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Single-molecule imaging and manipulation with optical microscopy have become essential methods for studying biomolecular machines; however, only few efforts have been directed towards synthetic molecular machines. Single-molecule optical microscopy was now applied to a synthetic molecular rotor, a double-decker porphyrin (DD). By attaching a magnetic bead (ca. 200 nm) to the DD, its rotational dynamics were captured with a time resolution of 0.5 ms. DD showed rotational diffusion with 90° steps, which is consistent with its four-fold structural symmetry. Kinetic analysis revealed the first-order kinetics of the 90° step with a rate constant of 2.8 s−1. The barrier height of the rotational potential was estimated to be greater than 7.4 kJ mol−1 at 298 K. The DD was also forcibly rotated with magnetic tweezers, and again, four stable pausing angles that are separated by 90° were observed. These results demonstrate the potency of single-molecule optical microscopy for the elucidation of elementary properties of synthetic molecular machines. [ABSTRACT FROM AUTHOR]

Der Gast bestimmt: Ein Porphyrinpolymer, poly(PorZn⋅DD) (siehe Bild, rosa/violett), mit einem Porphyrinatozink ‐ und einem Porphyrin ‐ Doppeldeckerkomplex als Wiederholungseinheit, wurde synthetisiert. Die Porphyrinatozinkkomplexe in ihm erkennen ein divalentes Amin (braun/rot), was eine intramolekulare Drehbewegung durch Rotation der Porphyrin ‐ Doppeldeckerkomplexe zur Folge hat und so zu einer Verkürzung und Kompaktierung des Polymers führt. [ABSTRACT FROM AUTHOR]