Vibrational satellite structure

The vibrational satellite structures in the highly resolved emission of Pt(4,6-dFppy) (acac) in n-octane display the different properties of the triplet substates in a very characteristic manner. Figure 6 shows the selectively excited emission spectra in -octane at temperatures of 1.2, 4.2, and 20 K, together with a spectrum obtained at 77 K for comparison. 

Further temperature increase from 4.2 to 20 K does not lead to significant changes of the emission. Interestingly, the most intense HT induced satellites of substate I (e.g., 344,441 cm-1) can still be detected at 20 K. Vibronic coupling with respect to substate I seems to be very strong for these specific HT active modes. Although the vibrational satellite structure at 20 K is dominated by the emission stemming from the substates II/III, several weak satellites from substate I are also observed. 

Time-resolved emission spectra (Sect. 3.1.4, Fig. 8) show that the triplet sublevels I and III exhibit very different emission spectra with respect to their vibrational satellite structures. The long-lived state I is mainly vibronically (Herz-berg-Teller, HT) deactivated, while the emission from state III is dominated by vibrational satellites due to Franck-Condon (FC) activities, whereby both types of vibrational modes exhibit different frequencies. This behavior makes it attractive to measure a PMDR spectrum. 

The vibrational satellite structures that occur in the emission and excitation spectra (e.g.see Figs. 13 to 15) result from different vibrational activities, namely from vibronic or Herzberg-Teller activity, as introduced in this section, and from Franck-Condon activity, as discussed in the next section. 

The emission spectrum of Pt(2-thpy)2 recorded at T = 1.3 K exhibits a rich and highly informative vibrational satellite structure (Fig. 13). This structure seems... 

The vibrational satellite structure, for example of the emission spectrum, is altered due to two different effects. First, because of the red shift of the vibrational modes, as mentioned above, one observes the satelHtes at lower energies relative to the electronic origin. Secondly, the vibronic coupling property of a vibrational mode depends on the specific normal coordinate of that individual mode. Since the coordinates partly change with deuteration, the intensity of the corresponding vibronic satellite maybe modified distinctly. (Compare the Refs. [168, 169,173,175].) This effect is also observed, when the vibronic intensities found for Pt(2-thpy-hg)2 are compared to those of Pt(2-thpy-dg)2, as is shown below in Fig. 25 and in Ref. [23]. 

The vibrational satellite structure corresponding to the emission of the electronic state I is distinctly altered due to the perdeuteration. As expected (Sect. 4.2.10.1), all vibrational frequencies are red shifted, apart from the phonon satellite of 15 cm h However, by using the intensity distributions of the vibrational satellites, it is possible to correlate many of the vibrational modes of the perprotonated to those of the perdeuterated compound, as is carried out in Fig. 25. 

Pd(2-thpy)2 was investigated by applying the methods of time-resolved emission (Fig. 8) and phosphorescence-microwave double resonance (PMDR) spectroscopy (Fig. 10). By both methods, the vibrational satellite structures are resolved and reveal spin selectivity in these satellites. Thus, vibrational satellites can be assigned to the respective triplet substates. The complementary character of these two methods is demonstrated for the first time for transition metal compounds [58,61] (Compare Sects. 3.1.4 and 3.1.5.). 

Interestingly, the time-resolved and highly resolved emission spectra [83] show that, in particular, these triplet sublevels exhibit very different emission spectra with respect to their vibrational satellite structures. The long living state... 

Figure 3 illustrates low-temperature emission and excitation spectra of [Pt(bpy-Ii8)2] in two different matrices [44, 68, 75]. These spectra are by a factor of about 300 better resolved than published to date (cf. [52, 58] Fig. 2). The well-resolved electronic origins and the vibrational satellite structures reveal an enormous amount of information, which will be analyzed in the following sections.

However, even the longest decay component of r, = 50 ps is relatively short compared to the decay times measured for the uncoordinated bpy (4 s, 0.77 s, and 0.38 s at T = 1.2 K [82]). From this behavior and the fact that the triplet can be directly exited, it is concluded that the triplet sublevels contain at least some admixture of higher lying singlet states, due to spin-orbit coupling induced by platinum. Further support for this result comes from an analysis of the vibrational satellite structures, in particular, from the weak occurrence of vibrational metal-ligand (M-L) sattelites in the emission spectra (Sect 2.3). 

Further, all clearly discernible peaks in the emission spectra at energies greater than about 1650 cm are assigned to combinations of prominent vibrational modes or to higher members of very weak Franck-Condon progressions (Table 2). The occurrence of combinations with weak intensities in the vibrational satellite structures indicates small shifts along different normal coordinates (e.g., see [100]). 

Beside the shift of the electronic transition energy, the emission properties of [Pt(bpy-d8)2] exhibit fiorther changes with respect to [Pt(bpy-h8)2]. Similar effects are well known and are usually observed upon deuteration of emitting centers (e.g., see [37, 44, 60, 74, 85,102-107]). In particular, (1) all vibrational energies are red-shifted. A correlation of several vibrational modes of both compounds is carried out in Fig. 6 and Table 2 using in part the information worked out for [Rhfbpylj], for example, to correlate the 719 cm" /767 cm" modes (cf. [60]). (2) The intensity distribution of the vibrational satellite structure is changed to some extent due to alterations of the forms (PEDs) of the normal coordinates (cf. [106]). 

---