Tuning Electrical- and Photo-Conductivity by Cation Exchange within a Redox-Active Tetrathiafulvalene-Based Metal-Organic Framework

Abstract

To activate electronic and optical functions of the redox-active metal-organic framework, (Me₂ NH₂ )[In^III (TTFTB)]⋅0.7 C₂ H₅ OH⋅DMF (Me₂ NH₂ @1, TTFTB=tetrathiafulvalene-tetrabenzoate, DMF=N,N-dimethylformamide), has been exchanged by tetrathiafulvalenium (TTF^.+ ) and N,N'-dimethyl-4,4'-bipyridinium (MV²⁺ ). These cations provide electron carriers and photosensitivity. The exchange retains the crystallinity allowing single-crystal to single-crystal post-synthetic transformation to TTF@1 and MV@1. Both TTF^.+ and MV²⁺ enhance the electrical conductivity by a factor of 10² and the visible light induced photocurrent by 4 and 28 times, respectively. EPR evidences synergetic effect involving charge transfer between the framework redox-active TTFTB bridges and MV²⁺ . The results demonstrate that functionalization of MOF by cation exchange without perturbing the crystallinity extends possibilities to achieve switchable materials.

Keywords: methylviologen; post-synthetic modification; redox-active species; single-crystal to single-crystal transformation; tetrathiafulvalene.