Conformational Polymorphism and Phase Coexistence in Interfacial Self-Assembly of V-Shaped Thienophenanthrene...

Two-dimensional supramolecular self-assembly at solid-liquid interfaces is governed by molecular conformation, intermolecular interactions, solvent environment, and solution concentration. Here, scanning tunneling microscopy and density functional theory calculations are employed to investigate the self-assembly of two V-shaped thienophenanthrene derivatives, TENTD-14 and TENTD-16. Each molecule adopts three conformations differentiated by the outward/inward orientation of naphthalene moieties: one naphthalene unit pointing outward, two naphthalene units pointing outward, and two naphthalene units folding inward. At high concentration in polar 1-octanoic acid, TENTD-14 assembles into zigzag stripes mainly constructed by the first two conformations, which are stabilized by four distinct hydrogen-bonding configurations consisting of O-H···O═C and O-H···π interactions. Upon dilution, TENTD-14 maintains the zigzag arrangement and simultaneously forms dendritic networks solely composed of the two-outward-naphthalene conformation. At high concentration, TENTD-16 also yields zigzag stripes incorporating all three conformers via a hydrogen-bonding scheme with three unique hydrogen-bond motifs. Decreasing the solution concentration, the zigzag packing remains dominant for TENTD-16, accompanied by flower-like aggregates exclusively built from the two-inward-naphthalene conformation stabilized by cyclic O-H···O═C hydrogen bonds. In nonpolar pentadecane, TENTD-16 forms a dendritic structure only consisting of the single-outward-naphthalene conformation, driven by van der Waals forces and solvent coadsorption. These results demonstrate that solvent polarity and alkyl-chain length jointly regulate conformational selection and tailor diverse supramolecular packing architectures.