Minimum Energy Path Diffusion Monte Carlo Approach for Investigating Anharmonic Quantum Effects: Applications to the CH₃⁺ + H₂ Reaction

A method for evaluating anharmonic corrections to energies along a minimum energy path is developed and described. The approach is based upon the Diffusion Monte Carlo theory as initially developed by Anderson. Diffusion Monte Carlo has been shown to be effective for evaluating the ground-state properties of highly anharmonic systems. By using Jacobi coordinates, the evaluation of anharmonic corrections to the energies along a minimum energy path are straightforward to implement using Diffusion Monte Carlo. In this work, the CH₃⁺ + H₂ → CH₅⁺ reaction and its singly deuterated analogues are investigated. In addition to exploring how the energetics of this reaction change upon partial deuteration, projections of the probability amplitude onto various internal coordinates are evaluated and used to provide a quantum mechanical description of how deuteration affects the orientation of the two fragments as they combine to form the CH₄D⁺ molecular ion

Superstructures of Diketopyrrolopyrrole Donors and Perylenediimide Acceptors Formed by Hydrogen-Bonding and π···π Stacking

Synthetic supramolecular systems can provide insight into how complex biological systems organize as well as produce self-organized systems with functionality comparable to their biological counterparts. Herein, we study the assembly into superstructures of a system composed of diketopyrrolopyrrole (DPP) donors with chiral and achiral side chains that can form triple hydrogen bonds with perylene diimide (PDI) acceptors into superstructures. The homoaggregation of the individual components as well as the heteroaggregate formation, as a result of π···π stacking and H-bonding, were studied by variable-temperature UV/vis and CD spectroscopies and electronic structure theory calculations. It was found that, upon cooling, the achiral PDIs bind to disordered DPP stacks, which drives the formation of chiral superstructures. A new thermodynamic model was developed for this unprecedented assembly that is able to isolate the thermodynamic binding parameters (Δ<i>H</i>°, Δ<i>S</i>°) for all the different noncovalent contacts that drive the assembly. This novel assembly as well as the quantitative model described in this work may help researchers develop complex self-assembled systems with emergent properties that arise as a direct result of their supramolecular structures