Another promising way to construct in first sight "matrix-free" indicators is to incorporate the dyes into metal-organic frameworks (MOFs). MOFs are typically crystalline materials that generally consist of metal nodes and organic linkers and are usually characterized by an extremely high porosity. The great variety of organic linkers and metal nodes enables a huge structural diversity of MOFs, including the synthesis of luminescent variants. Due to the permanent porosity and high accessibility to gases in the framework, these materials are promising for sensing applications including oxygen quantification. The oxygen sensing-unit can be either a structural element of the porous network or, alternatively, be incorporated into the pores during synthesis or via postsynthetic incubation. Incorporation into the pores during synthesis does not allow for much control over the distribution of the indicator dye within the framework that is reflected in distinctly nonlinear Stern-Vollmer plots due to different oxygen accessibilities within the crystal. Additionally, such materials may be prone to leaching of the indicator out of the pores although it can be minimized via design of the pore structure. On the other hand, incorporation of a sensing element as a MOF building block not only eliminates leaching but also potential aggregation of dyes that may negatively affect the luminescent and sensing properties. Porphyrins are excellent organic linkers for the construction of MOFs and many different frameworks have been described over the last decades. Unfortunately, many of them are prone to hydrolysis and are therefore of limited interest for sensing applications under ambient conditions. One well-described and hydrolytically considerably stable porphyrin-based MOF is PCN-224. PCN-224 consists of Zr6 clusters which are connected by tetrakis-(4-carboxyphenyl) porphyrin (H2TCPP) as organic linker and is sufficiently insoluble in most common solvents as well as hydrolytically stable in a broad pH range (1 to 11). This MOF has a permanent porosity with a reported BET surface of 2600 m² g -1 and large pore sizes of 1.9 nm in diameter. These properties renders PCN-224 and closely related MOFs attractive for many applications such as (photo)catalysis, photodynamic therapy or drug delivery. However, the luminescence properties of the PCN-224 in context of oxygen sensing in the gas phase have not been investigated. Only the Pt(II) derivative of PCN-224, Pt(II)PCN-224, was used for realtime monitoring of dissolved oxygen in aqueous dispersion. The MOF was demonstrated to respond to oxygen in physiologically relevant concentration range showing about 3-fold quenching of luminescence intensity in air-saturated conditions. Such sensitivity is comparable to that of the materials prepared by immobilization of Pt(II) porphyrins in polystyrene or poly(methylmethacrylate) and is much lower than it would be expected from highly porous MOFs. In this work we investigate the effect of molecular oxygen on luminescent properties of three MOFs: the fluorescent PCN-224 based on the metal-free porphyrin linker and the phosphorescent analogues Pt(II)PCN-224 and Pd(II)PCN-224. We will show that the porous framework ensures excellent accessibility of the porphyrin emitters to molecular oxygen and thus unprecedentedly high bimolecular quenching constants. Very efficient quenching in the gas phase is observed already for fluorescent PCN-224 MOF, whereas the luminescence of the metalated analogues is quenched by traces of molecular oxygen. Pd(II)PCN-224 MOF belongs to one of the most oxygen sensitive materials reported so far. In fact, the sensitivity of the Pd(II)PCN-224 MOF exhibiting a Stern-Volmer constant (KSV) of 2610 kPa -1 surpasses by far the sensitivity of known trace oxygen sensors based on Pd(II) porphyrins immobilized into porous silica-gel matrix (KSV of 67 kPa -1 ). In this contribution we will also show how the MOFs can be conveniently immobilized onto different materials a step necessary to improve their handling in sensing applications.