The addition of p-perfluoro-ethylbenzoic acid as capping reagent yields stable size-selected MOF-5 colloids and suggests a general concept for controlled particle formation of carboxylic acid based MOFs in solution.

Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

The light-induced (266 nm) ultrafast decarboxylation of two peroxides R 1 -C(O)O-OR 2 , with R 1 ) phenyl and R 2 ) benzoyl or tert-butyl, in solution has been studied on the picosecond time scale by absorption spectroscopy with a time resolution typically of 100 to 200 fs. The reaction was investigated in various solvents of different polarity and viscosity to elucidate the influence of the solvent environment on the decarboxylation rate. Transient intermediate benzoyloxy radicals, R 1 -CO 2 , were monitored at wavelengths between 300 and 1000 nm. While the primary dissociation of the peroxide is too fast to be resolved, the dissociation of intermediate benzoyloxy radicals is clearly detected on the picosecond time scale. The mechanism of light-induced two-step dissociation is discussed, as is the dependence of reaction dynamics on the type of substituent R 2 as well as the branching ratio between prompt and delayed CO 2 formation. A model for the decarboxylation process is presented that is based on molecular structure parameters and energies. The latter quantities, which are obtained from density functional theory calculations, serve as input data for calculations of the specific decomposition rate coefficients of benzoyloxy intermediates via statistical unimolecular rate theory. The predicted benzoyloxy radical decay data are compared with corresponding experimental concentration versus time traces.

To achieve large population transfer to high vibrational levels in a selected ground-state mode of a polyatomic molecule [Cr(CO)6], we apply chirped femtosecond mid-infrared laser pulses at 2000 cm−1 to optimize vibrational ladder climbing as an energy deposition mechanism, which in turn controls the outcome of a unimolecular dissociation process. Its dependence on excitation parameters (frequency, intensity, chirp) is investigated and found to be in excellent agreement with a theoretical calculation. In particular, it is shown that optimizing vibrational ladder climbing allows for coherently controlled excitation even in a polyatomic molecule.