As was shown in Fig. , Pt(II)PCN-224 is extremely sensitive to molecular oxygen in gas phase showing almost 6-fold quenching of phosphorescence intensity already at 0.2 kPa O2. On the other hand, the same material was reposted to show about 3-fold quenching of luminescence intensity in air-saturated aqueous dispersion (21 kPa O2). Such drastic difference in the sensitivity (about 200fold) can be explained by substitution of the gas phase inside the pores of the MOF by aqueous phase. Even for measurement in the gas phase, residual solvents including water can be trapped inside the MOF and thus hinder diffusion of oxygen through the pores. In fact, the extreme oxygen quenching capabilities of MOFs could only be achieved when the materials were fully activated by treatment in vacuum and at elevated temperature (0.7 mbar, 120 °C, 72 h). Fig. and shows the humidity influence on the sensing properties of PCN-224. As can be seen, an increase of relative humidity from 0 to 33% results in some decrease of fluorescence intensity and sensitivity of the material. The behaviour is reversible and the parameters are recovered when dry conditions are established again (Fig. ). Increasing relative humidity to 53% results in further decrease of sensitivity (Fig. ), again reversible. However, if the humidity is raised to 84%, a drastic decrease of the sensitivity is observed. Comparison of KSV values at 0 and 84% relative humidity (0.25 kPa -1 and 0.008 kPa -1 , respectively) reveals the decrease of sensitivity by about 30-fold. Notably, this effect cannot be reversed by changing back to dry atmosphere but only by activation of the material at elevated temperature and vacuum. The drastic decrease of sensitivity at high humidity may be due to condensation of water inside of the porous channels of the MOF. In this respect substitution of meso-tetracarboxyphenyl porphyrin with (partly) fluorinated analogues may be a promising way to reduce or even completely overcome the above limitation. Porphyrins bearing fluorine atoms in -position are known, and partial fluorination in the meso-phenyl positions is likely to be feasible.