Guest-Tuned Proton Conductivity of Porphyrinylphosphonate-Based Hydrogen-Bonded Organic Framework

Hydrogen-bonded organic frameworks (HOFs), similar to their MOF analogues, exhibit great potential in proton conduction applications. Herein, a porous HOF namely [(NiH4TPPP)(Me2NH2)4(DMF)(H2O)4] (UPC-H5) was synthesized from phosphonate-based porphyrinato nickel (NiH8TPPP), and its proton conductivity is regulated through a two-step guest change. Firstly, immersing UPC-H5 in CH2Cl2 to exchange lattice solvent molecules for 24 h followed by heating under vacuum afforded the lattice solvent molecule-free HOF [(NiH4TPPP)(Me2NH2)4] (UPC-H5a) with the pristine framework still retained. Secondly, exposing UPC-H5a to vapors of 25% aqueous ammonia for 24 h at room temperature gave a new derivative UPC-H5a@NH3·H2O with the molecular formula [(NiH4TPPP)(Me2NH2)2(NH4)2(H2O)4] according to elemental and thermal analyses. At 30 °C and 95% R.H., the proton conductivity of UPC-H5, UPC-H5a, and UPC-H5a@NH3·H2O amounts to 5.59 × 10−4, 7.00 × 10−3, and 1.47 × 10−2 S cm−1, respectively, which increases to 1.85 × 10−3, 3.42 × 10−2, and 1.59 × 10−1 S cm−1 at 80 °C and 99% R.H., clearly showing the effect of guest regulation on the proton conductivity of the HOF-based materials. In addition, this result is also helpful towards understanding the important role of guests in the formation of their proton conduction pathways.