Colorimetric detection of trace water in tetrahydrofuran using N,N '-substituted oxoporphyrinogens

Oxoporphyrinogens (OxPs) bind water molecules at pyrrolic NH and quinonoid carbonyl groups leading to visible colour changes due to variation in the pi-electronic structure of OxPs. Introduction of hydrophilic substituents at two pyrrole NH groups improves sensitivity to H2O, and one OxP derivative is a colorimetric indicator of trace H2O (similar to 50 ppm) in THF.