Two-Photon Spectra of Chlorophylls and Carotenoid-Tetrapyrrole Dyads

Daniel A. Gacek, Ana L Moore, Thomas A Moore, Peter Jomo Walla

Research output: Contribution to journalArticle

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Abstract

We present a direct comparison of two-photon spectra of various carotenoid-tetrapyrrole dyads and phthalocyanines (Pc) as well as chlorophylls (Chl) in the spectral range between 950 and 1360 nm, corresponding to one-photon spectra between 475 and 680 nm. For carotenoids (Car) with 8, 9, or 10 conjugated double bonds, the two-photon absorption cross section of states below the optical allowed carotenoid S2 is at least about 3-10 times higher than that of Pc or chlorophyll a and b at 550/1100 nm. A quantitative comparison of spectra from Pc with and without carotenoids of eight and nine conjugated double bonds confirms energy transfer from optically forbidden carotenoid states to Pc in these dyads. When considering that less than 100% efficient energy transfer reduces the two-photon contribution of the carotenoids in the spectra, the actual Car two-photon cross sections relative to Chl/Pc are even higher than a factor of 3-10. In addition, strong spectroscopic two-photon signatures at energies below the optical allowed carotenoid S2 state support the presence of additional optical forbidden carotenoid states such as S∗, Sx, or, alternatively, contributions from higher vibronic or hot S1 states dominating two-photon spectra or energy transfer from the carotenoids. The onset of these states is shifted about 1500-3500 cm-1 to lower energies in comparison to the S2 states. Our data provides evidence that two-photon excitation of the carotenoid S∗, Sx, or hot S1 states results in energy transfer to tetrapyrroles or chlorophylls similar to that observed with the Car S1 two-photon excitation.

Original languageEnglish
Pages (from-to)10055-10063
Number of pages9
JournalJournal of Physical Chemistry B
Volume121
Issue number43
DOIs
Publication statusPublished - Nov 2 2017

Fingerprint

Tetrapyrroles
carotenoids
chlorophylls
Chlorophyll
Carotenoids
Photons
photons
Energy transfer
energy transfer
absorption cross sections
excitation

ASJC Scopus subject areas

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

Cite this

Two-Photon Spectra of Chlorophylls and Carotenoid-Tetrapyrrole Dyads. / Gacek, Daniel A.; Moore, Ana L; Moore, Thomas A; Walla, Peter Jomo.

In: Journal of Physical Chemistry B, Vol. 121, No. 43, 02.11.2017, p. 10055-10063.

Research output: Contribution to journalArticle

Gacek, Daniel A. ; Moore, Ana L ; Moore, Thomas A ; Walla, Peter Jomo. / Two-Photon Spectra of Chlorophylls and Carotenoid-Tetrapyrrole Dyads. In: Journal of Physical Chemistry B. 2017 ; Vol. 121, No. 43. pp. 10055-10063.
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AB - We present a direct comparison of two-photon spectra of various carotenoid-tetrapyrrole dyads and phthalocyanines (Pc) as well as chlorophylls (Chl) in the spectral range between 950 and 1360 nm, corresponding to one-photon spectra between 475 and 680 nm. For carotenoids (Car) with 8, 9, or 10 conjugated double bonds, the two-photon absorption cross section of states below the optical allowed carotenoid S2 is at least about 3-10 times higher than that of Pc or chlorophyll a and b at 550/1100 nm. A quantitative comparison of spectra from Pc with and without carotenoids of eight and nine conjugated double bonds confirms energy transfer from optically forbidden carotenoid states to Pc in these dyads. When considering that less than 100% efficient energy transfer reduces the two-photon contribution of the carotenoids in the spectra, the actual Car two-photon cross sections relative to Chl/Pc are even higher than a factor of 3-10. In addition, strong spectroscopic two-photon signatures at energies below the optical allowed carotenoid S2 state support the presence of additional optical forbidden carotenoid states such as S∗, Sx, or, alternatively, contributions from higher vibronic or hot S1 states dominating two-photon spectra or energy transfer from the carotenoids. The onset of these states is shifted about 1500-3500 cm-1 to lower energies in comparison to the S2 states. Our data provides evidence that two-photon excitation of the carotenoid S∗, Sx, or hot S1 states results in energy transfer to tetrapyrroles or chlorophylls similar to that observed with the Car S1 two-photon excitation.

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