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Ultrafast Dynamics of meso ‐Tetraphenylmetalloporphyrins: The Role of Dark States

Ultrafast Dynamics of meso ‐Tetraphenylmetalloporphyrins: The Role of Dark States Studying the relaxation pathways of porphyrins and related structures upon light absorption is crucial to understand the fundamental processes of light harvesting in biosystems and many applications. Herein, we show by means of transient absorption studies, following Q‐ and Soret‐band excitation, and ab initio calculations on meso‐tetraphenylporphyrinato magnesium(II) (MgTPP) and meso‐tetraphenylporphyrinato cadmium(II) (CdTPP) that electronic relaxation following Soret‐band excitation of porphyrins with a heavy central atom is mediated by a hitherto disregarded dark state. This accounts for an increased rate of internal conversion. The dark state originates from an orbital localized at the central nitrogen atoms and its energy continuously decreases along the series from magnesium to zinc to cadmium to below 2.75 eV for CdTPP dissolved in tetrahydrofuran. Furthermore, we are able to directly trace fast intersystem crossing in the cadmium derivative, which takes place within (110±20) ps. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png ChemPlusChem Wiley

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References (60)

Publisher
Wiley
Copyright
Copyright © 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim
ISSN
2192-6506
eISSN
2192-6506
DOI
10.1002/cplu.201300143
Publisher site
See Article on Publisher Site

Abstract

Studying the relaxation pathways of porphyrins and related structures upon light absorption is crucial to understand the fundamental processes of light harvesting in biosystems and many applications. Herein, we show by means of transient absorption studies, following Q‐ and Soret‐band excitation, and ab initio calculations on meso‐tetraphenylporphyrinato magnesium(II) (MgTPP) and meso‐tetraphenylporphyrinato cadmium(II) (CdTPP) that electronic relaxation following Soret‐band excitation of porphyrins with a heavy central atom is mediated by a hitherto disregarded dark state. This accounts for an increased rate of internal conversion. The dark state originates from an orbital localized at the central nitrogen atoms and its energy continuously decreases along the series from magnesium to zinc to cadmium to below 2.75 eV for CdTPP dissolved in tetrahydrofuran. Furthermore, we are able to directly trace fast intersystem crossing in the cadmium derivative, which takes place within (110±20) ps.

Journal

ChemPlusChemWiley

Published: Oct 1, 2013

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