Unambiguous Determination of Electrostatically Driven Molecular Packing in a Triphenylene–Surfactant Complex Monolayer

Abstract

Emergence of ordered structures during molecular self‐assembly at interfaces is influenced by a variety of thermodynamic and kinetic factors that are not well understood. Experiments alone can only inform about the final architecture keeping self‐assembly pathways inaccessible. Here with the help of molecular dynamic simulations, the intricate details of the self‐assembly processes and resultant ordered structures of a triphenylene–surfactant complex monolayer at air–water interface are reported. The monolayer is observed to be stable and reversible using surface manometry and real‐time Brewster angle microscopy. Not only that the simulated isotherm and 2D density profiles are in good agreement with experimental observations, the simulation results bespeak the crucial role of specific electrostatic interactions forming the nanostructures at the interface analyzed via orientational structural profiles, radial distribution, and Z‐density profiles. Moreover, real‐space visualization using atomic force microscopy suggests that the molecular packing is preserved in the monolayer even after transferring onto a silicon substrate. Since the rational designing of organic electronics requires nanoscale control of molecular structures on solid substrates, it is anticipated that these results will be of fundamental importance.

Interaction Modes in Pressure-Induced Molecular Nanoarchitectonics of the Alkylated Azobenzene Monolayer: Interfacial Analyses and Molecular Dynamic Simulation

“…In the first case, negligible hysteresis was observed even after three cycles (Figure d), and film morphology showed similar cyclic changes (Figure S5b), suggesting the ability of the molecules to rearrange and reorient themselves depending on the available area so long as it is in the monolayer phase. For amphiphilic molecules, minimal hysteresis is observed when the molecule–water interactions dominate . In the second case, the area under compression–expansion showed a more significant difference in all three cycles (Figure S5a), and the π value at which bend in the isotherm occurred is considerably smaller in the third cycle than in the second and the first, indicating large hysteresis.…”

“…Because the simulation temperature is 300 K, the dynamics of the molecules are sufficiently fast for getting reasonably good statistical average with the above time scale. Analogous analysis time scales were formerly used in our previous simulation works where a good agreement with the experimental data was obtained. , …”

“…The water–alkylated azobenzene system was then compressed using the “on-the-fly” approach at a rate of 0.001 nm 2 /ps appreciably slow enough to avoid any perturbation in the system. Our previous work has observed that the rate does not remarkably perturb the system to an extent. From this trajectory, we extracted 13 different configurations with a surface area of 2.00, 1.60, 1.20, 1.00, 0.80, 0.70, 0.60, 0.58, 0.52, 0.50, 0.48, 0.46, and 0.40 nm 2 .…”

“…Despite several detailed experimental investigations on azo systems, the intricate details of molecular interactions at the air–water interface have not been probed with computer-based simulations, to the best of our knowledge, which can provide information on the dominant molecular interactions leading to stable films. Nonetheless, with the availability of models for many newly synthesized liquid crystals/surfactant molecules, , there are some reports on molecular dynamics (MD) simulations on them (but none of them contains azo). The dependence of the number of carbon atoms and double bonds in the hydrophobic tail region and the polarity of the aromatic core of liquid crystal molecules on the formation of thin films is understood from simulations.…”

Deciphering pressure-induced nanoarchitectonics in a monolayer of heterocoronene-based discotics at air–water and air–solid interfaces

“…For an amphiphilic molecule, where the molecule–water interaction dominates, minimal hysteresis is anticipated, as observed for TPC based DLC molecules. 37 However, for molecules with sufficiently strong intermolecular interactions, a tighter packing of the molecules during compression may result in a shifting of the isotherm to lower molecular areas. In addition, the isothermal displacement towards the π -axis after each iso-cycle may be a consequence of monolayer molecular loss, because the molecular area is calculated by assuming that all the molecules spread remain in the monolayer.…”