Femtosecond dynamics of the photoexcited methyl viologen radical cation

Tilmann Häupl, Reiner Lomoth, Leif Hammarström

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Methyl viologen (N,N′-dimethyl-4,4′-bipyridine, abbreviated MV2+) is widely used in light-driven molecular devices, where it switches between the redox forms MV2+ and MV•+. Yet, little is known about the excited-state dynamics of the radical cationic form MV•+. Femtosecond pump-probe spectroscopy was used to investigate the excited state dynamics of the electrochemically generated MV̇+ in acetonitrile solution. Subpicosecond excitation of the D0-D1 transition at 730 nm led to rapid relaxation (700 fs), generating two intermediates in the transient absorption spectra. The longer-lived intermediate, with a lifetime of 16 ps, could be assigned to a vibrationally excited ground state of MV•+. Its absorption spectrum was very similar to the ground-state spectrum of MV•+ in both shape and extinction coefficients, but red-shifted by ca. 810 cm-1. This energy shift equal one quantum of the intraring C-C stretch mode. The shorter lived transient decayed with a time constant of 1.0 ± 0.1 ps and is possibly also a vibrationally excited ground state. Thus, our results show that the excited D1-state of MV•+ in acetonitrile solution relaxes on the subpicosecond time scale via at least one long-lived (τ = 16 ps) vibrationally excited ground state.

Original languageEnglish
Pages (from-to)435-438
Number of pages4
JournalJournal of Physical Chemistry A
Volume107
Issue number4
DOIs
Publication statusPublished - Jan 30 2003

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Paraquat
Ground state
Cations
Excited states
cations
ground state
excitation
acetonitrile
Absorption spectra
absorption spectra
time constant
extinction
switches
Switches
Pumps
Spectroscopy
pumps
life (durability)
probes
shift

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Femtosecond dynamics of the photoexcited methyl viologen radical cation. / Häupl, Tilmann; Lomoth, Reiner; Hammarström, Leif.

In: Journal of Physical Chemistry A, Vol. 107, No. 4, 30.01.2003, p. 435-438.

Research output: Contribution to journalArticle

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