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Femtosecond dynamics of metal-centered and ligand-to-metal charge-transfer (t2g-based) electronic excited states in various solvents: A comprehensive study of IrBr6 2.
Matveev, Sergey M; Budkina, Darya S; Zheldakov, Igor L; Phelan, Michael R; Hicks, Christopher M; Tarnovsky, Alexander N.
Afiliación
  • Matveev SM; Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University,Bowling Green, Ohio 43403, USA.
  • Budkina DS; Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University,Bowling Green, Ohio 43403, USA.
  • Zheldakov IL; Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University,Bowling Green, Ohio 43403, USA.
  • Phelan MR; Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University,Bowling Green, Ohio 43403, USA.
  • Hicks CM; Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University,Bowling Green, Ohio 43403, USA.
  • Tarnovsky AN; Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University,Bowling Green, Ohio 43403, USA.
J Chem Phys ; 150(5): 054302, 2019 Feb 07.
Article en En | MEDLINE | ID: mdl-30736677
The photophysical properties of intraconfigurational metal-centered (MC) and ligand-to-metal charge transfer (LMCT) states were studied in a prototype low spin heavy d5 transition metal complex, IrBr6 2-. The femtosecond-to-picosecond dynamics of this complex was investigated in solutions of drastically different polarity (acetonitrile, chloroform, and water) by means of ultrafast broadband transient absorption spectroscopy. We observed that the system, when excited into the third excited [second LMCT, 2Uu'(T1u)] state, undergoes distortion from the Franck-Condon geometry along the t2g vibrational mode as a result of the Jahn-Teller effect, followed by rapid internal conversion to populate (90 fs) the second excited [first LMCT, 2Ug'(T1g)] state. Vibrational decoherence and vibrational relaxation (∼400 fs) in 2Ug'(T1g) precede the decay of this state via internal conversion (time constants, 2.8 and 3 ps in CH3CN and CHCl3 and 0.76 ps in water), which can also be viewed as back electron transfer and which leads into the intraconfigurational MC 2Ug'(T2g) state. This is the lowest-excited state, from which the system returns to the ground state. This MC state is metastable in both CH3CN and CHCl3 (lifetime, ∼360 ps), but is quenched via OH-mediated energy transfer in aqueous environments, with the lifetime shortening up to 21 ps in aqueous solutions. The cascade relaxation mechanism is the same upon excitation into the second excited state. Excitation of IrBr6 2- in chloroform into higher 2Uu'(T2u), 2Eu″(T2u), and 2Eg'(T1g) states is observed to populate the third excited 2Uu'(T1u) state within 100 fs. These experiments allow us to resolve the ultrafast relaxation coordinate and emphasize that the excited-state Jahn-Teller effect is a driving force in the ultrafast dynamics, even for heavy transition metal complexes with very significant spin-orbit interactions.

Texto completo: 1 Colección: 01-internacional Banco de datos: MEDLINE Idioma: En Revista: J Chem Phys Año: 2019 Tipo del documento: Article País de afiliación: Estados Unidos

Texto completo: 1 Colección: 01-internacional Banco de datos: MEDLINE Idioma: En Revista: J Chem Phys Año: 2019 Tipo del documento: Article País de afiliación: Estados Unidos