A Rhombic Pt(II) Metallacycle with Enhanced Third-Order Nonlinear Optical Response and Optical Power Limiting Performance

Coordination-driven self-assembly provides an effective strategy for the precise construction of supramolecular nonlinear optical (NLO) materials, yet its potential in third-order NLO applications remains insufficiently explored. Herein, we report a rhombic Pt(II) metallacycle ( MPt ) constructed via Pt–N coordination-driven self-assembly, achieving markedly enhanced third-order NLO responses that are confirmed to originate from the formation of the metallacyclic structure. Benefiting from the enhanced spin–orbit coupling (SOC) induced by multinuclear Pt(II) nodes and framework rigidification, MPt promotes intersystem crossing (ISC), suppresses triplet-state nonradiative decay, prolongs the triplet-state lifetime to 8.18 μs and strengthens excited-state absorption (ESA). As a result, MPt displays pronounced reverse saturable absorption (RSA) at 532 nm, outperforming the benchmark NLO material C 60 . Furthermore, the fabricated MPt@PDMS film exhibits excellent optical power limiting (OPL) performance, with an effective nonlinear absorption coefficient (β eff ) of 1045.70 cm GW –1 and a low optical limiting threshold ( F OL ) of 0.23 J cm –2, placing it among the best-performing polymer-based OPL films reported to date. This work provides valuable insight into the rational design of high-performance supramolecular NLO assemblies and establishes supramolecular topological engineering as an effective strategy for amplifying third-order NLO responses.