Dynamic Characterization of Crystalline Supramolecular Rotors Assembled through Halogen Bonding

A modular molecular kit for the preparation of crystalline molecular rotors was devised from a set of stators and rotators to gain simple access to a large number of structures with different dynamic performance and physical properties. In this paper, we have accomplished this with crystalline molecular rotors self-assembled by halogen bonding of di-azabicylo[2.2.2]octane (DABCO), acting as a rotator, and a set of five fluorine-substituted iodobenzenes that take the role of the stator. Using variable temperature 1H T1 spin lattice relaxation measurements, we have shown that all structures display ultrafast Brownian rotation with activation energies ranging from 2.4 to 4.9 kcal/mol and a pre-exponential factors of the order of 1-9 x 1012 s-1. Lineshape analysis of quadrupo-lar echo 2H NMR measurements in selected examples indicated rotational trajectories consistent with the 3-fold or 6 fold symmetric potential of the rotator.