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Proceedings Paper

Third-order nonlinear optical properties of stacked bacteriochlorophylls in bacterial photosynthetic light-harvesting proteins
Author(s): Lin X.Q. Chen; Philip D. Laible; Frank C. Spano; Eric S. Manas
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Paper Abstract

Enhancement of the nonresonant second order molecular hyperpolarizabilities y were observed in stacked macrocyclic molecular systems, previously in a t-oxo silicon phthalocyanme (SiPcO) monomer, dimer and trimer series, and now in bacteriochiorophyll a (BChla) arrays oflight harvesting (LH) proteins. Compared to monomeric BChla in a tetrahydrofuran (TifF) 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 ofrelative to S0 ofbacteriochlorophyll in vivo was observed which provides an alternative method for probing excited state dynamics and a potential application for molecular switching.

Paper Details

Date Published: 13 October 1997
PDF: 7 pages
Proc. SPIE 3147, Nonlinear Optical Properties of Organic Materials X, (13 October 1997); doi: 10.1117/12.284247
Show Author Affiliations
Lin X.Q. Chen, Argonne National Lab. (United States)
Philip D. Laible, Argonne National Lab. (United States)
Frank C. Spano, Temple Univ. (United States)
Eric S. Manas, Temple Univ. (United States)

Published in SPIE Proceedings Vol. 3147:
Nonlinear Optical Properties of Organic Materials X
Mark G. Kuzyk, Editor(s)

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