Dual-Modulating Third-Order Nonlinear Optics of Metal–Organic Clusters via Lanthanide Contraction and Photoaddition

The precise atomic-level modulation of third-order nonlinear optical (NLO) properties in lanthanide-organic clusters represent a formidable challenge in advanced photonic materials and technologies. Herein, we demonstrate a dual-modulation strategy combining the lanthanide contraction effect and ligand photoaddition to systematically tailor the structure and NLO responses of a series of lanthanide-organic clusters from a photosensitive 9-anthracenecarboxylic acid (AC) ligand: CAS-7(La ∼ Dy), CAS-8(Ho ∼ Yb), CAS-9(Lu), and the photopolymerized CAS-7(UV). Z-scan results indicate that the obtained clusters exhibit reverse saturable absorption (RSA) with strong optical limiting performance. A progressive decrease in optical limiting performance is observed from CAS-7 to CAS-9 with increasing lanthanide atomic number. Notably, exposure to 365 nm light induces the polymerization of CAS-7 to form CAS-7(UV), showing markedly enhanced NLO properties. The mechanism behind the tunability is attributed to subtle polarization changes modulated by the lanthanide contraction effect, while the photoactivation stems from a [4 + 4] cycloaddition of the AC ligand. This work establishes a versatile dual-modulating approach for precise manipulation of NLO behavior, opening pathways for advanced nonlinear photonic applications.