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ABSTRACT: Excitation energy transfer in chlorosomes from photosynthetic green sulfur bacteria, Chlorobaculum (Cba.) tepidum and Prosthecochloris (Pst.) aestuarii, have been studied at room temperature by time-resolved femtosecond transient absorption spectroscopy. Bleach rise times from 117 to 270 fs resolved for both chlorosomes reflect extremely efficient intrachlorosomal energy transfer. Bleach relaxation times, from 1 to 3 ps and 25 to 35 ps, probed at 758 nm were tentatively assigned to intrachlorosomal energy transfer based on amplitude changes of the global fits and model calculations. The anisotropy decay constant of about 1 ps resolved at 807 nm probe wavelength for the chlorosomes from Chloroflexus aurantiacus, Pst. aestuarii and Cba. tepidum was related to energy transfer between bacteriochlorophyll a molecules of the baseplate and partly to intrachlorosomal energy transfer. The longer anisotropy components 6.6, 8.8 and 12.1 ps resolved for the three chlorosomes, respectively, were assigned to chlorosome to baseplate energy transfer. Global fits of magic-angle data also revealed longer chlorosome to baseplate energy transfer components from 95 to 135 ps, in accord with results from simulations.
Photochemistry and Photobiology 01/2012; 88(3):675-83. · 2.41 Impact Factor
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ABSTRACT: Simple vacuum evaporation technique for deposition of dyes on various solid
surfaces has been developed. The method is compatible with conventional
solvent-free nanofabrication processing enabling fabrication of nanoscale
optoelectronic devices. Thin films of fluorescein were deposited on glass,
fluorine-tin-oxide (FTO) coated glass with and without atomically layer
deposited (ALD) nanocrystalline 20 nm thick anatase TiO2 coating. Surface
topology, absorption and emission spectra of the films depends on their
thickness and the material of supporting substrate. On a smooth glass surface
the dye initially formes islands before merging into a uniform layer after 5 to
10 monolayers. On FTO covered glass the absorption spectra are similar to
fluorescein solution in ethanol. Absorption spectra on ALD-TiO2 is red shifted
compared to the film deposited on bare FTO. The corresponding emission spectra
at {\lambda} = 458 nm excitation show various thickness and substrate dependent
features, while the emission of films deposited on TiO2 is quenched due to the
effective electron transfer to the semiconductor conduction band.
06/2011;
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ABSTRACT: The halogen bonding between [Ru(dcbpy)(2)(SCN)(2)] dye and I(2) molecule has been studied. The ruthenium complex forms a stable [Ru(dcbpy)(2)(SCN)(2)]···I(2)·4(CH(3)OH) adduct via S···I interaction between the thiocyanate ligand and the I(2) molecule. The adduct can be seen as a model for one of the key intermediates in the regeneration cycle of the oxidized dye by the I(-)/I(3)(-) electrolyte in dye sensitized solar cells.
Chemical Communications 03/2011; 47(15):4499-501. · 6.17 Impact Factor
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ABSTRACT: Exciton model for description of experimentally determined excitation energy transfer from carotenoids to chlorophylls in the LHC-II trimer of spinach is presented. Such an approach allows connecting the excitonic states to the spatial structure of the complex and hence descriptions of advancements of the initially created excitations in space and time. Carotenoids were excited at 490 nm and at 500 nm and induced absorbance changes probed in the Chl Q(y) region to provide kinetic data that were interpreted by using the results from exciton calculations. Calculations included the 42 chlorophylls and the 12 carotenoids of the complex, Soret, Q(x) and Q(y) states of the chlorophylls, and the main absorbing S(2) state of the carotenoids. According to the calculations excitation at 500 nm populates mostly a mixed Lut S(2) Chl a Soret state, from where excitation is transferred to the Q(x) and Q(y) states of the Chl a's on the stromal side. Internal conversion of the mixed state to a mixed Lut S(1) and Chl a Q(y) state provides a channel for Lut S(1) to Chl a Q(y) energy transfer. The results from the calculations support a picture where excitation at 490 nm populates primarily a mixed neoxanthin S(2) Chl b Soret state. From this state excitation from neoxanthin is transferred to iso-energetic Chl b Soret states or via internal conversion to S(1) Chl b Q(y) states. From the Soret states excitation proceeds via internal conversion to Q(y) states of Chl b's mostly on the lumenal side. A rapid Chl b to Chl a transfer and subsequent transfer to the stromal side Chl a's and to the final state completes the process after 490 nm excitation. The interpretation is further supported by the fact that excitation energy transfer kinetics after excitation of neoxanthin at 490 nm and the Chl b Q(y) band at 647 nm (Linnanto et al., Photosynth Res 87:267-279, 2006) are very similar.
Photosynthesis Research 02/2011; 107(2):195-207. · 3.24 Impact Factor
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Liisa Antila,
Mikko Heikkilä,
Ville Mäkinen,
Niko Humalamäki,
Mikko Laitinen,
Veikko Linko,
Pasi Jalkanen,
Jussi Toppari,
Viivi Aumanen,
Marianna Leena Kemell,
Pasi Myllyperkiö,
Karoliina Honkala,
Hannu Häkkinen,
Markku Leskelä, Jouko Korppi-Tommola
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ABSTRACT: Effects of atomic layer deposited (ALD) aluminum oxide barriers on electron injection, recombination reactions, and efficiency of dye-sensitized solar cells were studied. The amorphous AlOx submonolayers prepared on nanocrystalline 2 μm thick TiO2 anatase film were characterized by high-resolution transmission electron microscopy. Time-of-flight elastic recoil detection method was employed to study the growth of similar AlOx layers on planar anatase films. Density functional theory calculations of the first ALD cycle over a (101) anatase surface revealed atomic scale roughness of the deposited layer owing to unequal adsorption sites and lateral repulsions between adsorbed precursor molecules. Calculations also indicate that the holes in the first AlOx layer allow triiodide but not the ruthenium bipyridyl sensitizer to reach the TiO2 surface. After the first deposition cycle the dye binds to AlOx and is in average about 0.2 nm farther from the TiO2 surface than when binding to the bare TiO2 surface. Increase in average distance between the dye and TiO2 surface was considered as the main reason for reduced electron injection efficiency observed for all coated sensitized films. Electrochemical impedance spectroscopy indicated that also recombination reactions of the conduction band electrons with the electrolyte triiodide molecules were reduced. The exponential increase in charge transfer resistance at the dye–TiO2–electrolyte interface as a function of the number of ALD cycles indicated that AlOx barrier layers affect recombination mainly through the tunnel barrier mechanism. Decrease of both the short circuit current and efficiency of the solar cells prepared from above-mentioned films as the number of ALD cycles was increased suggests that the suppression of the recombination could not compensate for the barrier-induced losses of electron injection.
The Journal of Physical Chemistry C 01/2011; 115:16720-16729. · 4.80 Impact Factor
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Liisa Antila,
Mikko Heikkilä,
Ville Mäkinen,
Niko Humalamäki,
Mikko Laitinen,
Veikko Linko,
Pasi Jalkanen,
Jussi Toppari,
Viivi Aumanen,
Marianna Leena Kemell,
Pasi Myllyperkiö,
Karoliina Honkala,
Hannu Häkkinen,
Markku Leskelä, Jouko Korppi-Tommola
The Journal of Physical Chemistry C 01/2011; 115:16720-16729. · 4.80 Impact Factor
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ABSTRACT: Internal dynamics of dansylated poly(propyleneamine) dendrimers (POPAM, G1-G4) in solution and excitation energy transfer from dansyls to eosin in POPAM-eosin complexes have been studied by time-resolved fluorescence spectroscopy and molecular dynamics (MD) simulations. Combining the results from fluorescence anisotropy and the MD simulation studies suggests three time domains for the internal dynamics of the G3 and G4 generations, about 60 ps for motions of the outer-sphere dansyls, 500-1000 ps for restricted motions of back-folded dansyls, and 1500-2600 ps for the overall rotation. For the smaller generations, the contribution from the restricted motions was not entirely evident. Eosin binding hinders fast rotation of the dansyl fragments in the largest G4 dendrimer, but the motion of back-folded dansyls is more hindered in the pure dendrimer. Both fluorescence anisotropy and MD results for the G4 dendrimer support the "soft" dendrimer picture with almost free mobility and substantial back-folding of the dansyls of the dendrimers in solution. Analysis of time-dependent spectral shifts of fluorescence reveals 20-30 ps excited-state solvation relaxation around a single dansyl of a dendrimer. Dendrimer-independent excitation energy transfer from 4 to 8 ps from dansyls to eosins in POPAM-eosin complexes G2-G4 was observed.
The Journal of Physical Chemistry B 02/2010; 114(4):1548-58. · 3.70 Impact Factor
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ABSTRACT: Electron transfer from three conjugated amino-phenyl acid dyes to titanium and aluminum oxide nanocrystalline films was studied by using transient absorption spectroscopy with sub 20 fs time-resolution over the visible spectral region. All the dyes attached to TiO2 showed long-lived ground state bleach signals indicative of formation of new species. Global analysis of the transient kinetics of the dyes on TiO2 revealed stimulated emission decays of about 40 fs and less than 300 fs assigned to electron injection. The same dyes on Al2O3 substrates displayed long stimulated emission decays (ns) suggesting that electron transfer is blocked in this high band gap semiconductor. For two of the dyes (NK1 and NK2) with amino methyl terminal groups cation formation was seen at 670 nm probe wavelength, in the onset region of cation absorption predicted by time-dependent density functional theory calculations, with dynamics matching that of stimulated emission decay. Early excited-state dynamics observed in the NK7 dye bound to both TiO2 and Al2O3, with pulse limited rise and 30−40 fs decay times, was assigned to rearrangement of charge in the amino phenyl moiety and/or possibly isomerization, which competes with electron injection in NK7 sensitized TiO2 films. This additional relaxation channel could be the reason for the low efficiency reported for the NK7 sensitized solar cell.
07/2009;
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ABSTRACT: Chlorosomes from green photosynthetic bacteria Chloroflexus aurantiacus have been studied by timeresolved
femtosecond transient absorption spectroscopy. The fastest kinetics of 200–300 fs resolved,
was interpreted to stem for intra-chlorosomal excitation energy transfer. Energy transfer from the
antenna to the baseplate appeared as a major 9.2 ps rise component detected at the baseplate probe
wavelength. Excitation energy transfer rates were evaluated for a model chlorosome. Calculated rod to
rod, and rods to baseplate rate constants of 200–400 fs and 10–20 ps, respectively, are in accord with
the experimental results.
Chemical Physics Letters 01/2009; 477:216. · 2.34 Impact Factor
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ABSTRACT: Grooves were etched in a conductive layer of a conductive, transparent glass, and a nanoporous TiO2 film was deposited on both the conductive and nonconductive area. The width of the grooves was 100 $\mu$m and 150 $\mu$m. A transparent TiO2 film was dye-sensitized, covered with an electrolyte, and sandwiched with a cover glass. The conductivity of the dye-sensitized TiO2 film permeated with electrolyte was studied in the dark and under illumination, and was observed to be dependent on light intensity, wavelength and applied voltage. This study shows that dye-sensitized nanoporous films can be used as a wavelength dependent photoconductor.
04/2008;
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ABSTRACT: Excited state dynamics and electron transfer from the Ru(dcbpy)2(NCS)2 (RuN3) sensitizer to semiconductor nanoparticles were studied using time-resolved femtosecond absorption spectroscopy. We found that excitation of the red wing of the absorption spectrum of the sensitizer populates the (3)MLCT state directly, both in solution and attached on semiconductor nanoparticle films. Electron injection is slowed down and becomes gradually less efficient as excitation moves towards red from the absorption maximum at 535 nm. At 675 nm the injection is non-exponential and characterized by 5, 30 and 180 ps time constants. The non-exponential electron injection observed is assigned to injection from a distribution of triplet states with energies below the semiconductor conduction band edge.
Physical Chemistry Chemical Physics 03/2008; 10(7):996-1002. · 3.57 Impact Factor
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ABSTRACT: We report a pump-probe experiment revealing the temporal evolution of subpicosecond evolution of Prodan's excited-state absorption in dimethylformamide. Also, we present calculation of the first spectral moment of this spectral band and estimation of different relaxation components on the subpicosecond time scale.
Annals of the New York Academy of Sciences 02/2008; 1130:52-5. · 3.15 Impact Factor
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ABSTRACT: A new dye-sensitized solar cell driven electrochromic device has been fabricated. The device consists of an electrochromic display and a solar cell in a single nanocrystalline film. The optimization of the electrochromic and the solar cell functions was carried out. An applied potential of 1.0 V was required for coloring and the best solar energy conversion efficiency 1.1% was achieved. The efficiency may be compared to an efficiency of 4.6% obtained in a similar dye-sensitized solar cell without the display property. Coloring and bleaching times of the device were less than one second and a transmittance change from 38.7% (bleached) to 15.9% (colored) at best was achieved. The optimization of the electrochromic property of the device lead to decreasing efficiency of the solar cell and vice versa.
Photochemical and Photobiological Sciences 02/2007; 6(1):63-6. · 2.58 Impact Factor
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ABSTRACT: The synthesis, X-ray crystal structures and spectroscopic characterization (UV-Vis absorption and fluorescence emission) of regioselective tetradansylated resorcinarene 2 and octadansylated resorcinarene 3 are described. In solution, the resorcinarene backbone of 2 shows a boat conformation with C2v symmetry, while the octasubstituted 3 shows at room temperature a time-averaged C4v symmetry, which turns into stable boat conformation at low temperatures. The four hydroxyl groups of 2, not present in 3, form hydrogen bonds to the sulfoxide oxygens of the dansyl moieties and stabilize the C2v conformation in solution. The X-ray crystal structures of 2 and 3 confirm the C2v symmetry of both compounds in the crystalline state and revealed that the tetradansyl resorcinarene has two rather strong intramolecular O-HO[double bond, length as m-dash]S hydrogen bonds. In addition 2 forms a directly hydrogen-bonded dimeric assembly via four intermolecular O-HO and O-HO[double bond, length as m-dash]S hydrogen bonds
New Journal of Chemistry 01/2007; 31:370-376. · 2.61 Impact Factor
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ABSTRACT: Four new quaternary ammonium iodides, (Me2Pe2N)I, (Me2Hex2N)I, (Et2Pe2N)I and (Et2Hex2N)I, were synthesized and studied as electrolytes for dye-sensitized solar cells. All compds. were solids at room temp. The influence of varying amts. of elemental I and the effect of tert-butylpyridine (TBP) on the performance of a cell was also studied. Addn. of I lowered the m.ps. of the polyiodides. Of the NH4+ iodides only (Me2Hex2N)I:I2 (10:1) was liq. at room temp. and the others were soft solids. Under illumination from a halogen lamp at 10 mW/cm2, the highest power conversion efficiency of 2.4% was obtained with (Me2Hex2N)I:I2 (10:1) liq. electrolyte contg. TBP. This may be compared to an efficiency of 5.4% obtained from similar cells with traditional 3-methoxypropionitrile based electrolyte tested under identical conditions. The best efficiency with the soft solid electrolyte, (Et2Hex2N)I:I2 (10:1) with TBP, was 2.3%. [on SciFinder(R)]
Journal of Photochemistry and Photobiology A Chemistry 01/2007; 186(1):29-33. · 2.42 Impact Factor
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ABSTRACT: Energy transfer of the light harvesting complex LHC-II trimer, extracted from spinach, was studied in the Q(y) region at room temperature by femtosecond transient absorption spectroscopy. Configuration interaction exciton method [Linnanto et al. (1999) J Phys Chem B 103: 8739-8750] and 2.72 A structural information reported by Liu et al. was used to calculate spectroscopic properties and excitation energy transfer rates of the complex. Site energies of the pigments and coupling constants of pigment pairs in close contact were calculated by using a quantum chemical configuration interaction method. Gaussian random variation of the diagonal and off-diagonal exciton matrix elements was used to account for inhomogeneous broadening. Rate calculations included only the excitonic states initially excited and probed in the experiments. A kinetic model was used to simulate time and wavelength dependent absorption changes after excitation on the blue side of the Q(y) transition and compared to experimentally recorded rates. Analysis of excitonic wavefunctions allowed identification of pigments initially excited and probed into later. It was shown that excitation of the blue side of the Q(y) band of a single LHC-II complex results in energy transfer from chlorophyll b's of the lumenal side to chlorophyll a's located primarly on one of the monomers of the stromal side.
Photosynthesis Research 04/2006; 87(3):267-79. · 3.24 Impact Factor
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ABSTRACT: The present review describes the use of quantum chemical methods in estimation of structures and electronic transition energies of photosynthetic pigments in vacuum, in solution and imbedded in proteins. Monomeric Mg-porphyrins, chlorophylls and bacteriochlorophylls and their solvent 1:1 and 1:2 complexes were studied. Calculations were performed for Mg-porphyrin, Mg-chlorin, Mg-bacteriochlorin, mesochlorophyll a, chlorophylls a, b, c(1), c(2), c(3), d and bacteriochlorophylls a, b, c, d, e, f, g, h, plus several homologues. Geometries were optimised with PM3, PM3/CISD, PM5, ab initio HF (6-31G*/6-311G**) and density functional B3LYP (6-31G*/6-311G**) methods. Spectroscopic transition energies were calculated with ZINDO/S CIS, PM3 CIS, PM3 CISD, ab initio CIS, time-dependent HF and time-dependent B3LYP methods. Estimates for experimental transition energies were obtained from linear correlations of the calculated transition energies of 1:1 solvent complexes against experimentally recorded solution energies (scaling). According to the calculations in five-coordinated solvent complexes the magnesium atom lies out of the porphyrin plane, while in six-coordinated complexes the porphyrin is nearly planar. Charge densities on magnesium and nitrogen atoms were strongly dependent on the computational method deployed. Several dark states of low oscillator strength below the main Soret band were predicted for solvent complexes and chlorophylls and bacteriochlorophylls in protein environment. Such states, though not yet identified experimentally, might serve as intermediate states for excitation energy transfer in photosynthetic complexes. Q(y), Q(x) and Soret transition energies were found to depend on the orientation of the acetyl group and external pressure. A method to estimate site energies and dimeric interaction energies and to simulate absorption and CD spectra of photosynthetic complexes is described. Simulations for the light harvesting complexes Rhodospirillum molischianum, chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, and LHC-II of Spinacia oleracea are presented as examples.
Physical Chemistry Chemical Physics 03/2006; 8(6):663-87. · 3.57 Impact Factor
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ABSTRACT: Mechanisms of the light-induced ligand exchange reaction of (trans-I) Ru(dcbpy)(CO)2I2 (dcbpy = 4,4'-dicarboxylic acid-2,2'-bipyridine) in ethanol have been studied by transient absorption spectroscopy. Ultraviolet 20 fs excitation pulses centered at 325 nm were used to populate a vibrationally hot excited pi bipyridyl state of the reactant that quickly relaxes to a dissociative Ru-I state resulting in the release of one of the carbonyl groups. Quantum yield measurements have indicated that about 40% of the initially exited reactant molecules form the final photoproduct. A 62 fs rise component in the transient absorption (TA) signal was observed at all probe wavelengths in the visible region for the ongoing reaction, while the rise for the photoproduct was pulse limited (20 fs). We assign the observed 62 fs time component to the depopulation of the repulsive CO dissociative state. Vibrational coherences of the TA signals were observed at a wavenumber of 90 cm(-1). The resolved frequency, typical of I-Ru-I vibrational modes, is assigned to trans-cis isomerization of the iodines of the five-coordinated intermediate and damping of this oscillation in 500 fs to simultaneous solvent coordination. Cooling of the hot reactant and the product molecules occurs on a much slower time scale from 4 to 270 ps (Lehtovuori, V.; Aumanen, J.; Myllyperkiö, P.; Rini, M.; Nibbering, E. T. J.; Korppi-Tommola, J. J. Phys. Chem. A 2004, 108, 1644).
The Journal of Physical Chemistry B 10/2005; 109(37):17538-44. · 3.70 Impact Factor
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ABSTRACT: Optical absorption, fluorescence, and quantitative 13C NMR spectroscopy have been used to study the degradation of mineral gearbox oil. Samples of used oil were collected from field service. Measured absorption, fluorescence, and quantitative 13C NMR spectra of used oils show characteristic changes from the spectra of a fresh oil sample. A clearly observable, approximately 20-nm blueshift of the fluorescence emission occurs during the early stages of oil use and correlates with changes in intensity of some specific 13C NMR resonance lines. These changes correlate with oil age because of the connection between the blueshift and breaking of the larger conjugated hydrocarbons of oil as a result of use.
Applied Optics 09/2004; 43(24):4718-22. · 1.41 Impact Factor
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ABSTRACT: Ab initio HF/6-31G* and density functional B3LYP/6-31G* methods have been used to calculate fully optimized structures of methyl bacteriochlorophyllides a, b, g, and h and magnesium-bacteriochlorin. Semiempirical ZINDO/S CIS and ab initio CIS/6-31G* and CIS/6-311G** configuration interaction methods and time dependent HF/6-31G*, HF/6-311G**, B3LYP/6-31G*, and B3LYP/6-311G** methods were used to estimate corresponding spectroscopic transition energies of the chromophores. The effects of solvent coordination were also studied by optimizing structures of 1:1 complexes of the methyl bacteriochlorophyllides and acetone. The self-consistent reaction field model was used to estimate bulk solvent effects. Differences in B3LYP and HF bond lengths of the bacteriochlorin had a strong influence on the calculated transition energies. Large variations of calculated transition energies were also observed when coordinates from different X-ray structure determinations were used for the same pigment. In the five coordinated solvent complex, the Mg atom is shifted from the bacteriochlorin plane, inducing red shifts of the Qx and Soret transitions. Linear correlations of the calculated and experimental solution transition energies were obtained with characteristic slopes and intercepts for each method used, reflecting inadequacy of the methods to describe transition energies in bacteriochlorins. Such correlations were shown to be useful in prediction of site transition energies for a pigment (pigment group) in solution or in protein under a given computational approach. Best correlations and the best calculated transition energies were obtained by using the ZINDO/S CIS method with B3LYP/6-31G* optimized structures. Calculations suggested the existence of a number of dark electronic states of bacteriochlorophylls below the main Soret transition. The density of these states was dependent on pigment surroundings. Dark states may have an important role in carotenoid to chlorophyll or to bacteriochlorophyll energy transfer in photosynthetic light harvesting complexes. It was also shown that conformation of an acetyl group of methyl bacteriochlorophyll a has an effect on calculated transition energies.
The Journal of Physical Chemistry A 06/2004; 108:5872. · 2.95 Impact Factor
