Conservation of vibrational coherence in ultrafast electronic relaxation: The case of diplatinum complexes in solution

Abstract

We report the results of ultrafast transient absorption studies of tetrakis(μ-pyrophosphito)diplatinate(II), [Pt_2(μ-P_2O_5H_2)_4]^(4−) (Pt(pop)) and its perfluoroborated derivative [Pt_2(μ-P_2O_5(BF_2)_4]^(4−) (Pt(pop-BF_2)) in water and acetonitrile upon excitation of high lying (<300 nm) UV absorption bands. We observe an ultrafast relaxation channel from high lying states to the lowest triplet state that partly (Pt(pop) in H_2O, Pt(pop-BF_2)) or fully (Pt(pop) in MeCN) bypasses the lowest singlet excited state. As a consequence, vibrational wave packets are detected in the lowest triplet state and/or the lowest excited singlet of both complexes, even though the electronic relaxation cascade spans ca. 2 and 1.3 eV, respectively. In the case of Pt(pop-BF_2), coherent wave packets generated by optical excitation of the lowest singlet ^1A_(2u) state also are reported. Overall, the reported dephasing times of the Pt-Pt oscillator in the ground, singlet and triplet states do not depend much on the solvent or the molecular structure.

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