Molecular dynamic simulation of polyhedral oligomeric silsesquioxane porphyrin molecules: Self-assembly and influence on morphology

Molecular dynamics was used to study the aggregation in water of three versions of polyhedral oligomeric silsesquioxane porphyrin (POSSP) molecules. The POSSP molecules have different functional groups; POSSP-IB has one hepta-isobutyl POSS unit, POSSP-Ph has one hepta-phenyl POSS molecule, and POSSP-TIB has four hepta-isobutyl POSS units. Three control porphyrins (TPP, ATPP, TATPP) were also simulated in this study. The effects of the different substituents on the POSSP aggregation process and final morphology were investigated. It is observed that the isobutyl substituents in the POSS units drives the aggregation mainly through the hydrophobic effect. In the case of the phenyl POSS unit, the self-assembly process is also carried through the hydrophobic effect, but pi-pi and H-bonding interactions play a role too. The final morphology of the aggregates show that the porphyrins associated with POSSP-IB and POSSP-TIB are far apart from each other contrary to POSSP-Ph, which may have a major implication on the optical properties of these aggregates. This study provides valuable insights on the aggregation in water of POSSP molecules, which are a tunable platform to design novel functional materials.