where f is the proportion of the dye localized in the first environment, KSV1 and KSV2 are the Stern-Volmer constants for the first and the second environment. Fig. shows that already for PCN-224 based on free-base porphyrin the quenching is very efficient: the fluorescence intensity decreases by more than 4-fold at air saturation comparing to anoxic conditions. For comparison, the quenching of the same magnitude is observed for Pt(II) porphyrins (such as Pt(II)TFPP) immobilized in polystyrene. Notably, the luminescence decay time of Pt(II)TFPP in polystyrene is roughly 4 orders of magnitude longer (55 µs) than that of H2TCPP in PCN-224 (6.7 ns). Such an efficient quenching in a MOF can be explained by the fact that the porphyrin molecules are structural elements of the porous channels and thus are freely exposed to oxygen molecules that diffuse through them. In contrast, even in polymers with high free-volume polymer chains surround the indicator molecule partly protecting it from interaction with oxygen. It is therefore likely that oxygen permeability in PCN-224 is higher than that of poly(trimethylsilylpropyne) (PTMSP), a polymer with the highest oxygen permeability known. To verify this, we embedded a lipophilic analogue of H2TCPP, namely 5,10,15,20-tetrakis-(4-methoxycarbonylphenyl)-21,23H-porphyrin (H2TMCPP) into PTMSP and investigated its oxygen response (Fig. ). The Stern-Volmer constant obtained for this material is 0.073 kPa -1 which is about 3.5-fold lower than for PCN-224 (0.25 kPa -1 ) despite the longer 0 of H2TMCPP in PTMSP (10.7 ns).