Ultrafast Electron Transfer Dynamics in a Series of Porphyrin/Viologen Complexes

Involvement of Electronically Excited Radical Pair Products

Jonas Petersson, Leif Hammarström

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

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 S2 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.

Original languageEnglish
Pages (from-to)7531-7540
Number of pages10
JournalJournal of Physical Chemistry B
Volume119
Issue number24
DOIs
Publication statusPublished - Jun 18 2015

Fingerprint

Viologens
Porphyrins
porphyrins
electron transfer
Electrons
products
Ground state
molecular relaxation
ground state
Metalloporphyrins
Laser excitation
Excited states
excitation
Rate constants
aqueous solutions
life (durability)

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Materials Chemistry
  • Surfaces, Coatings and Films

Cite this

@article{c5300f1b0f0247cba4b8f527ce761bff,
title = "Ultrafast Electron Transfer Dynamics in a Series of Porphyrin/Viologen Complexes: Involvement of Electronically Excited Radical Pair Products",
abstract = "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 S2 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.",
author = "Jonas Petersson and Leif Hammarstr{\"o}m",
year = "2015",
month = "6",
day = "18",
doi = "10.1021/jp5113119",
language = "English",
volume = "119",
pages = "7531--7540",
journal = "Journal of Physical Chemistry B",
issn = "1520-6106",
publisher = "American Chemical Society",
number = "24",

}

TY - JOUR

T1 - Ultrafast Electron Transfer Dynamics in a Series of Porphyrin/Viologen Complexes

T2 - Involvement of Electronically Excited Radical Pair Products

AU - Petersson, Jonas

AU - Hammarström, Leif

PY - 2015/6/18

Y1 - 2015/6/18

N2 - 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 S2 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.

AB - 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 S2 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.

UR - http://www.scopus.com/inward/record.url?scp=84934908985&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84934908985&partnerID=8YFLogxK

U2 - 10.1021/jp5113119

DO - 10.1021/jp5113119

M3 - Article

VL - 119

SP - 7531

EP - 7540

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 24

ER -