Self-Assembly of Isomeric Isosceles Triangle Molecules at the Liquid–Solid Interface

We report the formation of self-assembled molecular networks (SAMNs) by isomeric isosceles triangle molecules, dehydrobenzo[14]annulene ([14]DBA), and dehydrobenzo[15]annulene ([15]DBA) derivatives bearing six decyloxy chains, at the 1-phenyloctane (PO)–graphite interface as investigated by scanning tunneling microscopy (STM). [15]DBA produces a Trimer+Tetramer structure with a surprisingly large unit cell comprising 12 independent [15]DBA molecules. In contrast, [14]DBA forms a simple Dimer structure consisting of two [14]DBA molecules per unit cell. The lowest solute concentrations for SAMN formation are 2 × 10–6 mol/L and 1 × 10–5 mol/L for [14]DBA and [15]DBA, respectively, differing by approximately a factor of 5. Thus, even a slight modification of the triangular core shape leads to significant differences in their self-assembly behavior. Molecular mechanics (MM) simulations suggest that these differences arise, at least in part, from differences in intermolecular and molecule–substrate interactions in SAMNs. Finally, mixing the constitutional isomers results in the formation of a regular coassembly, namely a Dimer+Dimer structure. The relative stabilities of the three structures are discussed based on experimental observations and nonbonding interactions estimated by MM simulations. This fundamental information is useful for advancing two-dimensional crystal engineering at the interface.