Introduction
Porphyrins are macromolecular heterocyclic compounds composed of porphin (C20H14N4) substituted by various functional groups at the meso-position or β-position, which were first investigated in 1889, when they were extracted from the heme of animals or chlorophyll. Metal-organic frameworks (MOFs) are crystalline porous materials comprising metal ions and highly versatile organic linkers. Among the different families of functional organic linkers that have been employed in synthesizing MOFs, porphyrin-based linkers have garnered special attention owing to their unique geometry and versatile functionality. The porphyrin, as a multifunctional linker unit, has square-planar geometry, rigidity, thermal stability and high modifiability and thus rendering the MOFs stable. In addition, porphyrins and their derivatives have remarkable optical and electronic properties, endowing MOFs with optical and electronic properties. As such, there have been increasing interests over the past two decades in the study of MOFs based on porphyrin linkers, and these MOFs have unique and versatile applications such as photocatalysis, electrocatalysis, biomimetic catalysis, sensing and biomedicine [1].
Fig. 1. Representative molecular structures of porphyrin organic linkers used for the synthesis of MOFs.
Applications
As valuable and promising organic linkers, porphyrin linkers have been widely used in the construction of various MOFs, and the obtained MOFs have been applied in many fields. The details are as follows.
- Synthesis of MOFs for photocatalysis: Owing to their conjugated macrocyclic structure, porphyrins possess several important features for catalysis, and in particular for photocatalysis. And thus, evolving as interesting linkers, porphyrins can be used to synthesize MOFs with photocatalytic activity, and offer versatile functionality that can be harnessed for visible-light responsive photocatalysis. The potential applications of porphyrin-containing MOFs in photocatalysis include hydrogen evolution, carbon dioxide reduction, oxidation via singlet oxygen production alcohol oxidation, and Fenton-type chemistry amongst others. For example, Fateeva et al. constructed a water-stable porphyrinic MOF, Al-PMOF, comprised of tetrakis(4-carboxyphenyl)-porphyrin (H4TCPP) linkers and Al(OH)O4 chain nodes, which can be used in photocatalytic evolution of H2 from water [1].
Fig. 2. The structure of Al-PMOF featuring porphyrin linkers for hydrogen evolution.
- Synthesis of MOFs for electrochemistry: As mentioned earlier, porphyrins have good catalytic activity and thus can also be used to synthesize MOFs for electrocatalysis. The porphyrin containing MOFs can be integrated onto a conductive substrate for electrochemical catalysis of hydrogen evolution, oxygen evolution, oxygen reduction reaction (ORR), and carbon dioxide reduction. Moreover, the use of MOFs based on porphyrins linkers in other electrochemical applications accomplished the electrocatalytic detection of hydrogen peroxide, uric acid, xanthine, and hypoxanthine or even the reduction of other inert moieties. For example, a copper-containing MOF, Cu2(CuTCPP), was synthesized by porphyrin linker and was used for the electroconversion of carbon dioxide to formate and acetate.
Fig. 3. Structure of Cu2(CuTCPP) featuring Cu2 nodes and porphyrin linkers for the electrochemical reduction of CO2 to formate and acetate.
- Synthesis of MOFs for sensing: Porphyrins are frequently used to synthesize MOFs with application of sensing. Because the unique catalytic, electrochemical and photophysical properties accessible in porphyrin linkers, combined with high porosity of MOFs, result in porphyrin-based MOFs as ideal candidates for sensing-related applications. They can serve as high performing sensing platforms for the detection of a variety of molecules and ions such as toxic chemical/pollutant (nitroaromatic explosives, pesticides, heavy metals, and anions), pH, biomolecules, antigens, enzymatic activity, etc.
Fig. 4. Schematic illustration of the electrochemiluminescence kinase activity assay using MOF-525 featuring porphyrin linkers.
- Synthesis of MOFs for biomedicine: Porphyrins have potent biological properties, such as biocompatibility, effective clearance, long residence time in tumors, few side effects, and the mimicking of various biological functions, which are extremely useful for biomedical applications. In addition, porphyrins and their derivatives are widely used as photosensitizers (PSs) for photodynamic therapy (PDT) and fluorescent probes in imaging-guided therapy. Thus, it is preferred to construct MOFs materials used in biomedicine by using porphyrins as linker. The obtained MOFs exhibit a remarkable PDT effect and synergistic effect, and have a high drug–loading capacity because of their excellent electrochemical properties and large surface area. Moreover, these MOFs can be artificially endowed with imaging properties such as fluorescence imaging, magnetic resonance imaging (MRI), computed tomography (CT), photoacoustic imaging (PAI), and single photon emission computed tomography (SPECT), which can show patient’s physiological response and clinical needs rapidly and directly [2].
Alfa Chemistry offers a series of porphyin MOFs linkers, which have been widely used to construct MOFs for biomimetic catalysis, electrocatalysis, photocatalysis, sensing and biomedicine. You can click on our product list for a detailed view. At the same time, we also offer product customization according to customer's detailed requirements. If you are interested in our products or have any questions or needs, please feel free to contact us. We will be happy to provide you with support and services.
References:
- Zhang X., et al. A historical perspective on porphyrin-based metal–organic frameworks and their applications[J]. Coordination chemistry reviews, 2021, 429: 213615.
- Wang Z., et al. Recent advances in porphyrin-based MOFs for cancer therapy and diagnosis therapy[J]. Coordination Chemistry Reviews, 2021, 439: 213945.
