The single life: The reaction of [PhC(NtBu)2]SiCl3 (1) with potassium afforded the monomeric chlorosilylene [PhC(NtBu)2]SiCl (2). The X‐ray crystal structure of 2 has been determined and natural‐bond‐orbital analysis carried out.

The so-called S* state has been suggested to play an important role in the photophysics of beta-carotene and other carotenoids in solution and photosynthetic light-harvesting complexes, yet its origin has remained elusive. The present experiments employing temperature-dependent steady-state absorption spectroscopy and ultrafast pump-supercontinuum probe (PSCP) transient absorption measurements of beta-carotene in solution demonstrate that the spectral features of S* are due to vibrationally excited molecules in the ground electronic state S(0). Characteristic spectral signatures, such as a highly structured bleach below 500 nm and absorption in the range 500-660 nm result from the superposition of hot S(0) absorption ("S(0)*") on top of the ground-state bleach of room-temperature molecules. Appearance and disappearance of the S(0)* molecules can be completely described by a global kinetic analysis employing time-dependent species-associated spectra without the need to invoke the population of an intermediate electronically excited state.

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Das Singleleben: Bei der Reaktion von [PhC(NtBu)2]SiCl3 (1) mit Kalium entsteht das monomere Chlorsilylen 2. An dieser Verbindung wurden eine Röntgenstrukturanalyse und eine Natural‐Bond‐Orbital‐Analyse durchgeführt.

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.