Zusammenfassung
The first spectroscopic investigation of Pd(qol)₂ (qol⁻ = 8-quinolinolato-N, O = oxinate) dissolved in an n-octane matrix (Shpol'skii matrix) is reported. Application of several spectroscopic methods at liquid helium temperatures (typically, T = 1.2 K), such a site-selective and highly resolved luminescence and excitation spectroscopy, time-resolved emission spectroscopy, optically detected ...
Zusammenfassung
The first spectroscopic investigation of Pd(qol)₂ (qol⁻ = 8-quinolinolato-N, O = oxinate) dissolved in an n-octane matrix (Shpol'skii matrix) is reported. Application of several spectroscopic methods at liquid helium temperatures (typically, T = 1.2 K), such a site-selective and highly resolved luminescence and excitation spectroscopy, time-resolved emission spectroscopy, optically detected magnetic resonance, microwave recovery, phosphorescence microwave double-resonance, and magnetic fields, allows us to characterize the lowest excited electronic states in detail. In accord with previous assignments for the related Pt(qol)₂ it is shown that these lowest states represent intraligand charge-transfer states, namely, ¹ILCT and ³ILCT. The electronic origin of the ¹ILCT state lies at 20617 cm⁻¹ (site A). It exhibits a newly homogenous line width with a half-width of about 80 cm⁻¹ (fwhm), which corresponds to a lifetime of τ(¹ILCT) ca. 2 x 10⁻¹³ s. This value is even shorter than that found for Pt(qol)₂, presumably due to intersystem crossings and relaxations to dd* states. The electronic origin of the ³ILCT state lies at 16090 cm⁻¹ (site A), and its zero-field splittings (zfs) into three sublevels are 2E = 2356 MHz (0.0785 cm⁻¹) and D - E = 5241 MHz (0.175 cm⁻¹). The emission decay times of these three sublevels are determined at τ(I) = 90 ± 30 ms, τ(II) = 180 ± 10 μs, and τ(III) = 80 ± 10 μs. (Slightly different values are found for a second site B at 16167 cm⁻¹.) From the small values of zfs and the long emission decay times it is concluded that metal-d or MLCT admixtures to ³ILCT are very small. This result clearly reflects the ligand-centered character of the transition. The assignment as an ILCT transition is supported by the occurence of relatively strong vibrational satellites of Pd-N and Pd-O character in highly resolved emission spectra. Although the transition is ascribed to a charge-transfer process, the geometry changes between the ground state and ³ILCT are very small. The results found for Pd(qol)₂ are compared to those of companion studies of Pt(qol)₂ and Pt(qtl)₂ (qtl⁻ = 8-quinolinethiolato-N,S).