Regulating Rotational Dynamics of Co-Adsorbed Guest Molecules via Halogen Bonds in Functionalized Pores of Self-Assembled Molecular Networks at the Liquid-Solid Interface.

Understanding and controlling molecular rotation on surfaces is crucial for the development of molecular-scale artificial motors that operate at interfaces. Herein, it is reported the successful co-adsorption of guest molecules within the functionalized 2D pores of self-assembled molecular networks (SAMNs) through directional halogen bonding, as confirmed by scanning tunneling microscopy. Specifically, the porous SAMN formed by dehydrobenzo[12]annulene derivative DBA-Py with a pyridyl group at the termini of its three alkoxy chains, hosts an iodinated trigonal guest molecule, tris(4-iodophenyl)benzene (TIB), through a halogen bond between the nitrogen and iodine atoms. Within the pores, the TIB molecule exhibits rotational motion, preferentially residing at two locations. In contrast, within the pores formed by a mixture of DBA-Py and DBA-Ph, where DBA-Ph features three phenyl groups instead of pyridyl groups, the guest molecule preferentially resides in a single location. This behavior is attributed to the reduced number of energy minima within the pores owing to the decreased number of pyridyl units. Statistical analysis of the guest orientation suggests that the on-surface arrangement of DBA-Py and DBA-Ph is influenced by the guest molecule. This modular approach using functionalized pores in SAMNs provides an effective strategy for controlling molecular rotational behavior.