Dark Excited States of Carotenoid Regulated by Bacteriochlorophyll in Photosynthetic Light Harvesting
| Autor: | Masayuki Yoshizawa, Katsunori Nakagawa, Hideki Hashimoto, Mamoru Nango, Ryosuke Nakamura |
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| Rok vydání: | 2011 |
| Předmět: |
Population
Xanthophylls Rhodospirillum rubrum Photochemistry Absorption chemistry.chemical_compound Ultrafast laser spectroscopy Materials Chemistry Singlet state Photosynthesis Physical and Theoretical Chemistry Spectroscopy education Bacteriochlorophylls education.field_of_study biology Chemistry Spectrum Analysis Darkness biology.organism_classification Carotenoids Surfaces Coatings and Films Kinetics Dark state Excited state Bacteriochlorophyll |
| Zdroj: | The Journal of Physical Chemistry B. 115:3233-3239 |
| ISSN: | 1520-5207 1520-6106 |
| Popis: | In photosynthesis, carotenoids play important roles in light harvesting (LH) and photoprotective functions, which have been described mainly in terms of two singlet excited states of carotenoids: S(1) and S(2). In addition to the "dark" S(1) state, another dark state, S*, was recently identified and its involvement in photosynthetic functions was determined. However, there is no consistent picture concerning its nature or the mechanism of its formation. One particularly anomalous behavior obtained from femtosecond transient absorption (TA) spectroscopy is that the S*/S(1) population ratio depends on the excitation intensity. Here, we focus on the effect of nearby bacteriochlorophyll (BChl) on the relaxation dynamics of carotenoid in the LH complex. We performed femtosecond TA spectroscopy combined with pre-excitation of BChl in the reconstituted LH1 complex from Rhodospirillum rubrum S1. We observed that the energy flow from S(1), including its vibrationally excited hot states, to S* occurs only when nearby BChl is excited into Q(y), resulting in an increase in S*/S(1). We also examined the excitation-intensity dependence of S*/S(1) by conventional TA spectroscopy. A comparison between the pre-excitation effect and excitation-intensity dependence shows a strong correlation of S*/S(1) with the number of BChls excited into Q(y). In addition, we observed an increase in triplet formation as the S* population increased, indicating that S* is an electronic excited state that is the precursor to triplet formation. Our findings provide an explanation for observed spectroscopic features, including the excitation-intensity dependences debated so far, and offer new insights into energy deactivation mechanisms inherent in the LH antenna. |
| Databáze: | OpenAIRE |
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