Rare Guest-Induced Electrical Conductivity of Zn-Porphyrin Metallacage Inclusion Complexes Featuring -Donor/Acceptor/Donor Stacks

Charge-transfer (CT) interactions between co-facially aligned pi-donor/acceptor (pi-D/A) arrays engender unique optical and electronic properties that could benefit (supra)molecular electronics and energy technologies. Herein, we demonstrate that a tetragonal prismatic metal-organic cage (MOC1(8+)) having two parallel pi-donor tetrakis(4-carboxyphenyl)-Zn-porphyrin (ZnTCPP) faces selectively intercalate planar pi-acceptor guests, such as hexaazatriphenylene hexacarbonitrile (HATHCN), hexacyanotriphenylene (HCTP), and napthanelediimide (NDI) derivatives, forming 1:1 pi A@MOC1(8+) inclusion complexes featuring supramolecular pi-D/A/D triads. The pi-acidity of intercalated pi-acceptors (HATHCN >> HCTP approximate to NDIs) dictated the nature and strength of their interactions with the ZnTCPP faces, which in turn influenced the binding affinities (K-a) and optical and electronic properties of corresponding pi A@MOC1(8+) inclusion complexes. Owing to its strongest CT interaction with ZnTCPP faces, the most pi-acidic HATHCN guest enjoyed the largest K-a (5 x 10(6) M-1), competitively displaced weaker pi-acceptors from the MOC1(8+) cavity, and generated the highest electrical conductivity (2.1 x 10(-6) S/m) among the pi A@MOC1(8+) inclusion complexes. This work demonstrates a unique through-space charge transport capability of pi A@MOC1(8+) inclusion complexes featuring supramolecular pi-D/A/D triads, which generated tunable electrical conductivity, which is a rare but much coveted electronic property of such supramolecular assemblies that could further expand their utility in future technologies.