Multiguest-Induced Structural Switching in a Self-Assembled Monolayer Network at the Liquid-Solid Interface

One of the important aspects of self-assembled molecular networks (SAMNs) formed at the liquid-solid interfaces is the structural switching of SAMNs induced by external adsorbates, which serve as supramolecular guest molecules. However, guest-induced structural changes are not diverse, mostly switching from close-packed, nonporous patterns to porous patterns through an increase in the number and ordering of adsorbed alkyl chains of the stretched configuration accompanying few changes in the number of guest molecules. To achieve structural switching in response to multiguest molecules, we designed a building block DBA-DYN which has three alkyl chains. Each chain contains a stiff 1,3-butadiyne unit and a carbonyl group, imparting conformational dynamism and enabling hydrogen bonding, respectively. At the 1-phenyloctane-graphite interface, DBA-DYN forms closely packed networks in the absence of guests, with its alkyl chains adopting different conformations. In the presence of coronene (COR) used as a guest molecule, however, the SAMN structure transforms into a porous form comprising six DBA-DYN molecules in all-transoid geometry, where a large number of COR molecules are confined. Conversely, six molecules of triangular guest (DBA) are immobilized in a smaller space of the network formed by three DBA-DYN molecules in which alkyl chains are hydrogen-bonded, adopting an all-cisoid geometry. For the guest-dependent SAMN structure switching to occur, the carbonyl group of the diynone unit plays a crucial role through specific hydrogen bonds, both between DBA-DYN molecules and between DBA-DYN and COR guest molecules.