Recent successes in covalent polymer mechanochemistry might more easily be translated to stress-responsive bulk materials if easily scalable and minimalist mechanophores were identified. Epoxides represent attractive modifications of unsaturated polymer backbones for this purpose, but they suffer from limited mechanical reactivity. Here, we report that placing alkenes adjacent to cis-epoxide mechanophores along a polymer backbone results in ring-opening to carbonyl ylides during sonication, whereas epoxides with an adjacent saturated, linear alkyl chain do not. Upon release, tension-trapped ylides preferentially close to their trans-epoxides in accordance with the Woodward–Hoffmann rules. The reactivity of carbonyl ylides is exploited to tag the activated species with spectroscopic labels and to facilitate force-induced cross-linking through a reaction with pendant alcohols on co-polymers. The alkene effect is attributed to a combination of lower activation energy of the reaction (ΔG ‡) and greater force-coupled change in the length as the reaction proceeds from the ground to transition state (Δx ‡) relative to epoxides without the alkene. Even with alkene assistance, mechanochemical reactivity remains low; single-molecule force spectroscopy establishes that at  ∼2500 pN  ring-opening  proceeds with a rate constant that is less than approximately 5 s–1 in toluene.

Vibrational energy redistribution after selective excitation in nitromethane was simulated by ab initio molecular dynamics which could be directly compared with the 3D IR-Raman spectra, and provide more information of the internal mechanism.

Ab initio molecular dynamics simulations are presented to investigate the intramolecular vibrational energy redistribution (IVR) of an isolated nitromethane molecule. A number of IVR processes are simulated by monitoring the kinetic energy of vibrational modes under selective low-lying vibrational excitations from their ground states (Δν = 1 or 2). Evolution of the normal-mode kinetic energy gives the ultrafast energy transfer processes from parent modes to daughter modes intuitively. From the ultrafast vibrational transfer made by Fourier transformation of the time-dependent normal-mode kinetic energy, we can capture that the symmetry of the normal modes plays an important role in the anharmonic coupling between the vibrational modes. The results show three symmetry-dependent coupling mechanisms: direct symmetric coupling, overtone-assisted coupling, and rotation-assisted coupling. Furthermore, the calculated efficiencies of IVR also coincide with these mechanisms.

Semiconductor quantum dots (QDs) are widely used in light-emitting diodes and solar cells. Electrochemical modulation is a good way to understand the electrical and optical properties of QDs. In this work, the effects of electrochemical control on photoluminescence (PL) spectra in core/shell CdSe/ZnS QD films are studied. The results show different spectral responses for surface emission and core emission when a negative electrochemical potential is applied: the core emission is redshifted while the surface emission is blueshifted. The former is attributed to the electrostatic expansion of the excitonic wave function, due to the asymmetric distribution of adsorbed cations on the surface of the dots. The latter is attributed to the occupation of lower surface states by the injected electrons, i.e., the photoexcited electrons are more likely to be trapped onto higher surface states, leading to a blueshift of the surface emission. Both the spectral shift and the accompanying PL-quenching processes are reversible by resetting the potential.