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Deconstructing the excited-state dynamics of β-carotene in solution
Askat E Jailaubekov1, Mikas Vengris, Sang-Hun Song
1Department of Chemistry, University of California Davis, One Shields Avenue, Davis, California 95616, United States.
The Journal of Physical Chemistry. A
|February 5, 2011
Summary
Ultrafast dynamics of all-trans β-carotene reveal distinct pathways for excited-state generation. Temperature and excitation wavelength influence the S* quantum yield and decay, impacting carotenoid photophysics.
Area of Science:
- Photochemistry
- Biophysics
- Spectroscopy
Background:
- Carotenoids like all-trans β-carotene play crucial roles in light harvesting and photoprotection.
- Understanding their excited-state dynamics is essential for elucidating these functions.
- Previous studies have indicated complex relaxation pathways, but the role of specific states and environmental factors remains debated.
Purpose of the Study:
- To characterize the femtosecond to nanosecond dynamics of all-trans β-carotene in 3-methylpentane.
- To investigate the influence of excitation wavelength and temperature on excited-state populations.
- To develop a refined model for carotenoid excited-state relaxation.
Main Methods:
- Ultrafast dispersed transient absorption spectroscopy was employed.
- Experiments were conducted at varying excitation wavelengths (400 nm and 490 nm) and temperatures (298 K and 77 K).
- A modified multicompartment model was developed to analyze the kinetic data.
Main Results:
- The S* population kinetics were resolved across all experimental conditions.
- A temperature-dependent and excitation wavelength-dependent S* quantum yield was observed, attributed to competing pathways.
- The S* decay time scale significantly increased at lower temperatures, indicating structural relaxation.
- The triplet state was observed for the first time under low-energy excitation, originating from S(2), not S* or S(1).
- No population flow between S* and S(1) was detected.
Conclusions:
- The study provides a detailed understanding of all-trans β-carotene excited-state dynamics.
- A competition between pathways leading to S(1) and S* generation is confirmed, influenced by energy barriers.
- Structural relaxation significantly affects the S* decay.
- The origin of the triplet state was clarified, ruling out S* and S(1) as precursors under specific conditions.
- Sample purity was confirmed not to be the primary cause of the S* state.
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