Effects of micro-solvation on the reaction dynamics of biphenyl cations following hole capture

- The twist angle of the biphenyl radical cation (Bp+) vibrates strongly following hole capture.
- The friction of water molecules prevents the twist angle vibration of Bp+.
- The amplitude of the Bp+ twist vibration is decreased by water molecules.
- Hydration affects the proton-hyperfine coupling constants negligibly.

Biphenyl (Bp) and its related compounds are widely applied in single-molecule electronic devices. In this study, the effects of micro-solvation on the hole capture (ionization) dynamics of Bp were investigated by means of direct ab initio molecular dynamics (AIMD) simulations. The micro-solvation of Bp was simulated using one and two water molecules (i.e., Bp(H2O)n (n = 0-2)). The reaction dynamics of Bp+(H2O)n following hole capture were investigated via direct AIMD simulation. In the case without H2O (n = 0), the twist angle of Bp+ periodically vibrated without decay. In contrast, when water molecules were near Bp+, the amplitude of the twist angle vibration decayed periodically. The formation of hydrogen bonds between Bp+ and water molecules prevents periodic vibration by generating friction. The electronic states and reaction mechanism were investigated based on the theoretical results.

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