STM Exploration of the Diverse Polymorphs for Tri‐Substituted Anthraquinone Derivatives via Alkyl Chain Elongation

Fabrication of structural diversity in self‐assembled monolayers has gained considerable attention, not only due to its significance in interface science but also because of its potential application in designing nanomaterials. Here, systematical characterization of the molecular self‐assembly of tri‐substituted anthraquinone derivatives at the 1‐octanoic acid/HOPG interface is provided. Different nanopatterns of Linear I, Butterfly‐like, and Linear II are recorded for 1,2,4‐A‐3OC₁₆ by gradually changing the solution concentration. Diverse polymorphs are also obtained by alkyl chain elongation, meaning that 1,2,4‐A‐3OC_15,17,18 adopt Dimer‐Linear, Linear III, and Linear IV structures, respectively. Dipole–dipole, hydrogen bonding, and van der Waals interactions are the dominant forces on forming the stable adlayers. Also, the coadsorption of the solvent molecules is a common phenomenon, ascribing to space matching and gain of enthalpy. Moreover, the 1,2,4‐A‐3OC_17,18 self‐assembled into monolayers consists of both ordered and chaotic domains. This loss of regularity is attributed to the large number and long length of the side chains, for entropy reasons. This work provides important insight into the fabrication of complex molecular self‐assembly and the exploration of monolayers at the liquid/solid interface.