Zeeman and optical experiments on the lowest triplet state of palladium porphin

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Abstract
Zeeman and variable temperature experiments on the lowest (optically excited) triplet state of palladium porphin (PdP) in single crystals of n-octane (n-C 8) and n-decane (n-C10) performed at low temperatures are reported. The orbital degeneracy of the 3 Eu state of the free molecule appears to be lifted in the crystal and the splitting between the two orbital components |x> and |y> amounts to 57 cm-1 for n-C8 and 41 cm-1 for n-C10. The triplet state parameters for PdP in n-C8 are D = - 23 ± 5 GHz, g ⊥ = 2·00 ± 0·02, g ‖ = 1·68 ± 0·04, and for PdP in n-C10 they are D = -42 ± 5 GHz, g ⊥ = 2·00 ± 0·01, g ‖ = 1·51 ± 0·03. The zero field splitting and g-tensor anisotropy are dominated by contributions from the spin-orbit coupling which connects the τ x , τ y levels of the 3|x> with those of the 3|y> state by a matrix element which has a magnitude of Z′ = 14·6 ± 0·3 cm-1. The orbital angular momentum in units of ħ in the 3 Eu state amounts to Λ′ = 1·4 ± 0·1. In accordance with theory Z′ and Λ′ appear to be independent of the host. The directions of the canonical axes in the lowest triplet state of PdP in the A-site of n-octane have been determined with respect to the crystallographic axis system.