Proton Conductivity Switch for Hydrogen-Bonding Octaaminotetraphenylene Salts Through Crystal–Amorphous Transformation During H2O Sorption

The phosphate salt of octaaminotetraphenylene (OATP), [(H 4 OATP 4+ )(H 2 PO 4 – ) 4 ], was prepared. Single crystals were isolated with a crystal formula of (H 4 OATP 4+ )(H 2 PO 4 – ) 4 (H 3 PO 4 ) 0.25 ·2.5H 2 O, whereas the powder sample at 300 K formed an amorphous salt of (H 4 OATP 4+ )(H 2 PO 4 – ) 4.0 · n H 2 O with n = 1–2. In the anhydrous solids ( n = 0), the formation of a hydrogen-bonding network of H 2 PO 4 – anions and the dielectric relaxation associated with the motional freedom of H 2 PO 4 – were observed. Adsorption–desorption isotherms of H 2 O at 298 K showed the transformation between anhydrous amorphous (H 4 OATP 4+ )(H 2 PO 4 – ) 4 and hydrous crystalline (H 4 OATP 4+ )(H 2 PO 4 – ) 4 ·6H 2 O, and the proton conductivity increased by 2 orders of magnitude after H 2 O adsorption. The proton conductivity of hydrous salt reached 7.58 × 10 –5 S cm –1 . The cation–anion salt in the amorphous–crystalline transformation exhibited proton conductivity switching phenomena with an ON/OFF ratio of about 100 upon H 2 O adsorption–desorption.