Molecular Hinges by Fusion of Pyrrole and Dithiin: Synthesis, Structure, Redox Chemistry and Host-Guest Complexation of Dipyrrolo-1,4-dithiins.

Abstract

A series of novel hinge-like molecules, namely dipyrrolo-1,4-dithiins (PDs), were prepared and fully characterized by NMR, UV/vis, cyclic voltammogram, ESR, and single crystal X-ray diffraction (SCXRD) analysis. The lateral fusion of pyrroles with 1,4-dithiins has led to not only retained key features of a dithiin, but also enhanced redox-activity with increased susceptibility to radical cations via redox or chemical oxidation. Stabilization of their radicals are observed for the N,N-tert-butyl or N,N-triphenylmethyl PD as evidenced by ESR measurements. DFT calculations and SCXRD analysis revealed PDs are extremely flexible with adaptive molecular geometries that can be mechanically regulated via crystal packing or host-guest complexation. The excellent donor nature of PDs renders inclusion complexes with the cyclophane bluebox (cyclobis(paraquat-p-phenylene)), featuring association constants up to 104 M-1 . Additionally, a planarized transition intermediate associated with inversion dynamics of a PD has been preserved in the pseudorotaxane structure with assistances of π⋅⋅⋅π and S⋅⋅⋅π interactions. The hinged structure, excellent redox-activity, and adaptive nature of PDs could further enable accesses to exotic redox switchable host-guest chemistry and functional materials.