Boosting Photocatalytic Hydrogen Production of Porphyrinic MOFs: The Metal Location in Metalloporphyrin Matters

Metal-organic frameworks (MOFs) have demonstrated great potentials toward catalysis, particularly in the establishment of structure-property relationships. Herein, an unusual OOP (out-of-plane) porphyrin-based MOF, synthesized by controlling the metal ion release with an unprecedented In(OH)(3) precursor, possesses high stability and exhibits unexpectedly high photocatalytic hydrogen production activity, far surpassing the isostructural in-plane porphyrin-based MOF counterparts. In the MOF structure, indium ions not only form indium-oxo chains but also metalate the porphyrin rings in situ, locating above the porphyrin plane instead of fitting in a coplanar fashion into the cavity and affording an unusual OOP porphyrin. Control experiments demonstrate that the OOP In(III) ions readily detach from the porphyrin rings under light excitation, avoiding the fast back electron transfer and thus greatly improving electron-hole separation efficiency and photocatalytic performance. To our knowledge, this is an unprecedented report on boosting MOF photocatalysis on the basis of special metalloporphyrin behavior.