Phosphorescence of 8-azasteroids and related compounds.
We have investigated the electron absorption, fluorescence and phosphorescence spectra of 8-azasteroids and model compounds containing enaminodicarbonyl fragment. It has been shown that the investigated compounds have absorption and phosphorescence spectra similar in form and position. The results obtained permit the conclusion that the main deactivation channel of the excited singlet state is the intersystem crossing. It is suggested that the investigated 8-azasteroids of enaminodicarbonyl series under light irradiation undergo phototransformations presumably into derivatives with a gamma-pyridone fragment.
Theoretical study of the phosphorescence of 8-azasteroids
We have used quantum chemical methods for a theoretical study of the luminescent characteristics (including estimating the rate constants for intramolecular T1 → S0 electronic transitions) of the molecules of four immunoactive compounds of the 8-azasteroid class. We have established that the T1 state is localized on the enaminodicarbonyl moiety that is common to all the molecules. We have shown that for the studied compounds, the phosphorescence spectra and the physical mechanisms for deactivation of the lower triplet state T1 are similar. For all the compounds, the results of the theoretical study are consistent with the corresponding conclusions of experimental studies of 8-azasteroids.
Refinement of crystal structure parameters using convergent‐beam electron diffraction: the low‐temperature phase of SrTiO3
The method to refine crystal structure parameters (atom positions and Debye–Waller factors) using convergent-beam electron diffraction (CBED), which is applicable to crystal structure analysis of a small specimen area down to a few nm in diameter, is studied. The line profiles of higher-order Laue-zone reflections are recorded using imaging plates. Theoretical intensities are calculated based on the dynamical theory of electron diffraction with the aid of the generalized Bethe approximation to shorten calculation time. The structural parameters are determined by fitting the experimental profiles with the theoretical ones using a nonlinear least-squares method. The present method has been applied to the low-temperature phase of SrTiO3. The structural parameter or the rotation angle of the oxygen octahedron has been determined to be \varphi = 1.12 (4)°, which shows good agreement with that obtained from electron spin resonance experiments.