Fluorescence lifetime imaging (FLIM) is aiming at the measurement of molecular parameters in the local environment of the fluorophores. It exploits the fact that the fluorescence decay function of a fluorophore depends on its molecular environment but not on the fluorophore concentration. A fluorescence lifetime imaging (FLIM) technique for application in biology has to combine high photon efficiency, high lifetime accuracy, resolution of multi-exponential decay profiles, simultaneous recording in several wavelength intervals, high spatial resolution, and suppression of out-of-focus fluorescence and scattered light. We will show that the combination of multidimensional time-correlated single-photon counting (TCSPC) with confocal or multiphoton laser scanning meets these requirements almost ideally. FLIM by multidimensional TCSPC is based on scanning the sample by a high repetition rate pulsed laser beam and the detection of single photons of the fluorescence signal returning from the sample. In the simplest case, each photon is characterized by its time in the laser pulse period and the coordinates of the laser spot in the scanning area in the moment of its detection. The recording process builds up a photon distribution over these parameters. The result is an array of pixels, each containing a full fluorescence decay curve in a large number of time channels. TCSPC-FLIMhas got a new push from the introduction of 64-bit data acquisition software. Due to the large memory space available in the 64-bit environment FLIMcan now be recorded at unprecedented pixel numbers. This allows a large number of cells to be imaged simultaneously under identical experimental conditions. The technique can further be extended by including additional parameters in the photon distributions. Such parameters can be the wavelength of the photons, additional spatial coordinates, the time after a stimulation of the sample, or the time within the period of an additional modulation of the laser. These advanced techniques can be used to record lateral mosaics of FLIM images, FLIM Z-stacks, multiwavelength FLIM images, images of physiological effects occurring in the sample, and to simultaneously record fluorescence and phosphorescence lifetime images.
Europium Hexathiohypodiphosphate Eu2P2S6 with Eu in the oxidation state 2 has been prepared by direct elemental synthesis at high temperatures. Its vibrational spectrum has been recorded. The observed frequencies are assigned on the basis of P2S64- units with C2h symmetry in the crystal in analogy to Sn2P2S6 (monoclinic modification II).
Raman spectra of molten Tl2P2S2 and of Alkali bromide-Tl2P2S6 melt mixtures have been recorded. The spectra are interpreted from the temperature dependent dimer-monomer equilibrium P2S2-6 ⇄ 2 PS-3. We propose the planar structure [xxx] (D3h symmetry) with delocalization of charge for the uncommon PS-3 anion. It is pointed to an analogy of P2S2-6 and the isoelectronic Al2Cl6. Lewis acid-base equilibria are formulated for molten Me2S-phosphorus sulfide systems.