Supramolecular Recognition within a Nanosized Buckytrap That Exhibits Substantial Photoconductivity

We report here a nanosized buckytrap, 1, constructed from two bis-zinc(II) expanded-TTF (exTTF) porphyrin subunits. Two forms, 1a and 1b, differing in the axial ligands, H2O vs tetrahydrofuran (THF), were isolated and characterized. Discrete host-guest inclusion complexes are formed upon treatment with fullerenes as inferred from a single-crystal X-ray structural analyses of 1a with C70. The fullerene is found to be encapsulated within the inner pseudohexagonal cavity of 1a. In contrast, the corresponding free-base derivative (2) was found to form infinite ball-and-socket type supramolecular organic frameworks (3D-SOFs) with fullerenes, (2 center dot C60)n or (2 center dot C70)n. This difference is ascribed to the fact that in 1a and 1b the axial positions are blocked by a H2O or THF ligand. Emission spectroscopic studies supported a 1:1 host-guest binding stoichiometry, allowing association constants of (2.0 +/- 0.5) x 104M-1 and (4.3 +/- 0.9) x 104 M-1 to be calculated for C60 and C70, respectively. Flash-photolysis time -resolved microwave conductivity (FP-TRMC) studies of solid films of the Zn-complex 1a revealed that the intrinsic charge carrier transport, i.e., pseudo-photoconductivity (O n-ary sumation I4), increases upon fullerene inclusion (e.g., O n-ary sumation I4 = 1.53 x 10-4 cm2 V-1 s-1 for C60 subset of(1a)2 and O n-ary sumation I4 = 1.45 x 10-4 cm2 V-1 s-1 for C70 subset of(1a)2 vs O n-ary sumation I4 = 2.49 x 10-5 cm2 V-1 s-1 for 1a) at 298 K. These findings provide support for the notion that controlling the nature of self-assembly supramolecular constructs formed from exTTF-porphyrin dimers through metalation or choice of fullerene can be used to regulate key functional features, including photoconductivity.

Automated summary

We reported the synthesis of a nanosized buckytrap, constructed from two bis-zinc(II) expanded-TTF (exTTF) porphyrin subunits, which could form discrete host-guest inclusion complexes with fullerenes. The axial ligands of the nanosized buckytrap determined the formation of either discrete complexes or infinite organic frameworks. Emission spectroscopic studies and flash-photolysis time-resolved microwave conductivity (FP-TRMC) studies revealed the binding stoichiometry and photoconductivity of the complexes.