Coordination-Induced Symmetry Breaking on Metal-Porphyrinic Framework Thin Films for Enhanced Nonlinear Optical...

Structural asymmetry affecting the nonlinear optics (NLO) of metal-organic frameworks (MOFs) is very important in fundamentals and applications but is still a challenge. Herein we develop a series of indium-porphyrinic framework (InTCPP) thin films and provide the first study on the coordination-induced symmetry breaking on their third-order NLO. The continuous and oriented InTCPP(H₂) thin films were grown on quartz substrates and then postcoordinated with different cations (Fe²⁺ or Fe³⁺Cl^-) in InTCPP(H₂) (named InTCPP(Fe²⁺) and InTCPP(Fe³⁺Cl^-)). The third-order NLO results reveal the Fe²⁺ and Fe³⁺Cl^- coordinated InTCPP thin films have substantially enhanced NLO performance. Moreover, InTCPP(Fe³⁺Cl^-) thin films cause symmetry breaking of microstructures, resulting in a 3-fold increase in the nonlinear absorption coefficient (up to 6.35 × 10^-6 m/W) compared to InTCPP(Fe²⁺). This work not only develops a series of nonlinear optical MOF thin films but also provides new insight into symmetry breaking on MOFs for nonlinear optoelectronic applications.