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, H 2 O 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 C 70 . 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• C 60 ) n or ( 2 •C 70 ) n . This difference is ascribed to the fact that in 1a and 1b the axial positions are blocked by a H 2 O or THF ligand. Emission spectroscopic studies supported a 1:1 host–guest binding stoichiometry, allowing association constants of (2.0 ± 0.5) × 10 4 M –1 and (4.3 ± 0.9) × 10 4 M –1 to be calculated for C 60 and C 70, 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 (ϕ∑μ), increases upon fullerene inclusion (e.g., ϕ∑μ = 1.53 × 10 –4 cm 2 V –1 s –1 for C 60 ⊂( 1a ) 2 and ϕ∑μ = 1.45 × 10 –4 cm 2 V –1 s –1 for C 70 ⊂( 1a ) 2 vs ϕ∑μ = 2.49 × 10 –5 cm 2 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.