1. What is “Covalent Mechanochemistry” ? 5412 2. From Macroscopic Milling to Bond-Selective Manipulation 5415 2.

Covalent mechanochemistry: theoretical concepts and computational tools with applications to molecular nanomechanics.

The recently proposed rSCAN functional [ J. Chem. Phys. 2019 150, 161101] is a regularized form of the SCAN functional [ Phys. Rev. Lett. 2015 115, 036402] that improves SCAN’s numerical performanc...

Accurate and Numerically Efficient r2SCAN Meta-Generalized Gradient Approximation.

Polymer mechanochemistry can trigger a wide range of often unanticipated reactivity, but the focus of these systems typically falls on the structure of the mechanophore rather than the intervening polymer backbone. Now, it has been shown that a poly(norbornene) backbone has a substantial impact on a mechanochemical ring-opening reaction, despite having only a minor effect on the force-free reaction.

A backbone lever-arm effect enhances polymer mechanochemistry

Ultrasound activation of mechanophores embedded in polymer backbones has been extensively studied of late as a method for realizing chemical reactions using force. To date, however, there have been few attempts at systematically investigating the effects of mechanophore structure upon rates of activation by an acoustic field. Herein, we develop a method for comparing the relative reactivities of various cyclobutane mechanophores. Through the synthesis and ultrasonic irradiation of a molecular weight series of poly(methyl acrylate) polymers in which each macromolecule has a single chain-centered mechanophore, we find measurable and statistically significant shifts in molecular weight thresholds for mechanochemical activation that depend on the structure of the mechanophore. We also show that calculations based on the constrained geometries simulate external force method reliably predict the trends in mechanophore reactivity. These straightforward calculations and the experimental methods described herein m...

Structure–Mechanochemical Activity Relationships for Cyclobutane Mechanophores

Transformation of naphthopyran into a colored merocyanine species in polymeric materials is achieved using mechanical force. We demonstrate that the mechanochemical reactivity of naphthopyran is critically dependent on the regiochemistry, with only one particular substitution pattern leading to successful mechanochemical activation. Two alternative regioisomers with different polymer attachment points are demonstrated to be mechanochemically inactive. This trend in reactivity is accurately predicted by DFT calculations, reinforcing predictive capabilities in mechanochemical systems. We rationalize the reactivity differences between naphthopyran regioisomers in terms of the alignment of the target C–O pyran bond with the direction of the applied mechanical force and its effect on mechanochemical transduction along the reaction coordinate.

Regioisomer-Specific Mechanochromism of Naphthopyran in Polymeric Materials.

TURBOMOLE is a collaborative, multi-national software development project aiming to provide highly efficient and stable computational tools for quantum chemical simulations of molecules, clusters, periodic systems, and solutions. The TURBOMOLE software suite is optimized for widely available, inexpensive, and resource-efficient hardware such as multi-core workstations and small computer clusters. TURBOMOLE specializes in electronic structure methods with outstanding accuracy-cost ratio, such as density functional theory including local hybrids and the random phase approximation (RPA), GW-Bethe-Salpeter methods, second-order Moller-Plesset theory, and explicitly correlated coupled-cluster methods. TURBOMOLE is based on Gaussian basis sets and has been pivotal for the development of many fast and low-scaling algorithms in the past three decades, such as integral-direct methods, fast multipole methods, the resolution-of-the-identity approximation, imaginary frequency integration, Laplace transform, and pair natural orbital methods. This review focuses on recent additions to TURBOMOLE's functionality, including excited-state methods, RPA and Green's function methods, relativistic approaches, high-order molecular properties, solvation effects, and periodic systems. A variety of illustrative applications along with accuracy and timing data are discussed. Moreover, available interfaces to users as well as other software are summarized. TURBOMOLE's current licensing, distribution, and support model are discussed, and an overview of TURBOMOLE's development workflow is provided. Challenges such as communication and outreach, software infrastructure, and funding are highlighted.

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TURBOMOLE: Modular program suite for ab initio quantum-chemical and condensed-matter simulations

The role played by polyethylene-like oligomers in transducing external tensile forces to benzocyclobutene mechanophores is investigated computationally. It is demonstrated that the oligomer chains do indeed exert a notable influence on the force dependence of the activation energies of both conrotatory and disrotatory ring-opening processes of a cis 1,2-disubstituted benzocyclobutene. This opens the doorway to tuning the properties of mechanoresponsive materials not only by changing the properties of the mechanophore itself, but also by tailoring the force-transducing chain molecules attached to it. Furthermore, it is found that these chains even have a profound impact on the topology of the force-transformed potential energy surface in the vicinity of conrotatory transition states. Hitherto unexpected and most striking is the phenomenon that some of these conrotatory transition states are found to drive the system to disrotatory products.

Matthias Rückert

Papers

TURBOMOLE: Modular program suite for ab initio quantum-chemical and condensed-matter simulations

On the role of polymer chains in transducing external mechanical forces to benzocyclobutene mechanophores