OPTICALLY DETECTED MAGNETIC-RESONANCE IN THE LOWEST TRIPLET-STATE OF PD(2-THPY)(2)

An optically detected magnetic resonance (ODMR) study of the lowest ex cited state of Pd(2-thpy)(2) ((2-thpy)(-) = 2-thienylpyridinate) in an n-octane Shpol'skii matrix at T = 1.4 K is reported. The results in z ero and low magnetic fields allow us to characterize the emissive trip let state in more detail. In this state the spin-orbit contributions t o the zero-field splittings of the triplet substates are much more pro nounced than for analogous Rh(III) chelate complexes. Microwave recove ry experiments display the emission lifetimes of 134 mu s and 1200 mu s of two triplet substates, which are split by 2E = 2886 MHz (0.0962 c m(-1)). The D value characterizing the relative energy of the third su blevel is larger than 6600 MHz (0.22 cm(-1)) and is outside the microw ave range of our experimental equipment. However, its decay time can b e determined to be 235 mu s. Moreover, phosphorescence microwave doubl e-resonance (PMDR) experiments reveal a spin selectivity in the vibrat ional satellite lines of the emission spectrum. Such a phenomenon is o bserved for the first time for transition-metal compounds. The selecti vity is a consequence of different mechanisms of radiative vibronic de activations from the different emissive triplet sublevels.