Semiconducting Supramolecular Organic Frameworks Assembled from a Near-Infrared Fluorescent Macrocyclic Probe and Fullerenes

We report here a
new extended tetrathiafulvalene (exTTF)-porphyrin
scaffold, 2, that acts as a ball-and-socket receptor
for C60 and C70. Supramolecular interactions
between 2 and these fullerenes serve to stabilize 3D
supramolecular organic frameworks (SOFs) in the solid state formally
comprising peapod-like linear assemblies. The SOFs prepared via self-assembly
in this way act as “tunable functional materials”, wherein
the complementary geometry of the components and the choice of fullerene
play crucial roles in defining the conductance properties. The highest
electrical conductivity (σ = 1.3 × 10–8 S cm–1 at 298 K) was observed in the case of the
C70-based SOF. In contrast, low conductivity was seen for
the SOF based on pristine 2 (σ = 5.9 × 10–11 S cm–1 at 298 K). The conductivity
seen for the C70-based SOF approaches that seen for other
TTF- and fullerene-based supramolecular materials despite the fact
that the present systems are metal-free and constructed entirely from
neutral building blocks. Transient absorption spectroscopic measurements
corroborated the formation of charge-transfer states (i.e., 2δ+/C60δ− and 2δ+/C70δ−, respectively) rather than fully charge separated states (i.e., 2•+/C60•– and 2•+/C70•–, respectively) both in solution (toluene and benzonitrile) and in
the solid state at 298 K. Such findings are considered consistent
with an ability to transfer charges effectively over long distances
within the present SOFs, rather than, for example, the formation of
energetically trapped ionic species.

本文报道了一种新型扩展型四硫富瓦烯（exTTF）-卟啉骨架化合物2，其可作为球窝受体，用于识别结合C60与C70。化合物2与上述富勒烯之间的超分子相互作用，可在固态下稳定形成形式上由豌豆荚状线性组装体构成的三维超分子有机框架（SOFs）。经该自组装方式制备的SOFs属于"可调谐功能材料"，组分间的互补几何结构与富勒烯的选择，对其导电性能的调控起到关键作用。在298 K条件下，基于C70的SOFs展现出最高电导率（σ = 1.3 × 10–8 S cm–1）；与之相对，纯化合物2制备的SOFs电导率极低（σ = 5.9 × 10–11 S cm–1，298 K）。尽管本研究体系为无金属且完全由中性结构单元构建，基于C70的SOFs的电导率仍可媲美其他基于四硫富瓦烯（TTF）与富勒烯的超分子材料。瞬态吸收光谱测试证实，在298 K下的溶液（甲苯与苯甲腈）及固态体系中，均形成了电荷转移态（分别为2δ+/C60δ−与2δ+/C70δ−）而非完全电荷分离态（分别为2•+/C60•–与2•+/C70•–）。上述结果与本研究SOFs内部可实现长距离有效电荷转移的结论相符，而非形成诸如能量俘获的离子物种。