Noncovalent Interactions Governing Self‐Assembly of Oligomeric Phenolic Surfactant Film Models

ABSTRACT Self‐assembly of surfactants at interfaces and the structures formed are governed by complex sets of noncovalent interactions. This is exemplified in monolayers of phenolic surfactants, for example, dipalmitoylgalloylglycerol and octadecylgallate, at the air‐water interface, that show unusual cohesive properties and a high degree of self‐organization. The specific noncovalent interactions responsible for this behaviour are difficult to determine with experimental methods alone, which limits the rational design of phenolic thin film structures. Herein, trimers of gallate surfactant analogues have been investigated by computational methods, using ωB97X‐D/6‐31+G(d,p)//GFN1‐xTB. Analogues varied in their tail length (methyl, ethyl or butyl), the presence of the ester moiety and the presence of hydroxy groups meta to the tail. Two arrangements were studied for each trimer: a cyclic cone arrangement, similar to that observed with phenol, and a stacked 2 + 1 π arrangement. Each trimer was studied in the gas phase and implicit water solvent, using the GBSA model. The 2 + 1 π arrangement is more energetically favourable than the cyclic cone arrangement when ester and/or meta hydroxy groups are introduced, despite its lack of O‐H…O interactions between para hydroxy groups. In trihydroxy esters, C‐H…O interactions between the ester groups and O‐H…O interactions between meta hydroxy groups drive the 2 + 1 π formation. The degree of ring–ring overlap is dictated by the presence of the ester group, highlighting the role of the headgroup‐tail linker group. This study lays the groundwork for an understanding of the self‐assembly and behaviour of gallate surfactant monolayers at the molecular level.