A distinct reversible colorimetric and fluorescent low pH response on a water-stable zirconium–porphyrin metal–organic framework

A water stable zirconium-porphyrin MOF (PCN-222) was synthesized according to the reported method and found to produce a distinct reversible colorimetric and fluorescent "turn-off-turn-on" pH response. The colorimetric response is achieved under acidic conditions starting at pH ~3 and persists under concentrated acidic conditions. To the best of our knowledge, this is the first report of a colorimetric MOF pH sensor.