Guest-tuned proton conductivity of a 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 [(NiH 4 TPPP)(Me 2 NH 2 ) 4 (DMF)(H 2 O) 4 ] (UPC-H5) was synthesized from phosphonate-based porphyrinato nickel (NiH 8 TPPP), and its proton conductivity is regulated through a two-step guest change. Firstly, immersing UPC-H5 in CH 2 Cl 2 to exchange lattice solvent molecules for 24 h followed by heating under vacuum afforded the lattice solvent molecule-free HOF [(NiH 4 TPPP)(Me 2 NH 2 ) 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@NH 3 ·H 2 O with the molecular formula [(NiH 4 TPPP)(Me 2 NH 2 ) 2 (NH 4 ) 2 (H 2 O) 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@NH 3 ·H 2 O 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. A porous porphyrin-based hydrogen-bonded organic framework (HOF) was constructed, and its proton conductivity was improved through a two-step guest-tuned strategy. After regulation, the proton conductivity of the HOF reaches 1.59 × 10 −1 S cm −1 at 80 °C and 99% RH.