The reversible switching of a water-soluble spiropyran compound is recorded over 1 ns by means of femtosecond vis-pump/vis- and IR-probe spectroscopy under aqueous conditions. Our investigations reveal that the photochemical conversion from the closed spiropyran to the open merocyanine takes 1.6 ps whereas the reversed photoreaction is accomplished within 25 ps. The combination of time-resolved and steady-state observations allows us to reveal central parts of the reaction pathway leading to either form. The enhanced water solubility, its fast and efficient switching behavior, and its stability against hydrolysis over a time range of several weeks make this compound an attractive and versatile tool for biological applications.

The ultrafast photochemistry of a new spiropyran photoswitch (Py-BIPS) has been investigated, revealing many advantages in the application in water over the previously studied spiropyrans. Functionalized Py-BIPS derivatives are presented for the study of pH dependence, stability, toxicity, and the thermal and photochemical behavior on longer time scales in aqueous media using several spectroscopic methods. These investigations pave the way for the practical use of Py-BIPS derivatives as photoswitchable ligands of biomolecules.

The cleavage of a photolabile nitroveratryloxycarbonyl protecting group, which is widely used as caging group, was studied by femtosecond transient absorption spectroscopy in the visible and infrared spectral range and by flash-photolysis experiments on the longer time scale. On the basis of quantum-chemical calculations it is shown that directly after excitation, triplet absorption that is not part of the reactive pathway dominates the transient spectrum and that the molecules following the triplet pathway are trapped in a nonreactive triplet state. By contrast, photolysis proceeds from the singlet manifold. Therefore, trapping in the triplet state lowers the quantum yield of the process for this compound compared with other o-nitrobenzyl protecting groups. With our integrated approach of time-resolved UV and IR measurements and calculations, we can characterize the entire uncaging mechanism and identify the most relevant intermediate states along the reaction pathway. The final uncaging is accomplished within 32 μs.

The antibiotic puromycin, which inhibits protein translation, is used in a broad range of biochemical applications. The synthesis, characterization, and biological applications of NVOC-puromycin, a photocaged derivative that is activated by UV illumination, are presented. The caged compound had no effect either on prokaryotic or eukaryotic translation or on the viability of HEK 293 cells. Furthermore, no significant release of ribosome-bound polypeptide chains was detected in vitro. Upon illumination, cytotoxic activity, in vitro translation inhibition, and polypeptide release triggered by the uncaging of NVOC-puromycin were equivalent to those of the commercial compound. The quantum yield of photolysis was determined to be 1.1 AE 0.2 % and the NVOCpuromycin was applied to the detection of newly translated proteins with remarkable spatiotemporal resolution by using two-photon laser excitation, puromycin immunohistochemistry, and imaging in rat hippocampal neurons.

We present supercontinua generated in LiF and CaF(2) revealing that LiF is advantageous especially in the near UV region since it pushes the cut-off wavelength about 17 nm towards lower wavelengths and the occurrence of color centers, which has been considered as a drawback up to now, is not a limitation for its applicability in femtosecond transient absorption spectroscopy. Even though the color centers occur within a short time of illumination, they do not influence the supercontinuum generation significantly and they can furthermore, if desired, be eliminated from the substrate simply by heating. Thus LiF is a promising substrate for broad band measurements in the UV/vis range.