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Interpenetrated Metal-porphyrinic Framework Developed for Enhanced Nonlinear Optical Limiting
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Third-order nonlinear optical (NLO) materials have attracted interest because of their applications in the areas such as the optical switching, optical limiting (OL) and mode-locked laser systems. Particularly, NLO materials with OL property can be used to protect human eyes and sensitive optical instruments from laser induced damage.
Porphyrin based metal-organic frameworks (MOFs) have been recently developed to study their OL performance by introducing tunable metallized porphyrinic ligands, adjusting morphology, and loading guest molecule or doping carbon materials in MOFs. But structural interpenetration in MOFs structure has not been realized to enhance their OL effect.
In a study published in J. Am. Chem. Soc., the research group led by Prof. ZHANG Jian and Prof. GU Zhigang from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences reported a two-fold interpenetrated MOF [Zn2(TPyP)(AC)2] and a non-interpenetrated MOF [Zn3(TPyP)(H2O)2(C2O4)2] constructed from 5,10,15,20-Tetra(4-pyridyl)porphyrin (TPyP(H2)) ligand (AC = acetate, C2O4 = oxalate).
The researchers found that the [Zn2(TPyP)(AC)2] achieved excellent OL performance with giant nonlinear absorption coefficient and large third-order susceptibility, which was much better than [Zn3(TPyP)(H2O)2(C2O4)2] and other reported OL materials.
They dispersed the MOF nanosheets into polydimethylsiloxane (PDMS) matrix to form highly transparent and flexible MOFs/PDMS glasses for practical nonlinear optical applications. The [Zn2(TPyP)(AC)2]/PDMS with excellent flexibility and endurance displayed higher β than that of [Zn3(TPyP)(H2O)2(C2O4)2]/PDMS. The OL response can be optimized by adjusting the concentration of [Zn2(TPyP)(AC)2] in PDMS matrix and the types of matelloporphyrinic groups.
Besides, the researchers carried out density functional theory (DFT) calculations to understand the origin of NLO properties of [Zn2(TPyP)(AC)2]. They demonstrated that the abundant π-π interaction between two individual frameworks in interpenetrated [Zn2(TPyP)(AC)2] increased the electron delocalization/transfer and boosted the NLO response in [Zn2(TPyP)(AC)2].
This study provides a new way to enhance OL performance by constructing interpenetrated structures and a new way to prepare transparent and flexible MOF composites in nonlinear optical applications. This is the first study to enhance OL effect by building interpenetration in MOF materials.
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