Unclicking the Click: Metal-Assisted Mechanochemical Cycloreversion of Triazoles Is Possible

The Mechanism of Flex-Activation in Mechanophores Revealed By Quantum Chemistry

Flex-activated mechanophores can be used for small-molecule release in polymers under tension by rupture of covalent bonds that are orthogonal to the polymer main chain. Using static and dynamic quantum chemical methods, we here juxtapose three different mechanical deformation modes in flex-activated mechanophores (end-to-end stretching, direct pulling of the scissile bonds, bond angle bendings) with the aim of proposing ways to optimize the efficiency of flex-activation in experiments. It is found that end-to-end stretching, which is a traditional approach to activate mechanophores in polymers, does not trigger flex-activation, whereas direct pulling of the scissile bonds or displacement of adjacent bond angles are efficient methods to achieve this goal. Based on the structural, energetic and electronic effects responsible for these observations, we propose ways of weakening the scissile bonds experimentally to increase the efficiency of flex-activation.

Mechanochemistry in [6]Cycloparaphenylene: A Combined Raman Spectroscopy and Density Functional Theory Study

Raman spectroscopy under high pressures up to 10 GPa and density functional computations up to 30 GPa are combined to obtain insights into the behavior of a prototypical nanohoop conjugated molecule, [6]cycloparaphenylene ([6]CPP). Upon increasing pressure, the nanohoop undergoes deformations, first reversible ovalization and then at even higher pressures aggregates are formed. This irreversible aggregation is caused by the formation of new intermolecular σ-bonds. Frequencies and derivatives of the Raman frequency shifts as a function of pressure are well reproduced by the computations. The frequency behavior is tied to changes in aromatic/quinonoid character of the nanohoop. The modeling at moderate high pressures reveals the deformation of the [6]CPP molecules into oval-like and peanut-like shapes. Surprisingly the pressure derivatives of the observed Raman mode shifts undergo a sudden change around a pressure value that is common to all Raman modes, indicating an underlying geometrical change extended over the whole molecule that is interpreted by the computational modeling. Simulations predict that under even larger deformations caused by higher pressures, oligomerization reactions would be triggered. Our simulations demonstrate that these transformations would occur regardless of the solvent, however pressures at which they happen are influenced by solvent molecules encapsulated in the interior of the [6]CPP.