Influence of Coulombic Interaction on the Interfacial Self-Assembly of Discotic Liquid Crystal Amphiphiles: A Combined Experimental and Computer Simulation Study

Abstract

Self-assembly of amphiphilic molecules largely depends on the structure and electronic properties of the polar head groups. An important class of amphiphiles with technological applications comprises the discotic liquid crystal (DLC) amphiphiles. Here, we report remarkable differences in the self-assembly properties of two similar discotic amphiphiles with dissimilar polar head groups, viz., imidazole-tethered with hexaalkoxytriphenylene (neutral-ImTp) and imidazolium-tethered with hexaalkoxytriphenylene (ionic-ImTp). Surface manometry reveals that the ionic-ImTp exhibits a larger limiting area, higher collapse pressure, and smaller compressional elastic modulus at the air−water interface as compared to the neutral-ImTp system. At the air−solid interface, ionic-ImTp can be transferred only up to a bilayer structure with undulated morphology, whereas the neutral-ImTp exhibits smooth morphology and higher transfer efficiency. These results are explained by density functional theory (DFT) calculations and molecular dynamics (MD) simulations, which elucidated that the Coulombic interaction is the dominant factor that controls the organization of these molecules. DFT calculations predicted a T-shaped π-stacking geometry for the ionic-ImTp and a parallel-displaced stacking geometry for the neutral-ImTp. MD simulation predicted the orientation of molecules and their strength of hydrogen bonding. Understanding the intermolecular interactions governing self-assembly is important to engineer molecular packing that controls the charge transport in DLCbased organic electronics.

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

“…To elucidate the phase transition and monolayer collapse with gradual compression, we calculate surface pressure–area isotherm using the method detailed elsewhere. [ 30,41,47,67 ] A semiquantitative agreement between the simulated and experimental isotherms is observed in Figure 5a. At 25 °C, a π c value of around 41 mN m −1 is reported in the experiment, and the simulated π c is around 30 mN m −1 .…”

“…A previous simulation study proved the efficacy of the OPLS/AA force field for predicting the structural properties of monolayer formed by similar liquid crystal molecules on the water surface. [ 30 ] The initial structures were built using the Packmol software. [ 39 ] About 11 head groups and 66 tail units (6 tails for each of the head group unit) were considered.…”

“…This closely followed the experimental approach. The previous simulation studies, [ 30,41 ] on the other hand, started from different surface areas without compressing the surface. Therefore, the present simulation method was more advanced and, therefore, had potential to provide more insights.…”

“…A recent study by Verma et al. [ 30 ] adopted similar simulation methodology analyzing the surface adsorption of neutral imidazole tethered with hexaalkoxytriphenylene (ImTp) and ionic ImTp. However, molecular dynamics (MD) simulation can also replicate the experimental way of gradual compression of the film and thereby reducing the surface area with time.…”

Controlled Growth and Self‐Assembly of Multiscale Organic Semiconductor

“…The scale of the assembled structure can be located in a range of nano/microscales to macroscales. [151][152][153][154] The output performance of multiscale OS assemblies is highly related to the structure and processing technology. However, the correlation between the morphology of the interfacial assembled system and the processing conditions is complicated.…”