Engineering Ultrafast Molecular Rotors via Chalcogen bonds.

Chalcogen bonds are emerging σ-hole interactions with untapped potential in amphidynamic materials. We report the first crystalline molecular rotors held by chalcogen bonds and their ultrafast rotational dynamics. The rotator component 1,4-diazabicyclo[2.2.2]octane and phenylselenocyanate-based stators assemble via exceptionally short and highly directional Se···N contacts (Nc = 0.76-0.81; ∠NC-Se···N = 174-175 °). Solid-state 1H NMR T1 spin-lattice relaxation measurements reveal rotation at hundreds of MHz with low activation barriers (Ea = 1.22-2.78 kcal mol-1), in agreement with the packing coefficient and computational analysis. These findings highlight chalcogen bonds as a powerful tool for designing robust, crystalline molecular machines.