| 1. |
- Andersson, Johan, et al.
(författare)
-
New paradigm of transition metal polypyridine complex photochemistry
- 2004
-
Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1364-5498. ; 127, s. 295-305
-
Tidskriftsartikel (refereegranskat)abstract
- Using polarization sensitive ultrafast transient absorption spectroscopy we have studied energy transfer and excited state relaxation pathways in a tetranuclear transition metal [( osmium)( ruthenium)(3)] polypyridine complex. Contrary to the generally accepted picture of transition metal complex photochemistry we find that ultrafast energy transfer ( less than or equal to 60 fs) occurs from the excited singlet MLCT state of the peripheral Ru-chromophores to the central Os-core, in efficient competition with intersystem crossing. Energy transfer between relaxed triplet MLCT states is more than an order of magnitude slower ( 600 fs).
|
|
| 2. |
- Andersson, Johan, et al.
(författare)
-
Ultrafast singlet energy transfer competes with intersystem crossing in a multi-center transition metal polypyridine complex
- 2004
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 386:4-6, s. 336-341
-
Tidskriftsartikel (refereegranskat)abstract
- Transition metal polypyridine complexes are finding widespread applications within many areas of chemistry. For their light-induced processes, the generally accepted picture is that all function emanates from triplet states because the singlet states initially prepared by light absorption are depopulated via intersystem crossing on the 100-fs time scale, before they are significantly involved in chemical reactions. Here we show that this is not always true. With ultrafast spectroscopy applied to a (ruthenium)(3)-osmium complex we show that transition metal polypyridine complexes can be designed where energy transfer between excited singlet states located on different metal centers efficiently competes with intersystem crossing, thus decreasing population of the lower-lying triplet states and concomitant energy loss. (C) 2004 Elsevier B.V. All rights reserved.
|
|
| 3. |
- Billsten, Helena, et al.
(författare)
-
Dynamics of energy transfer from lycopene to bacteriochlorophyll in genetically-modified LH2 complexes of Rhodobacter sphaeroides
- 2002
-
Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 41:12, s. 4127-4136
-
Tidskriftsartikel (refereegranskat)abstract
- LH2 complexes from Rb. sphaeroides were modified genetically so that lycopene, with I I saturated double bonds, replaced the native carotenoids which contain 10 saturated double bonds. Tuning the S, level of the carotenoid in LH2 in this way affected the dynamics of energy transfer within LH2, which were investigated using both steady-state and time-resolved techniques. The S I energy of lycopene in n-hexane was determined to be similar to12 500 +/- 150 cm(-1), by direct measurement of the S-1-S-2 transient absorption spectrum using a femtosecond IR-probing technique, thus placing an upper limit on the S, energy of lycopene in the LH2 complex. Fluorescence emission and excitation spectra demonstrated that energy can be transferred from lycopene to the bacteriochlorophyll molecules within this LH2 complex. The energy-transfer dynamics within the mutant complex were compared to wild-type LH2 from Rb. sphaeroides containing the carotenoid spheroidene and from Rs. molischian1l7n, in which lycopene is the native carotenoid. The results show that the overall efficiency for Crt --> B850 energy transfer is similar to80% in lyco-LH2 and similar to95% in WT-LH2 of Rb. sphaeroides. The difference in overall Crt --> BChl transfer efficiency of lyco-LH2 and WT-LH2 mainly relates to the low efficiency of the Crt S-1 --> BChl pathway for complexes containing lycopene, which was 20% in lyco-LH2. These results show that in an LH2 complex where the Crt Si energy is sufficiently high to provide efficient spectral overlap with both B800 and B850 Q(y) states, energy transfer via the Crt S, state occurs to both pigments. However, the introduction of lycopene into the Rb. sphaeroides LH2 complex lowers the S-1 level of the carotenoid sufficiently to prevent efficient transfer of energy to the B 800 Q, state, leaving only the Crt S-1 --> B 850 channel, strongly suggesting that Crt S-1 --> BChl energy transfer is controlled by the relative Crt S-1 and BChl Q(y) energies.
|
|
| 4. |
- Billsten, Helena, et al.
(författare)
-
Dynamics of vibrational relaxation in the S-1 state of carotenoids having 11 conjugated C=C bonds
- 2002
-
Ingår i: Chemical Physics Letters. - 0009-2614. ; 355:5-6, s. 465-470
-
Tidskriftsartikel (refereegranskat)abstract
- Transient absorption spectra and kinetics in the 470-650 nm region were recorded for lycopene, P-carotene and zeaxanthin, all carotenoids with 11 conjugated double bonds, in two solvents with different polarity. Analysis of the red wing of the carotenoid SI-S, transition revealed presence of a pronounced shoulder at early delay times. The kinetics recorded at this low-energy shoulder of the SI-S, transition yields an additional decay component of 500-800 fs in addition to the main S, decay. This dynamics is ascribed to a vibrational relaxation in the S, state of the carotenoids. (C) 2002 Elsevier Science B.V. All rights reserved.
|
|
| 5. |
- Billsten, Helena, et al.
(författare)
-
Excited-state processes in the carotenoid zeaxanthin after excess energy excitation
- 2005
-
Ingår i: The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory. - : American Chemical Society (ACS). - 1520-5215. ; 109:31, s. 6852-6859
-
Tidskriftsartikel (refereegranskat)abstract
- Aiming for better understanding of the large complexity of excited-state processes in carotenoids, we have studied the excitation wavelength dependence of the relaxation dynamics in the carotenoid zeaxanthin. Excitation into the lowest vibrational band of the S-2 state at 485 nm, into the 0-3 vibrational band of the S2 state at 400 nm, and into the B-2(u)+ state at 266 nm resulted in different relaxation patterns. While excitation at 485 nm produces the known four-state scheme (S-2 -> hot S-1 -> S-1 -> S-0), excess energy excitation led to additional dynamics occurring with a time constant of 2.8 ps (400 nm excitation) and 4.9 ps (266 nm excitation), respectively. This process is ascribed to a conformational relaxation of conformers generated by the excess energy excitation. The zeaxanthin S* state was observed regardless of the excitation wavelength, but its population increased after 400 and 266 nm excitation, suggesting that conformers generated by the excess energy excitation are important for directing the population toward the S* state. The S-2-S-1 internal conversion time was shortened from 135 to 70 fs when going from 485 to 400 nm excitation, as a result of competition between the S-2-S-1 internal conversion from the vibrationally hot S2 state and S2 vibrational relaxation. The S, lifetime of zeaxanthin was within experimental error the same for all excitation wavelengths, yielding similar to 9 ps. No long-lived species have been observed after excitation by femtosecond pulses regardless of the excitation wavelength, but excitation by nanosecond pulses at 266 nm generated both zeaxanthin triplet state and cation radical.
|
|
| 6. |
- Billsten, Helena, et al.
(författare)
-
Photophysical Properties of Xanthophylls in Carotenoproteins from Human Retina.
- 2003
-
Ingår i: Photochemistry and Photobiology. - 0031-8655. ; 78:2, s. 138-145
-
Tidskriftsartikel (refereegranskat)abstract
- The macula of the human retina contains high amounts of the xanthophyll carotenoids lutein and zeaxanthin [a mixture of (3R,3′R)-zeaxanthin and (3R,3′S-meso)-zeaxanthin]. Recently, it was shown that the uptake and the stabilization of zeaxanthin and lutein into the retina are likely to be mediated by specific xanthophyll-binding proteins (XBP). Here, we have used femtosecond pump–probe spectroscopy to study the dynamics of the S1 state of these xanthophylls in xanthophyll-enriched and native XBP. The results from the native XBP and the enriched XBP were then compared with those for carotenoids in organic solvents and in detergent micelles. Steady-state and transient absorption spectra show that the incorporation of xanthophylls into the protein causes a redshift of the spectra, which is stronger for lutein than for zeaxanthin. The transient absorption spectra further indicate that a part of the xanthophylls remains unbound in the xanthophyll-enriched XBP. The transient absorption spectra of the native XBP prove the presence of both xanthophylls in native XBP. Although the S1 lifetime of lutein does not exhibit any changes when measured in solution, micelles or XBP, we have observed the influence of the environment on the S1 lifetime of meso-zeaxanthin, which has a longer (12 ps) lifetime in XBP than in solution (9 ps). The most pronounced effect was found for vibrational relaxation in the S1 state, which is significantly slower for xanthophylls in XBP compared with micelles and solution. This effect is more pronounced for meso-zeaxanthin, suggesting a specific site of binding of this carotenoid to XBP.
|
|
| 7. |
- Billsten, Helena, et al.
(författare)
-
Self-assembled aggregates of the carotenoid zeaxanthin: time-resolved study of excited states
- 2005
-
Ingår i: The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory. - : American Chemical Society (ACS). - 1520-5215. ; 109:8, s. 1521-1529
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we present a way of controlling the formation of the two types of zeaxanthin aggregates in hydrated ethanol: J-zeaxanthin (head-to-tail aggregate, characteristic absorption band at 530 nm) and H-zeaxanthin (card-pack aggregate, characteristic absorption band at 400 run). To control whether J- or H-zeaxanthin is formed, three parameters are important: (1) pH, that is, the ability to form a hydrogen bond; (2) the initial concentration of zeaxanthin, that is, the distance between zeaxanthin molecules; and (3) the ratio of ethanol/water. To create H-aggregates, the ability to form hydrogen bonds is crucial, while J-aggregates are preferentially formed when hydrogen-bond formation is prevented. Further, the formation of J-aggregates requires a high initial zeaxanthin concentration and a high ethanol/water ratio, while H-aggregates are formed under the opposite conditions. Time-resolved experiments revealed that excitation of the 530-nm band of J-zeaxanthin produces a different relaxation pattern than excitation at 485 and 400 run, showing that the 530-nm band is not a vibrational band of the S-2 state but a separate excited state formed by J-type aggregation. The excited-state dynamics of zeaxanthin aggregates are affected by annihilation that occurs in both J- and H-aggregates. In H-aggregates, the dominant annihilation component is on the subpicosecond time scale, while the main annihilation component for the J-a-gregate is 5 ps. The S-1 lifetimes of aggregates are longer than in solution, yielding 20 and 30 ps for H- and J-zeaxanthin, respectively. In addition, H-type aggregation promotes a new relaxation channel that forms the zeaxanthin triplet state.
|
|
| 8. |
- Christensson, Niklas, et al.
(författare)
-
Four-wave-mixing spectroscopy of peridinin in solution and in the peridinin-chlorophyll-a protein
- 2010
-
Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 373:1-2, s. 15-22
-
Tidskriftsartikel (refereegranskat)abstract
- A model for the third order optical response of carotenoids is used to analyse transient grating and pump-probe data of peridinin in solution and bound in the peridinin-chlorophyll protein (PCP). For peridinin in solution, the transient grating signal detected at 505 nm exhibits a bi-exponential recovery whose fast phase is assigned to relaxation from the S-2 state that has a lifetime of 75 +/- 25 fs. The slower, solvent-dependent rise component is assigned to equilibration of the (S-1/ICT) state, taking place on a time scale of 0.6 and similar to 2.5 ps in acetontrile and benzene, respectively. These dynamics match those obtained from pump-probe measured in the spectral region of the ICT state, implying that the ICT state contributes to the signal at 505 nm. In PCP, the transient grating signal shows distinctly different kinetics, and the signal shows no recovery. This difference is explained by energy transfer from peridinin to chlorophyll-a. (C) 2009 Elsevier B. V. All rights reserved.
|
|
| 9. |
- Christensson, Niklas, et al.
(författare)
-
Photon echo spectroscopy reveals structure-dynamics relationships in carotenoids
- 2009
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 79:24
-
Tidskriftsartikel (refereegranskat)abstract
- Based on simultaneous analysis of the frequency-resolved transient grating, peak shift, and echo width signals, we present a model for the third-order optical response of carotenoids including population dynamics and system-bath interactions. Our frequency-resolved photon echo experiments show that the model needs to incorporate the excited-state absorption from both the S-2 and the S-1 states. We apply our model to analyze the experimental results on astaxanthin and lycopene, aiming to elucidate the relation between structure and system-bath interactions. Our analysis allows us to relate structural motifs to changes in the energy-gap correlation functions. We find that the terminal rings of astaxanthin lead to increased coupling between slow molecular motions and the electronic transition. We also find evidence for stronger coupling to higher frequency overdamped modes in astaxanthin, pointing to the importance of the functional groups in providing coupling to fluctuations influencing the dynamics in the passage through the conical intersection governing the S-2-S-1 relaxation.
|
|
| 10. |
- Dietzek, Benjamin, et al.
(författare)
-
Optimal control of peridinin excited-state dynamics
- 2010
-
Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 373:1-2, s. 129-136
-
Tidskriftsartikel (refereegranskat)abstract
- Optimal control is applied to study the excited-state relaxation of the carbonyl-carotenoid peridinin in solution. Phase-shaping of the excitation pulses is employed to influence the photoinduced reaction dynamics of peridinin. The outcome of various control experiments using different experimentally imposed fitness parameters is discussed. Furthermore, the effects of pump-wavelength and different solvents on the control efficiency are presented. The data show that excited-state population within either the S-1 or the ICT state can be reduced significantly by applying optimal control, while the efficiency of control decreases upon excitation into the low-energy side of the absorption band. However, we are unable to alter the ratio of S-1 and ICT population or increase the population of either state compared to excitation with a transform-limited pulse. We compare the results to various control mechanisms and argue that characteristic low-wavenumber modes are relevant for the photochemistry of peridinin. (C) 2010 Elsevier B. V. All rights reserved.
|
|
