Top: Scheme of a direct degradation process (DP). In average, the chromophores exposed to irradiation are excited to higher energy states with probability and decay with a probability to a state different from the original one. Bottom: Same scheme as on the top but through an indirect degradation process (IP) with a labile intermediate state.
Left: Structure of the DAT2 chromophore. Right: View of the DAT2 crystal structure along the axis that is lying on the film surface. The arrows represent the main charge transfer axis of the chromophores. They are slightly tilted toward the polar axis and span an angle of about 56° with the crystal plane , which corresponds to the film surface.
Absorption spectrum of 5% DAT2 hosted in the polymer APC for unpolarized light. The DAT2 chromophores show the same absorption characteristics also when mixed into PMMA or as single crystal. The resonant photoexcitation wavelength is also indicated in the figure.
Top: Photostability measurement for DAT2 in APC (red squares) and in PMMA (green rhombi) with the related theoretical curves according to the numerical model IP [Eqs. (3) and (4)], together with the first hour of DAT2 crystal irradiation (blue points) and the theoretical curve according to the numerical model DP [Eq. (2)]. Bottom: Crystalline DAT2 transmission for the -long bleaching experiment.
Change in transmission during the first of resonant irradiation of the chromophore DAT2 in an APC polymeric matrix, as presented in Fig. 4. The dashed (blue) line represents the approximated analytical fit of the data following Eq. (A1), while the solid (red) line represents the numerical fit of an indirect degradation process as described by the rate equation system [(3) and (4)].
Average number of photoexcitations without chromophore degradation along with the average absorption cross sections at for the two polymers APC and PMMA, doped with DAT2, and for the DAT2 crystal. Since the curve parameters are not completely orthogonal, the presented quantities have experimental incertitude of .
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