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

We report the results of ultrafast transient absorption studies of tetrakis(l-pyrophosphito) diplatinate(II), [Pt-2(mu-P(2)O(5)H2)(4)](4) (Pt(pop)) and its perfluoroborated derivative [Pt-2(mu-P2O5(BF2)(4)](4) (Pt(pop-BF2)) 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 H2O, Pt(pop-BF2)) 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-BF2), coherent wave packets generated by optical excitation of the lowest singlet 1A2u 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. (C) 2017 Elsevier B. V. All rights reserved.