Pressure-Induced Conformation Transition of o-Phenylene Solvated in Bulk Hydrocarbons

M Riello and G Doni and SV Filip and M Gold and A De Vita, JOURNAL OF PHYSICAL CHEMISTRY B, 118, 13689-13696 (2014).

DOI: 10.1021/jp5096272

The conformational behavior of o-phenylene 8-mers and 10-mers solvated in a series of linear alkane solvents by means of classical molecular dynamics and first-principles calculations was studied. Irrespective of the solvent used, we find that at ambient pressure the molecule sits in the well-defined close-helical arrangement previously observed in light polar solvents. However, for pressures greater than 50 atm, and for tetradecane or larger solvent molecules, our simulations predict that o-phenylene undergoes a conformational transition to an uncoiled, extended geometry with a 35% longer head-to-tail distance and a much larger overlap between its lateral aromatic ring groups. The free energy barrier for the transition was studied as a function of pressure and temperature for both solute molecules in butane and hexadecane. Gas- phase density functional theory-based nudged elastic band calculations on 8-mer and 10-mer o-phenylene were used to estimate how the pressure- induced transition energy barrier changes with solute length. Our results indicate that a sufficiently large solvent molecule size is the key factor enabling a configuration transition upon pressure changes and that longer solute molecules associate with higher conformation transition energy barriers. This suggests the possibility of designing systems in which a solute molecule can be selectively activated by a controlled conformation transition achieved at a predefined set of pressure and temperature conditions.

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