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

Beyond explaining scientific curiosity, molecular self-assembly is an essential tool for the controlled fabrication of nanoscale devices with the desired functionalities. Molecules containing azo groups are potential candidates for photoswitchable optoelectronic applications. Herein, we synthesized an alkylated azobenzene (AAB) molecule and studied its interfacial self-assembly by surface manometry and molecular dynamics (MD) simulation. The alkylated azobenzene molecules form a stable and reversible monolayer at the air–water interface. The monolayer phase transforms from a liquid expanded (LE) to liquid condensed (LC) phase upon compression, as observed by surface pressure (π)–area per molecule (A) and surface potential (ΔV)–A isotherms and Brewster angle microscopy (BAM). Using MD simulation, the resultant molecular ordering is analyzed via orientational structural profiles, spatial and radial distributions, order parameters, and densmap profiles. Not only the simulated isotherm corroborated the experimental observations, but the MD simulation also revealed that the number of hydrogen bonds in the molecule–molecule interaction dominates over the molecule–water interaction in the LC phase. However, a perfectly ordered alignment of tail groups is not seen due to the hindrance between the head groups featured by the diazo benzene group. This study elucidates the molecular interactions controlling the self-assembly responsible for forming a stable monolayer at the air–water interface.