Self-Assembled Perylene Bisimide-Cored Trigonal Prism as an Electron-Deficient Host for C60 and C70 Driven by "Like Dissolves Like".

Poor processability of fullerenes is a major remaining drawback for them to be studied monomolecularly and to find real-life applications. One of the strategies to tackle this problem is to encapsulate them within a host, which is however quite often, accompanied by significant alteration of their physical/chemical properties as encountered in chemical modification. To minimize the effect, an electron-deficient entities-based, dissolvable, and fluorescence active supramolecular host was designed and constructed via coordination-driven self-assembly of o-tetrapyridyl perylene bisimide (PBI) with cis-(PEt3)2Pt(OTf)2. The trigonal prism 1 possesses a trigonal-prismatic inner cavity with 14.7 Å as the diameter of its inscribed circle. Host-guest chemistry investigations revealed that both C60 and C70 could be quantitatively encapsulated by the host in a 1:1 ratio. Further studies demonstrated that the produced host-guest complex 1⊃C70 is significantly more stable than 1⊃C60, allowing complete transformation of the latter to the former and separation of C70 from its mixture with C60. The fullerenes in the inclusion state could rotate freely within the cavity. Electrochemistry and spectroscopy studies disclosed that the encapsulation of the guests shows little effect upon the reduction of the host and its fluorescence properties. Thus, "like dissolves like" is believed to be the main driving force for the formation of the host-guest complexes. Moreover, the host and host-guest complexes can be fabricated into monomolecular membranes using the conventional Langmuir-Blodgett technique. We propose that these unique host-guest complexes could be used as model ensembles for further studies of the physical/chemical properties of fullerenes in both single molecular and 2D membrane states. In addition, their reversible four-electron reduction property may allow them to find applications in photo/electrocatalysis, organic electronics, etc.