Double-resonance spectroscopy of the jet-cooled free base and Cu(ii) complex of protoporphyrin IX

Joseph M. Beames, Andrew J. Hudson, Timothy D. Vaden, John P. Simons

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5 Scopus citations


The excited-state dynamics of porphyrins, and related compounds, impact on their applications as photosensitizers for tumor-targeting drugs and solar cells. Many researchers have examined the influence of non-planar distortions in the ground-state geometry on the properties of photoexcited states. We have identified the added importance of conformational changes in the excited state, relative to the initial geometry, on the resulting decay pathways. The ground-state structure and photodynamics of free-base and Cu(ii) complexes of protoporphyrin IX, laser desorbed into a cold supersonic expansion, have been investigated using infrared ion-dip spectroscopy combined with density-functional theory calculations. The vibrational bands associated with the N-H stretching mode of the free base are broader in the first electronically excited state, accessed via the Q band of protoporphyrin IX, than the corresponding bands in the ground-electronic state. This is attributed to rapid intersystem crossing in the excited state promoted by extension of the N-H bonds. Our calculations show that the stretching modes are highly anharmonic, which suggests the likelihood that other conformational changes are also taking place in the excited state.

Original languageEnglish (US)
Pages (from-to)14076-14081
Number of pages6
JournalPhysical Chemistry Chemical Physics
Issue number42
StatePublished - Nov 14 2010

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy
  • Physical and Theoretical Chemistry


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