A Conjugated Thiophene-Based Rotaxane: Synthesis, Spectroscopy, and Modeling

A dithiophene rotaxane 1⊂β‐CD and its shape‐persistent corresponding dumbbell 1 were synthesized and fully characterized. 2D NOESY experiments, supported by molecular dynamics calculations, revealed a very mobile macrocycle (β‐CD). Steady‐state and time‐resolved photoluminescence experiments in solution were employed to elucidate the excited‐state dynamics for both systems and to explore the effect of cyclodextrin encapsulation. The photoluminescence (PL) spectrum of 1⊂β‐CD was found to be blueshifted with respect to the dumbbell 1 (2.81 and 2.78 eV, respectively). Additionally, in contrast to previous observations, neither PL spectra nor the decay kinetics of both threaded and unthreaded systems showed changes upon increasing the concentration or changing the polarity of the solutions, thereby providing evidence for a lack of tendency toward aggregation of the unthreaded backbone. A chemical workout: A dithiophene rotaxane and its reference dumbbell were synthesized by means of aqueous Suzuki coupling (see scheme). The structure of this encapsulated dithiophene was confirmed by 1D and 2D NMR spectroscopy as well as molecular dynamics calculations. Photophysical properties of both systems were also investigated.