Optically detected magnetic resonance in the lowest triplet state of Pd(2-thpy)₂

Abstract

An optically detected magnetic resonance (ODMR) study of the lowest excited 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 zero and low magnetic fields allow us to characterize the emissive triplet state in more detail. In this state the spin-orbit contributions to the zero-field splittings of the triplet substates are much more pronounced than for analogous Rh(III) chelate complexes. Microwave recovery experiments display the emission lifetimes of 134 μs and 1200 μs of two triplet substates, which are split by 2E = 2886 MHz (0.0962 cm⁻¹). The D value characterizing the relative energy of the third sublevel is larger than 6600 MHz (0.22 cm⁻¹) and is outside the microwave range of our experimental equipment. However, its decay time can be determined to be 235 μs. Moreover, phosphorescence microwave double-resonance (PMDR) experiments reveal a spin selectivity in the vibrational satellite lines of the emission spectrum. Such a phenomenon is observed for the first time for transition-metal compounds. The selectivity is a consequence of different mechanisms of radiative vibronic deactivations from the different emissive triplet sublevels.