Third order nonlinear optical properties of stacked bacteriochlorophylls in bacterial photosynthetic light-harvesting proteins

L. X. Chen*, Philip D. Laible, Frank C. Spano, Eric S. Manas

*Corresponding author for this work

Research output: Contribution to journalConference articlepeer-review

4 Scopus citations


Enhancement of the nonresonant second order molecular hyperpolarizabilities γ were observed in stacked macrocyclic molecular systems, previously in a μ-oxo silicon phthalocyanine (SiPcO) monomer, dimer and trimer series, and now in bacteriochlorophyll a (BChla) arrays of light harvesting (LH) proteins. Compared to monomeric BChla in a tetrahydrofuran (THF) solution, the 〈γ〉 for each macrocycle was enhanced in naturally occurring stacked macrocyclic molecular systems in the bacterial photosynthetic LH proteins where BChla's are arranged in tilted face-to-face arrays. In addition, the γ enhancement is more significant in B875 of LH1 than in B850 in LH2. Theoretical modeling of the nonresonant γ enhancement using simplified molecular orbitals for model SiPcO indicated that the energy level of the two photon state is crucial to the γ enhancement when a two photon process is involved. Additionally, charge transfer between the monomers may be important if this produces states which are close to one-photon resonance. The calculated results can be extended to γ enhancement in B875 and B850 arrays, suggesting that BChla in B875 are more strongly coupled than in B850. In addition, a 50-160 fold increase in 〈γ〉 for the S1 excited state of relative to S0 of bacteriochlorophyll in vivo was observed which provides an alternative method for probing excited state dynamics and a potential application for molecular switching.

Original languageEnglish (US)
Pages (from-to)178-184
Number of pages7
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - 1997
EventNonlinear Optical Properties of Organic Materials X - San Diego, CA, United States
Duration: Jul 30 1997Aug 1 1997


  • Bacteriochlorophyll
  • Degenerate four wave mixing
  • Light harvesting protein
  • Phthalocyanine
  • Third order nonlinear optical response

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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