chemical robustness and hydrophobicity. Notably, the presence of an additional benzene ring in the Cbz-functionalized carboxylate ligand introduces more C–H⋯π interaction sites relative to the Boc-functionalized analogue, shortening the contact distance from 3.06 to 2.89 Å and inducing a more compact helical packing. Consequently, the Cbz-modified cluster exhibits a substantially enhanced nonlinear absorption coefficient (β = 3.5 × 10⁻⁸ m W⁻¹) compared to the Boc-modified analogue (β = 1.0 × 10⁻⁸ m W⁻¹). This study demonstrates that subtle ligand modifications can effectively tune weak intermolecular forces, thereby offering a viable strategy for optimizing the TONLO performance of metal-oxo clusters.