Tuning Proton Conductivity by Interstitial Guest Change in Size-Adjustable Nanopores of a Cu -MOF: A Potential Platform for Versatile Proton Carriers.

By exploiting the breathing behavior of nanopores, we have studied for the first time the dependency of the guest-induced proton conductivity of an interpenetrated Cu metal-organic framework (Cu -MOF, [1]) on various guest molecules. Proton conductivities of over 10  S cm under humid conditions were induced by a series of guest molecules, namely N,N-dimethylformamide, dimethyl sulfoxide, diethylamine, 1,4-dinitrobenzene, nitrobenzene, pyridine, and 1H-1,2,4-triazole. A detailed investigation of the guest-incorporated complexes revealed that low-energy proton conduction occurs under humid conditions through the Grotthuss mechanism in [1⊃NB] and through the vehicle mechanism in the rest of the complexes. Single-point energy computations revealed considerable stabilization upon guest encapsulation. To the best of our knowledge, [1] represents the first example in which considerably high protonic conductivity is triggered upon the facile incorporation of small molecules of such a variety. The investigation portrayed herein may be a stepping stone towards the rational design of proton-conducting materials for practical applications.