Ultrafast Electron Transfer Dynamics in a Series of Porphyrin/Viologen Complexes: Involvement of Electronically Excited Radical Pair Products
2015 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 119, no 24, 7531-7540 p.Article in journal (Refereed) Published
Ultrafast electron transfer was studied for a series of metalloporphyrin/bipyridinium complexes in aqueous solution, using laser excitation in the Soret or Q-bands of the porphyrin. Electron transfer occurred before electronic and vibrational relaxation of the initial excited state. This allowed for a thorough investigation of the dependence of electron transfer rate constants on the driving force and the nature of the product state. The driving force dependence showed that electron transfer from the S-2 state occurred to an electronically excited radical pair state, and the present results provide the most direct evidence to date for the formation of such states in photoinduced electron transfer reactions. We also found that subsequent recombination of the radical pair produced vibrationally excited ground states; the excess energy of the radical pair generated from the initial state is not completely dissipated during the lifetime of the radical pair. The porphyrin/bipyridinium complexes where recombination lies deeper in the Marcus inverted region show less formation of unrelaxed ground states, contrary to what is expected from equilibrium electron transfer theories. Instead, the rate of the electron transfer, which competes with vibrational relaxation, was the main parameter controlling the relative yield of unrelaxed ground states within this series of complexes.
Place, publisher, year, edition, pages
2015. Vol. 119, no 24, 7531-7540 p.
electron transfer, electronically excited states, unrelaxed ground states, hot ground states, porphyrin, S2, ZnTPPS, MgTPPS, viologen, vibrational relaxation
Research subject Chemistry with specialization in Chemical Physics
IdentifiersURN: urn:nbn:se:uu:diva-235459DOI: 10.1021/jp5113119ISI: 000356754800043PubMedID: 25766332OAI: oai:DiVA.org:uu-235459DiVA: diva2:760410