Laser photolysis of complexes of etioporphyrin I with rare-Earth elements

Abstract

gate nonluminescent complexes also. We undertook an investigation of the spectra and kinetics of induced absorption in complexes of porphyrins with rare-earth elements with a nanosecond laser-photolysis unit. In the present communication, we present the results of an investigation of rare-earth complexes of etioporphyrin I. Excitation was carried out with the second harmonic of an LTI PCh-7 neodymium laser. A DKSSh-150 xenon lamp in a pulsed mode was used as the probing source. The recording system consisted of a Spex 1870 monochromator, an 18 ELU-~ or FEU-84 photoelectric multiplier, and an $8-12 recording oscillograph. The measurements were carried out in a l-cm-long cuvette. We investigated EuAA, GdAA, TbAA, DyCI, HoCI, ErCI, TmCI, YbAA, LuAA complexes of etioporphyrin I (etio) in which an acetylacetonate group (AA) or chlorine atom was attached perpendicularly to the porphyrin ring with respect to the third valence of the rare-earth ion. Absolute ethanol was used as the solvent. The absorption spectra of all the investigated complexes were practically identical and consisted of two bands in the visible spectral region with maxima at 572 and 536 nm, corresponding to 0-0 and 0-i bands of the first electron transition (so-called Q (0, 0) and Q (0, i) bands) and an intense Soret band (B band) with %max = 403 nm belonging to the second electron transition. The luminescence characteristics of the investigated complexes are in agreement with the systematics of the photophysical properties of the complexes of porphyrins with rare-earth elements (see [4]). Reversible changes, whose nature depended on the rare-earth ion, were observed in the absorption spectra of etio rare-earth complexes under the effect of a 532-nm laser pulse. In the case of Gd- and Lu-etio, the clarification of the initial Q (0, 0), Q (0, i), and B bands was accompanied by the appearance of new absorption in the entire visible and near IR spectral regions. The differential spectrum of non-steady-state absorption for Gdetio is shown in Fig. la. The differential spectrum for Lu-etio has a similar appearance (Fig. ib). The duration of the clarification and induced-absorption processes coincided with each other and also with the phosphorescence lifetime measured experimentally in degassed solutions and was 20 and 30 Dsec for Gd- and Lu-etio, respectively. Injection of