Silver-Loaded Metalloporphyrin Ionic Covalent Organic Frameworks for Enhanced Optical Limiting Performance via Interfacial Charge Transfer and Plasmon Effects

Developing efficient covalent organic frameworks (COFs) with nonlinear optical (NLO) properties is of great significance for advanced optical devices. Herein, a series of two-dimensional (2D) metalloporphyrin-based ionic COFs decorated with Ag nanoparticles (Ag@COF(M), M = 2H, Ni, Co, Fe) are first obtained and subsequently dispersed into a polydimethylsiloxane (PDMS) matrix to form highly transparent and flexible COFs/PDMS glasses for practical optical limiting (OL) applications. The resulting Ag@COF(M) composites exhibit tunable OL responses depending on the type of metalloporphyrinic ligands. Among them, Ag@COF(Ni) exhibits the best optical limiting (OL) performance with a highest nonlinear absorption coefficient of 5.85 × 10-10 m W-1 and a lowest OL threshold of 6.25 J cm-2, outperforming other COF-based materials. Density functional theory (DFT) calculations are consistent with the experimental results, revealing that strong charge transfer between the COF(Ni) and Ag nanoparticles governs the NLO performance of Ag@COF(Ni). These findings not only provide a new strategy for designing high-performance NLO materials but also pave the way for developing flexible optical limiting devices.