Target analysis is employed to resolve the ground and excited state properties from simultaneously measured Femtosecond Stimulated Raman Spectra (FSRS) and Transient Absorption Spectra (TAS). FSRS is a three-pulse technique, involving picosecond Raman pump pulses and femtosecond visible pump and probe pulses. The TAS are needed to precisely estimate the properties of the Instrument Response Function. The prezero "coherent artifact" present during the overlap of the three pulses is described by a damped oscillation with a frequency (ω - ωn) where ωn is a ground state resonance Raman frequency. Simultaneous target analysis of the FSRS and TAS allows the complete excited state dynamics to be resolved with a time resolution better than 100 fs. The model system studied is the carotenoid lycopene in tetrahydrofuran. The lycopene dynamics show a spectral evolution with seven states, including a biphasic cooling process during the S2-S1 internal conversion, multiple S1 lifetimes, and an S* state decaying with a lifetime of 7 ps.

• Publikační typ
• časopisecké články MeSH

Carotenoids are an integral part of natural photosynthetic complexes, with tasks ranging from light harvesting to photoprotection. Their underlying energy deactivation network of optically dark and bright excited states is extremely efficient: after excitation of light with up to 2.5 eV of photon energy, the system relaxes back to ground state on a time scale of a few picoseconds. In this article, we summarize how a model based on the vibrational energy relaxation approach (VERA) explains the main characteristics of relaxation dynamics after one-photon excitation with special emphasis on the so-called S* state. Lineshapes after two-photon excitation are beyond the current model of VERA. We outline this future line of research in our article. In terms of experimental method development, we discuss which techniques are needed to better describe energy dissipation effects in carotenoids and within the first solvation shell.

• MeSH
• fotony MeSH
• fotosyntetická reakční centra (proteinové komplexy) * MeSH
• karotenoidy * MeSH
• světlosběrné proteinové komplexy MeSH
• vibrace MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• fotosyntetická reakční centra (proteinové komplexy) * MeSH
• karotenoidy * MeSH
• světlosběrné proteinové komplexy MeSH

In some molecular systems, such as nucleobases, polyenes or the active ingredients of sunscreens, substantial amounts of photo-excitation energy are dissipated on a sub-picosecond time scale, raising questions such as: where does this energy go or among which degrees of freedom it is being distributed at such early times? Here we use transient absorption spectroscopy to track excitation energy dispersing from the optically accessible vibronic subsystem into the remaining vibrational subsystem of the solute and solvent. Monitoring the flow of energy during vibrational redistribution enables quantification of local molecular heating. Subsequent heat dissipation away from the solute molecule is characterized by classical thermodynamics and molecular dynamics simulations. Hence, we present a holistic approach that tracks the internal temperature and vibronic distribution from the act of photo-excitation to the restoration of the global equilibrium. Within this framework internal vibrational redistribution and vibrational cooling are emergent phenomena. We demonstrate the validity of the framework by examining a highly controversial example, carotenoids. We show that correctly accounting for the local temperature unambiguously explains their energetically and temporally congested spectral dynamics without the ad hoc postulation of additional 'dark' states. An immediate further application of this approach would be to monitor the excitation and thermal dynamics of pigment-protein systems.

• Publikační typ
• časopisecké články MeSH

RC-LH1-PufX complexes from a genetically modified strain of Rhodobacter sphaeroides that accumulates carotenoids with very long conjugation were studied by ultrafast transient absorption spectroscopy. The complexes predominantly bind the carotenoid diketospirilloxanthin, constituting about 75% of the total carotenoids, which has 13 conjugated C=C bonds, and the conjugation is further extended to two terminal keto groups. Excitation of diketospirilloxanthin in the RC-LH1-PufX complex demonstrates fully functional energy transfer from diketospirilloxanthin to BChl a in the LH1 antenna. As for other purple bacterial LH complexes having carotenoids with long conjugation, the main energy transfer route is via the S2-Qx pathway. However, in contrast to LH2 complexes binding diketospirilloxanthin, in RC-LH1-PufX we observe an additional, minor energy transfer pathway associated with the S1 state of diketospirilloxanthin. By comparing the spectral properties of the S1 state of diketospirilloxanthin in solution, in LH2, and in RC-LH1-PufX, we propose that the carotenoid-binding site in RC-LH1-PufX activates the ICT state of diketospirilloxanthin, resulting in the opening of a minor S1/ICT-mediated energy transfer channel.

• Klíčová slova
• Carotenoids, Energy transfer, Intramolecular charge transfer state, Light-harvesting, Purple bacteria, Ultrafast spectroscopy,
• MeSH
• bakteriochlorofyly metabolismus   MeSH
• fluorescenční spektrometrie MeSH
• karotenoidy metabolismus   MeSH
• kinetika MeSH
• počítačové zpracování signálu MeSH
• přenos energie * MeSH
• Rhodobacter sphaeroides metabolismus   MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• vysokoúčinná kapalinová chromatografie MeSH
• xanthofyly metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bakteriochlorofyly MeSH
• karotenoidy MeSH
• spirilloxanthin MeSH Prohlížeč
• světlosběrné proteinové komplexy MeSH
• xanthofyly MeSH

In π-conjugated chain molecules such as carotenoids, coupling between electronic and vibrational degrees of freedom is of central importance. It governs both dynamic and static properties, such as the time scales of excited state relaxation as well as absorption spectra. In this work, we treat vibronic dynamics in carotenoids on four electronic states (|S0⟩, |S1⟩, |S2⟩, and |Sn⟩) in a physically rigorous framework. This model explains all features previously associated with the intensely debated S* state. Besides successfully fitting transient absorption data of a zeaxanthin homologue, this model also accounts for previous results from global target analysis and chain length-dependent studies. Additionally, we are able to incorporate findings from pump-deplete-probe experiments, which were incompatible to any pre-existing model. Thus, we present the first comprehensive and unified interpretation of S*-related features, explaining them by vibronic transitions on either S1, S0, or both, depending on the chain length of the investigated carotenoid.

• Publikační typ
• časopisecké články MeSH