TIME-RESOLVED VIBRATIONAL-STRUCTURES OF THE TRIPLET SUBLEVEL EMISSIONOF PD(2-THPY)(2)

Time-resolved phosphorescence spectra from the lowest electronic tripl et of Pd(2-thpy)(2) (with 2-thpy(-) = ortho-C-deprotonated form of 2-( 2-thienyl)pyridine) (see the inset of Figure 2) are presented. The com plex was isolated in a Shpol'skii matrix to obtain high resolution. Th e emitting triplet lies at 18 418 +/- 1 cm(-1) (electronic origin). It s zero-field splitting is less than 1 cm(-1) and could not be resolved optically. However, at 1.3 K, when the spin-lattice relaxation is slo w compared to the emission lifetimes of the sublevels (130, 235, 1200 mu s), the individual sublevels emit independently. Thus, by time-reso lved spectroscopy it is possible to separate a fast-decaying emission spectrum from a slow-decaying one. A highlight of this investigation i s that these spectra exhibit different vibrational satellite structure s. This shows that different spin-orbit coupling mechanisms (direct sp in-orbit coupling and Herzberg-Teller coupling) govern the radiative d eactivation of the sublevels. In particular, it is found that specific vibrational modes couple very selectively to individual sublevels. Fo r example, the 528 cm(-1) mode couples only to the slow-decaying suble vel. Thus, these optically well resolvable vibrational satellites disp lay directly properties of the individual sublevels, which are unresol vable by conventional optical spectroscopy. This effect is observed fo r the first time for transition metal complexes.