| 1. |
- Braumueller, Markus, et al.
(författare)
-
Synthesis and characterization of an immobilizable photochemical molecular device for H-2-generation
- 2015
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 44:12, s. 5577-5586
-
Tidskriftsartikel (refereegranskat)abstract
- With [Ru-II(bpyMeP)(2)tpphzPtCl(2)](2+) (4) a molecular photocatalyst has been synthesized for visible-light-driven H-2-evolution. It contains the ligand bpyMeP (4,4'-bis(diethyl-(methylene)-phosphonate)-2,2'-bipyridine) with phosphate ester groups as precursors for the highly potent phosphonate anchoring groups, which can be utilized for immobilization of the catalyst on metal-oxide semiconductor surfaces. The synthesis was optimized with regard to high yields, bpyMeP was fully characterized and a solid-state structure could be obtained. Photophysical studies showed that the photophysical properties and the localization of the excited states are not altered compared to similar Ru-complexes without anchoring group precursors. (4) was even more active in homogenous catalysis experiments than [RuII(tbbpy)(2)tpphzPtCl(2)](2+) (6) with tbbpy (4,4'-bis(tbutyl)-2,2'-bipyridine) as peripheral ligands. After hydrolysis (4) was successfully immobilized on NiO, suggesting that an application in photoelectrosynthesis cells is feasible.
|
|
| 2. |
- Christensson, Niklas, et al.
(författare)
-
Probing the strength of the system-bath interaction by three-pulse photon echoes.
- 2009
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:2
-
Tidskriftsartikel (refereegranskat)abstract
- We explore how the width of the three-pulse photon echo signal at long population times can be used to determine the strength of the system-bath interaction. Using simulation with finite pulses we show that a simple relation exist between the width of the echo signal, the coupling strength, and the pulse autocorrelation. The derived model is applied to Rhodamine 6G in alcoholic solution, a paradigm system for the study of solvation dynamics, and the results are compared to conventional methods. The independently determined coupling strength forms the basis for a computationally inexpensive route to determine the entire spectral density, the key parameter when considering system-bath interactions. Our method allows us to accurately estimate the relative amplitude of fast and slow components in the correlation function using only impulsive limit simulations. We show that the peak shift significantly overestimates the amplitude of the fastest decay component for our experimental data. Changing solvent from methanol to 1-hexanol we observe a narrowing of the width of the echo profile. The changes in the echo width allow us to estimate the changes of the coupling strength in various solvents.
|
|
| 3. |
- Christensson, Niklas, et al.
(författare)
-
Solute specific polar solvation studied by photon echo spectroscopy
- 2009
-
Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 357:1-3, s. 85-95
-
Tidskriftsartikel (refereegranskat)abstract
- Polar solvation dynamics Of two Solute molecules in a series of 1-alcohols has been studied using the three-pulse photon echo peak shift technique. The inertial dynamics, on sub-200 fs timescale, is essentially independent of solvent in the 1-alcohol series. For a given solute, the solvent dependence is mainly manifested in the diffusive solvation dynamics. The solute dependence appears as a significantly stronger inertial component in one of the molecules. We ascribe this solute dependence to the differences in charge redistribution upon excitation. A detailed investigation of oscillations of the peak shift reveals a solvent dependent beating that can be connected to solvation of the vibrational mode in the excited state. The solvent dependence of the dephasing dynamics of the excited state mode can be explained by the electronic transition frequency correlation function and the beating pattern of the echo signal originates from interference between ground and excited state Feynman pathways. (C) 2008 Elsevier B.V. All rights reserved.
|
|
| 4. |
- Christensson, Niklas, et al.
(författare)
-
Three-pulse photon echo peak shift in optically dense samples
- 2008
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 457:1-3, s. 106-109
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the dependence of the three-pulse photon echo peak-shift (3PEPS) signal on solute concentration and sample path length. The most prominent effect is an increase of the amplitude of the long decay component of the 3PEPS at high optical densities, but signal distortions are observed for all timescales in the experiments. The distortions of the peak shift signal are more severe for longer path lengths. These observations are assigned to pulse propagation effects. At low concentrations interference between the solute signal and the non-resonant solvent response severely distort the peak profiles at short population times.
|
|
| 5. |
- De la Cadena, Alejandro, et al.
(författare)
-
Intermolecular exciton-exciton annihilation in phospholipid vesicles doped with [Ru(bpy)(2)dppz](2+)
- 2016
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 644, s. 56-61
-
Tidskriftsartikel (refereegranskat)abstract
- The ultrafast photophysics of [Ru(bpy)(2)dppz](2+) (dppz = dipyrido[3,2-a:2',3'-c]-phenazine) embedded into the walls of phospholipid vesicles has been studied by femtosecond time-resolved pump-probe spectroscopy. While [Ru(bpy)(2)dppz](2+) has been studied intensively with respect to its intramolecular charge transfer processes, which are associated with the well known light-switch effect, this study focuses on intermolecular energy transfer processes taking place upon dense packing of the complexes into a phospholipid membrane composed of dipalmitoyl-t-a-phosphatidylglycerol, which can be thought of as a simplistic model of a cellular membrane. The data indicate additional quenching of excited [Ru(bpy)(2)dppz](2+) upon increasing the pump-pulse intensity. Hence, the observed photophysics, which is assigned to the presence of intermolecular exciton-exciton annihilation at high pump-intensities, might be related to the ultrafast photophysics of [Ru(bpy)(2)dppz](2+) when used as a chromophore to stain cells, an effect that may be taken into account during the employment of novel cellular markers based on Ru polypyridine complexes. (C) 2015 Elsevier B.V. All rights reserved.
|
|
| 6. |
- Dietzek, Benjamin, et al.
(författare)
-
Appearance of coherent artifact signals in femtosecond transient absorption spectroscopy in dependence on detector design
- 2007
-
Ingår i: Laser Physics Letters. - : IOP Publishing. - 1612-2011 .- 1612-202X. ; 4:1, s. 38-43
-
Tidskriftsartikel (refereegranskat)abstract
- The appearance of coherent artifact signals in transient absorption spectroscopy employing a spectrally integrated detection system is studied. The influence of the detection design on the shape of the observed signal is detailed and the experimentally very important case, in which the shape of the coherent artifact is strongly influenced by the presence of the sample itself, is considered - leading to the situation that the artifact signal cannot be accounted for by simple comparison of the kinetics obtained for the solvent only. Finally an estimate of the relative contribution of the artifact to the overall transient absorption change is presented facilitating the interpretation of short time transients in the presence of artifact contributions and allowing to estimate the excited state absorption cross-section for a known pump-intensity dependence of the artifact signal.
|
|
| 7. |
- Dietzek, Benjamin, et al.
(författare)
-
Appearance of intramolecular high-frequency vibrations in two-dimensional, time-integrated three-pulse photon echo data
- 2007
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 9:6, s. 701-710
-
Tidskriftsartikel (refereegranskat)abstract
- An alternative experimental outline to measure homodyne detected three-pulse photon-echo data is presented. The novel experimental approach allowing for online monitoring and correction of experimental timing and stability is discussed in detail using the paradigm system of Nile blue in alcohol solution. It is shown that excellent signal-to-noise ratios together with high reproducibility of the data can be routinely achieved. We report in detail on the appearance of high-frequency intramolecular vibrations in the two-dimensional three-pulse photon-echo data and suggest that besides the conventionally discussed three-pulse photon-echo peak-shift the width of the integrated echo signal as a function of population time contains identical and easily accessible information on high-frequency intramolecular vibrations. A comparison of experimental data with theoretical modeling is performed showing that the observed echo-width oscillations are in line with predictions of the Brownian oscillator model.
|
|
| 8. |
- Dietzek, Benjamin, et al.
(författare)
-
Control of a chemical reaction far from the Franck-Condon point by single-pulse resonant and non-resonant light-matter interaction.
- 2007
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 129:43, s. 13014-13021
-
Tidskriftsartikel (refereegranskat)abstract
- Using optimal control as a spectroscopic tool we decipher the details of the molecular dynamics of the essential multidimensional excited-state photoisomerization - a fundamental chemical reaction of key importance in biology. Two distinct nuclear motions are identified in addition to the overall bond-twisting motion: Initially, the reaction is dominated by motion perpendicular to the torsion coordinate. At later times, a second optically active vibration drives the system along the reaction path to the bottom of the excited-state potential. The time scales of the wavepacket motion on a different part of the excited-state potential are detailed by pump-shaped dump optimal control. This technique offers new means to control a chemical reaction far from the Franck-Condon point of absorption and to map details of excited-state reaction pathways revealing unique insights into the underlying reaction mechanism.
|
|
| 9. |
- Dietzek, Benjamin, et al.
(författare)
-
Dynamics of charge separation in the excited-state chemistry of protochlorophyllide
- 2010
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 492:1-3, s. 157-163
-
Tidskriftsartikel (refereegranskat)abstract
- In this study the excited-state dynamics of protochlorophyllide a (PChlide), the substrate of the enzyme protochlorophyllide oxidoreductase, was examined by means of time-resolved absorption anisotropy and magic-angle measurements. The solvent polarity dependent anisotropy data provide strong evidence for the existence of an excited-state with charge-transfer character. A solvent dependency is also observed in the magic-angle kinetics. In a nonpolar environment wave packet oscillations are monitored while they are quenched in a polar solvent. These results show that the excited-state relaxations of PChlide are determined by the nature of the solvent environment. The implications of these findings are discussed with respect to the enzyme catalysed reaction. (C) 2010 Elsevier B. V. All rights reserved.
|
|
| 10. |
- Dietzek, Benjamin, et al.
(författare)
-
Excited-state dynamics of Ru(tbbpy)(3)(2+) investigated by femtosecond time-resolved four-wave mixing
- 2007
-
Ingår i: Laser Physics Letters. - : IOP Publishing. - 1612-2011 .- 1612-202X. ; 4:2, s. 121-125
-
Tidskriftsartikel (refereegranskat)abstract
- Femtosecond time-resolved two-color four-wave mixing is employed to study the ultrafast excited-state relaxation processes in Ru(tbbpy)(3)(+2). The relaxation processes leading to a long-lived thermalized (MLCT)-M-3-state are found to take place on two distinct time-scales. An ultrafast process, which is attributed to intersystem crossing, rapidly depopulating the initially photoexcited (MLCT)-M-1-state, is found to take place in less than 200 fs. The second process visible in the experimental data occurs on a picosecond time-scale and is assigned to cooling within the (MLCT)-M-3-state.
|
|
| 11. |
- Dietzek, Benjamin, et al.
(författare)
-
Experimental observation of different-order components of a vibrational wave packet in a bulk dielectric using high-order Raman scattering
- 2007
-
Ingår i: Physical Review Letters. - 1079-7114. ; 98:18
-
Tidskriftsartikel (refereegranskat)abstract
- We use high-order Raman scattering in a bulk dielectric to characterize coherent dynamics with precision typical for gas phase experiments. The experimental pump-probe approach allows for the simultaneous observation and separation in space and time of the individual contributions of different-order Raman processes to a coherent wave packet without relying on phase-matching conditions and within the same experimental geometry. We propose a novel technique to discriminate between stimulated excitation of vibronic levels in the impulsive and intermediate excitation regimes, futhermore allowing us to distinguish between different pathways contributing to the same fifth-order Raman processes.
|
|
| 12. |
- Dietzek, Benjamin, et al.
(författare)
-
Mechanisms of molecular response in the optimal control of photoisomerization
- 2006
-
Ingår i: Physical Review Letters. - 1079-7114. ; 97:25
-
Tidskriftsartikel (refereegranskat)abstract
- We report on adaptive feedback control of photoinduced barrierless isomerization of 1,1'-diethyl-2,2'-cyanine in solution. We compare the effect of different fitness parameters and show that optimal control of the absolute yield of isomerization (photoisomer concentration versus excitation photons) can be achieved, while the relative isomerization yield (photoisomer concentration versus number of relaxed excited-state molecules) is unaffected by adaptive feedback control. The temporal structure of the optimized excitation pulses allows one to draw clear mechanistic conclusions showing the critical importance of coherent nuclear motion for the control of isomerization.
|
|
| 13. |
- Dietzek, Benjamin, et al.
(författare)
-
On the excited-state multi-dimensionality in cyanines
- 2008
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 455:1-3, s. 13-19
-
Tidskriftsartikel (refereegranskat)abstract
- Vibrational coherences in a photoexcited cyanine dye are preserved for the time-scale of diffusive torsional motion to the bottom of the excited-state potential. The coherently excited modes are virtually unaffected by solvent friction and thus distinct from the bond-twisting motion, which is strongly coupled to the surrounding solvent. We correlate the modes apparent in the resonance Raman and the four-wave mixing signal of 1,1'-diethyl-2,2'-cyanine with the understanding of optimal control of isomerization. In turn, the experimental results illustrate that optimal control might be used to obtain vibrational information complementary to conventional spectroscopic data.
|
|
| 14. |
- 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.
|
|
| 15. |
- Dietzek, Benjamin, et al.
(författare)
-
Protochlorophyllide a: A Comprehensive Photophysical Picture
- 2009
-
Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 10:1, s. 144-150
-
Tidskriftsartikel (refereegranskat)abstract
- The photochemistry of protochlorophyllide a, a precursor in the biosynthesis of chlorophyll and substrate of the light regulated enzyme protochlorophyllide oxidoreductase, is investigated by pump-probe spectroscopy. Upon excitation into the lowest lying Q-band the light induced changes ore recorded over a wide range of probe wavelengths in the visible and near-IR region between 500 and 1000 nm. Following excitation, an initial ultrafast 450 Is process is observed related to the motion out of the Franck-Condon region on the excited state surface; thus directly unraveling previous suggestions based on time-resolved fluorescence measurements (ChemPhysChem 2006, 7, 1727-1733). Furthermore, the data reveals a previously concealed photointermediate, whose formation on a nanosecond timescale matches the overall fluorescence decay and is assigned to a triplet state. The implications of this finding with respect to the photochemistry of NADPH.-protochlorophyllide oxidoreductase (POR) ore discussed.
|
|
| 16. |
- Dietzek, Benjamin, et al.
(författare)
-
The excited-state chemistry of protochlorophyllide a: A time-resolved fluorescence study
- 2006
-
Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 7:8, s. 1727-1733
-
Tidskriftsartikel (refereegranskat)abstract
- The excited-state processes of protochlorophyllide a, the precursor of chlorophyll a in chlorophyll biosynthesis, are studied using picosecond time-resolved fluorescence spectroscopy. Following excitation into the Soret band, two distinct fluorescence components, with emission maxima at 640 and 647 nm, ore observed. The 640 nm emitting component appears within the time resolution of the experiment and then decays with a time constant of 27 ps. In contrast, the 647 nm emitting component is built up with a 3.5 ps rise time and undergoes a subsequent decay with a time constant of 3.5 ns. The 3.5 ps rise kinetics are attributed to relaxations in the electronically excited state preceding the nanosecond fluorescence, which is ascribed to emission out of the thermally equilibrated S, state. The 27 ps fluorescence, which appears within the experimental response of the streak camera, is suggested to originate from a second minimum on the excited-state potentiol-energy surface. The population of the secondary excited state is suggested to reflect a very fast motion out of the Franck-Condon region along a reaction coordinate different from the one connecting the Franck-Condon region with the S-1 potential-energy minimum. The 27 ps-component is an emissive intermediate on the reactive excited-state pathway, as its decay yields the intermediate photoproduct, which has been identified previously (J. Phys. Chem. B 2006, 110, 4399-4406). No emission of the photoproduct is observed. The results of the time-resolved fluorescence study allow a detailed spectral characterization of the emission of the excited states in protochlorophyllide a, and the refinement of the kinetic model deduced from ultrafast absorption measurements.
|
|
| 17. |
- Dietzek, Benjamin, et al.
(författare)
-
Tracking ultrafast excited-state bond-twisting motion in solution close to the Franck-Condon point
- 2007
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 111:21, s. 6034-6041
-
Tidskriftsartikel (refereegranskat)abstract
- Applying optimal control to photoinduced trans-cis isomerization in condensed phase, the dynamics of bond-twisting motion of 1,1'-diethyl-4,4'-cyanine in methanol and propanol is revealed. The shape of the optimized pulse resulting from minimization of the photoisomer formation can be directly related to the initial excited-state dynamics in close proximity to the Franck-Condon point. The solvent viscosity-dependent ultrafast wavepacket motion is reflected in the prominent down-chirp of the optimized pulses and reveals a detailed picture of the control mechanism: The reduction of the isomer production is achieved by most efficient dumping of excited population back to the trans ground state. In the higher-viscosity solvent, propanol, wavelength-dependent oscillatory features are superimposed to the overall chirp structure pointing to the importance of excited-state vibrational coherences for the dumping process.
|
|
| 18. |
- Dietzek, Benjamin, et al.
(författare)
-
Ultrafast excited-state isomerization dynamics of 1,1 '-diethyl-2,2 '-cyanine studied by four-wave mixing spectroscopy
- 2007
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 111:19, s. 5396-5404
-
Tidskriftsartikel (refereegranskat)abstract
- Excited-state dynamics and solvent-solute interactions of 1,1'-diethyl-2,2'-cyanine iodine (1122C) in alcoholic solutions are investigated using time-integrated three-pulse photon-echo spectroscopy. 1122C serves as a model compound for ultrafast photoinduced isomerizationa key process in the light reception of plants, bacteria, and human vision. The photoreaction in 1122C is interrogated in dependence on solvent and excitation wavelength. The wavelength-dependent three-pulse photon-echo peak shift indicates strong alterations of the reaction pathways and points to the existence of a direct internal conversion channel in close proximity to the Franck-Condon point of absorption. The solvent-dependent S-1-S-0 internal conversion time does not follow conventional sheared viscosity dependence, suggesting that the solvent local friction has to be considered to account for the observed isomerization kinetics. The concerted discussion of transient grating and three-pulse photon-echo peak-shift data allows us to derive a complete picture of the solvent-solute interaction-controlled photoreaction. The results obtained are related to other work on reactive systems and are discussed in the framework of multilevel response functions.
|
|
| 19. |
- Dietzek, Benjamin, et al.
(författare)
-
Visualizing overdamped wavepacket motion: Excited-state isomerization of pseudocyanine in viscous solvents
- 2009
-
Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 357:1-3, s. 54-62
-
Tidskriftsartikel (refereegranskat)abstract
- The isomerization of 1,1'-diethyl-2,2'-cyanine iodide in n-alcohols is studied by femtosecond pump-probe spectroscopy. Using a broad range of probe wavelengths, the dynamics of ground-state bleach recovery, excited-state absorption and stimulation emission are monitored. We attributed the observed spectral evolution to the excited-state torsional motion, which occurs in a barrierless fashion in all solvents investigated. Excitation initiates a fast downhill bond-twisting motion on steep part of the S, potential. The rate-limiting step of the isomerization is the stochastic bond twisting on a relatively flat part of the potential at the bottom of S-1. The dependences of the bond-twisting rates on solvent viscosity are different for the steep and flat parts of the S, potential. To the best of out knowledge, this work constitutes the first experimental observation of a process for which the viscosity dependence of the reaction rate changes along the reaction coordinate. (C) 2008 Elsevier B.V. All rights reserved.
|
|
| 20. |
- Dietzek, Benjamin, et al.
(författare)
-
Watching ultrafast barrierless excited-state isomerization of pseudocyanine in real time
- 2007
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 111:17, s. 4520-4526
-
Tidskriftsartikel (refereegranskat)abstract
- The photoinduced excited-state processes in 1,1'-diethyl-2,2'-cyanine iodine are investigated using femtosecond time-resolved pump-probe spectroscopy. Using a broad range of probe wavelengths, the relaxation of the initially prepared excited-state wavepacket can be followed down to the sink region. The data directly visualize the directed downhill motion along the torsional reaction coordinate and suggest a barrierless excited-state isomerization in the short chain cyanine dye. Additionally, ultrafast ground-state hole and excited-state hole replica broadening is observed. While the narrow excited-state wavepacket broadens during pump-probe overlap, the ground-state hole burning dynamics takes place on a significantly longer time-scale. The experiment reported can be considered as a direct monitoring of the shape and the position of the photoprepared wavepacket on the excited-state potential energy surface.
|
|
| 21. |
- Dietzek, Benjamin, et al.
(författare)
-
Wavelength-dependent photoproduct formation of phycocyanobilin in solution - Indications for competing reaction pathways
- 2011
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 515:1-3, s. 163-169
-
Tidskriftsartikel (refereegranskat)abstract
- Phycocyanobilin (PCB), an open-chain tetrapyrrole, makes up - slightly modified - the chromophore in phytochromes, the importance of which triggered model studies on the photochemistry of PCB in solution. We use pump-wavelength dependent femtosecond transient absorption spectroscopy including the near-IR region for probing to gain new insight into the photoreaction. The data reveal the coexistence of three ground state species: The dominant species PCBA undergoes photoreaction into PCBB and PCBC indicating a branching of the initial reaction path leading to formation of PCBB and PCBC. On this basis the photoreaction involves fast structural rearrangements within the tetrapyrrolic macrocycle, which are followed by slower rate-limiting changes in the protonation state of the pyrrolenine/pyrrole rings. (C) 2011 Elsevier B.V. All rights reserved.
|
|
| 22. |
- Föhlinger, Jens
(författare)
-
Shining Light on Molecules : Electron Transfer Processes in Model Systems for Solar Energy Conversion Investigated by Transient Absorption Spectroscopy
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the recent years, solar energy conversion has attracted a huge research interest due to the potential application for limiting the greenhouse effect. In many solar cells and solar fuel cells, understanding of charge transfer (CT) and recombination is important for future improvement of the overall efficiency. One important tool for that is transient absorption spectroscopy (TAS).Mesoporous nickel oxide films were investigated due to their potential application in p-type dye-sensitized solar cells (DSSCs), tandem DSSCs and dye sensitized solar fuel cells (DSSFC:s). Firstly, it was found that the hole generated by band gap excitation is trapped on an ultrafast time scale by Ni3+ states. It was possible to observe a direct signal from the holes by transient mid-IR absorption spectroscopy allowing for direct detection of hole injection and trapping. On a ns time scale, the trapped holes relaxed to much less reactive holes which favored long lived NiO-dye charge separation (CS).A series of perylene monoimide (PMI) dyes with different anchoring groups was studied. Differences in binding affinity and stability were found. Nevertheless, all PMIs showed ultrafast charge separation and similar recombination kinetics. Furthermore, the effect of MLCT localization of ruthenium polypyridyl complexes was investigated. All those dyes showed slow or no hole injection. At the same time, a self-quenching process was found for all compounds that limited the photoconversion efficiency.Furthermore, a new core-shell structure of p-type DSSCs was proposed and investigated. Here, the liquid electrolyte was replaced by a layer of TiO2. That system was found to undergo both injection and regeneration of the dye on an ultrafast time scale (below 1 ps). Furthermore, the CS state did not show any decay within 2 ns making this structure interesting for application in DSSCs.A pentad consisting of a known Ru-based (electro)chemical water oxidation catalyst (WOC) linked to two zinc-porphyrin-fullerene dyads (ZnP-C60) was investigated. The charge transfer processes leading to the first oxidation of the WOC were understood. Low levels of water oxidation were detected in presence of a sacrificial electron acceptor.The gained understanding of the CT dynamics and recombination processes thus allows new strategies to improve the efficiency in molecular systems for solar energy conversion.
|
|
| 23. |
- Karnahl, Michael, et al.
(författare)
-
Synthesis and photophysics of a novel photocatalyst for hydrogen production based on a tetrapyridoacridine bridging ligand
- 2012
-
Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 393:1, s. 65-73
-
Tidskriftsartikel (refereegranskat)abstract
- Molecular photocatalysts allow for selectively tuning their function on a molecular level based on an in-depth understanding of their chemical and photophysical properties. This contribution reports the synthesis and photophysical characterization of the novel molecular photocatalyst [(tbbpy)(2)Ru(tpac)PdCl(2)](2+) RutpacPd (with tpac = tetrapyrido[3,2-a:2',3'-c:3 '',2 ''-h:2''',3'''-j]acridine) and its mononuclear building block. Furthermore, detailed photocatalytic activity measurements of RutpacPd are presented. The introduction of the tpac-ligand into the molecular framework offers a potential route to reduce the impact of water as compared to the well-studied class of RutpphzPd (with tpphz = tetrapyrido[3,2-a:2',3'-c:300,2 ''-h: 2''',3'''-j] phenazine) complexes. The distinct impact of water on the electron-transfer processes in tpphz-ligands stems from the possibility of water to form hydrogen bonds to the phenazine nitrogen atoms and will potentially reduced when replacing the phenazine by the acridine unit. The effect of this structural variation on the catalytic properties and the underlying ultrafast intramolecular charge transfer behavior will be discussed in detail.
|
|
| 24. |
- Karnahl, Michael, et al.
(författare)
-
Tuning of Photocatalytic Hydrogen Production and Photoinduced Intramolecular Electron Transfer Rates by Regioselective Bridging Ligand Substitution
- 2011
-
Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 12:11, s. 2101-2109
-
Tidskriftsartikel (refereegranskat)abstract
- Artificial photosynthesis based on supramolecular photocatalysts offers the unique possibility to study the molecular processes underlying catalytic conversion of photons into chemical fuels in great detail and to tune the properties of the photocatalyst by alterations of the molecular framework. Herein we focus on both possibilities in studying the photocatalytic reduction of protons by derivatives of the well-known photocatalyst [(tbbpy)(2)Ru(tpphz)PdCl(2)](PF(6))(2) [4,4'-di-tert-butyl-2,2'-bipyridine (tbbpy), tetrapyrido[3,2-a:2',3'-c:3 '',2 ''-h:2'", 3'"-j]phenazine (tpphz)]. We report on a modified photocatalyst where the crucial bridging ligand tpphz is substituted by bromine and investigate the effect of the structural variation on the catalytic properties of the complex and its ultrafast intramolecular charge transfer behavior. It is found that structural modification stabilizes the phenanthroline-centered metal-to-ligand charge-transfer state on the tpphz moiety, thereby reducing the electron transfer gradient across the entire electron-relaying bridging ligand and at the same time accelerating nanosecond ground-state recovery. The same structural modifications cause an overall reduction of the catalytic activity of the complex. Thus, the results highlight the potential of small structural variations in the molecular framework of supramolecular catalysts in understanding the photoinduced charge-transfer processes and optimizing their catalytic performance.
|
|
| 25. |
- Kuhnt, Christian, et al.
(författare)
-
The impact of bromine substitution on the photophysical properties of a homodinuclear Ru-tpphz-Ru complex
- 2011
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 516:1-3, s. 45-50
-
Tidskriftsartikel (refereegranskat)abstract
- Ruthenium-polypyridine complexes play an important role as photosensitizers in supramolecular photocatalysis. Using multiple Ru-centers within a single supramolecular catalyst might be a promising path for improving its efficiency. The connection of several chromophores may, however, lead to direct interaction amongst individual photoactive centers, which is at the core of the work at hand. The work focuses on the photophysics of [(tbbpy)(2)Ru(3,16-Br(2)-tpphz)Ru(tbbpy)(2)](PF(6))(4) (1, tpphz = tetrapyrido[3,2-a: 2',3'-c: 3 '',2 ''-h:2''',3'''-j] phenazine, tbbpy = 4,4'-di-tert.-butyl-2,2'-bipyridine) and aims at detailing the impact of the bromine substituents on bridging ligand photoinduced intramolecular charge-transfer dynamics. It is shown that the introduction of the bromine reduces the driving force for intra-ligand charge-transfer steps and impacts exciton-exciton annihilation at high pump intensities.
|
|
| 26. |
- Meyer, Tobias, et al.
(författare)
-
A compact microscope setup for multimodal nonlinear imaging in clinics and its application to disease diagnostics
- 2013
-
Ingår i: Analyst. - : Royal Society of Chemistry (RSC). - 1364-5528. ; 138:14, s. 4048-4057
-
Tidskriftsartikel (refereegranskat)abstract
- The past years have seen increasing interest in nonlinear optical microscopic imaging approaches for the investigation of diseases due to the method's unique capabilities of deep tissue penetration, 3D sectioning and molecular contrast. Its application in clinical routine diagnostics, however, is hampered by large and costly equipment requiring trained staff and regular maintenance, hence it has not yet matured to a reliable tool for application in clinics. In this contribution implementing a novel compact fiber laser system into a tailored designed laser scanning microscope results in a small footprint easy to use multimodal imaging platform enabling simultaneously highly efficient generation and acquisition of second harmonic generation (SHG), two-photon excited fluorescence (TPEF) as well as coherent anti-Stokes Raman scattering (CARS) signals with optimized CARS contrast for lipid imaging for label-free investigation of tissue samples. The instrument combining a laser source and a microscope features a unique combination of the highest NIR transmission and a fourfold enlarged field of view suited for investigating large tissue specimens. Despite its small size and turnkey operation rendering daily alignment dispensable the system provides the highest flexibility, an imaging speed of 1 megapixel per second and diffraction limited spatial resolution. This is illustrated by imaging samples of squamous cell carcinoma of the head and neck (HNSCC) and an animal model of atherosclerosis allowing for a complete characterization of the tissue composition and morphology, i.e. the tissue's morphochemistry. Highly valuable information for clinical diagnostics, e. g. monitoring the disease progression at the cellular level with molecular specificity, can be retrieved. Future combination with microscopic probes for in vivo imaging or even implementation in endoscopes will allow for in vivo grading of HNSCC and characterization of plaque deposits towards the detection of high risk plaques.
|
|
| 27. |
- Meyer, Tobias, et al.
(författare)
-
Expanding Multimodal Microscopy by High Spectral Resolution Coherent Anti-Stokes Raman Scattering Imaging for Clinical Disease Diagnostics
- 2013
-
Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 1520-6882 .- 0003-2700. ; 85:14, s. 6703-6715
-
Tidskriftsartikel (refereegranskat)abstract
- Over the past years fast label-free nonlinear imaging modalities providing molecular contrast of endogenous disease markers with subcellular spatial resolution have been emerged. However, applications of these imaging modalities in clinical settings are still at the very beginning. This is because single nonlinear imaging modalities such as second-harmonic generation (SHG) and two-photon excited fluorescence (TPEF) have only limited value for diagnosing diseases due to the small number of endogenous markers. Coherent anti-Stokes Raman scattering (CARS) microscopy on the other hand can potentially be added to SHG and TPEF to visualize a much broader range of marker molecules. However, CARS requires a second synchronized laser source and the detection of a certain wavenumber range of the vibrational spectrum to differentiate multiple molecules, which results in increased experimental complexity and often inefficient excitation of SHG and TPEF signals. Here we report the application of a novel near-infrared (NIR) fiber laser of 1 MHz repetition rate, 65 ps pulse duration, and 1 cm(-1) spectral resolution to realize an efficient but experimentally simple SGH/TPEF/multiplex CARS multimodal imaging approach for a label-free characterization of composition of complex tissue samples. This is demonstrated for arterial tissue specimens demonstrating differentiation of elastic fibers, triglycerides, collagen, myelin, cellular cytoplasm, and lipid droplets by analyzing the CARS spectra within the C-H stretching region only. A novel image analysis approach for multispectral CARS data based on colocalization allows correlating spectrally distinct pixels to morphologic structures. Transfer of this highly precise but compact and simple to use imaging approach into clinical settings is expected in the near future.
|
|
| 28. |
- Potts, Nathan T. Z., et al.
(författare)
-
Probing the dye-semiconductor interface in dye-sensitized NiO solar cells
- 2020
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 153:18
-
Tidskriftsartikel (refereegranskat)abstract
- The development of p-type dye-sensitized solar cells (p-DSSCs) offers an opportunity to assemble tandem photoelectrochemical solar cells with higher efficiencies than TiO2-based photoanodes, pioneered by O'Regan and Gratzel [Nature 353, 737-740 (1991)]. This paper describes an investigation into the behavior at the interfaces in p-DSSCs, using a series of BODIPY dyes, BOD1-3. The three dyes have different structural and electronic properties, which lead to different performances in p-DSSCs. We have applied photoelectron spectroscopy and transient absorption spectroscopy to rationalize these differences. The results show that the electronic orbitals of the dyes are appropriately aligned with the valence band of the NiO semiconductor to promote light-induced charge transfer, but charge-recombination is too fast for efficient dye regeneration by the electrolyte. We attribute this fast recombination, which limits the efficiency of the solar cells, to the electronic structure of the dye and the presence of Ni3+ recombination sites at the NiO surface.
|
|
| 29. |
- Siebert, Ronald, et al.
(författare)
-
Fluorescence quenching in Zn2+-bis-terpyridine coordination polymers: a single molecule study
- 2012
-
Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501 .- 0959-9428. ; 22:31, s. 16041-16050
-
Tidskriftsartikel (refereegranskat)abstract
- A Zn2+-bis-terpyridine coordination polymer is investigated by single-molecule fluorescence spectroscopy (SMS). The bis-terpyridine ligands of the coordination polymers bear conjugated chromophores connecting the terpyridine spheres of the ligands, which resemble structural features of MEH-PPV. To the best of our knowledge this paper presents the first systematic SMS study on Zn2+-bis-terpyridine coordination polymers. Upon incorporation of free chromophores into the polymer, the fluorescence quantum yield of individual chromophores appears to be reduced. The reason for the reduced emission per chromophore in a polymer is investigated by brightness studies on single isolated polymer molecules. Furthermore, the experiments reveal that the Zn2+-bis-terpyridine coordination polymer contains a significantly larger fraction of effective chromophores, compared to one of the most common conjugated polymers, e. g., MEH-PPV. This finding is attributed to the particularly rigid geometry of the system at hand, which was corroborated by polarization-dependent experiments. Time-resolved experiments identified two different types of intensity fluctuations: small amplitude intensity fluctuations might correlate with switching of individual chromophores by structural fluctuations, while large amplitude jumps switch off the emission of the entire molecule. Finally, experiments under different atmospheric conditions offer further insights into the molecular mechanism and the nature of the quenchers involved in the blinking.
|
|
| 30. |
- Tschierlei, Stefanie, et al.
(författare)
-
Photophysics of an Intramolecular Hydrogen-Evolving Ru-Pd Photocatalyst
- 2009
-
Ingår i: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 15:31, s. 7678-7688
-
Tidskriftsartikel (refereegranskat)abstract
- Photoinduced electron-transfer processes within a precatalyst for intramolecular hydrogen evolution [(tbbpy)(2)Ru(tpphz)PdCl2](2+) (RuPd; tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine, tpphz = tetrapyrido[3,2-a:2',3'c:3 '',2 '',-h:2"',3'''-j]phenazine) have been studied by resonance Raman and ultrafast time-resolved absorption spectroscopy. By comparing the photophysics of the [(tbbpy)(2)Ru(tpphz)](2+) subunit Ru with that of the supramolecular catalyst RuPd, the individual electron-transfer steps are assigned to kinetic components, and their dependence on solvent is discussed. The resonance Raman data reveal that the initial excitation of the molecular ensemble is spread over the terminal tbbpy and the tpphz ligands. The subsequent excited-state relaxation of both Ru and RuPd on the picosecond timescale involves formation of the phenazine-centered intraligand charge-transfer state, which in RuPd precedes formation of the Pd-reduced state. The photoreaction in the heterodinuclear supramolecular complex is completed on a subnanosecond timescale. Taken together, the data indicate that mechanistic investigations must focus on potential rate-determining steps other than electron transfer between the photoactive center and the Pd unit. Furthermore, structural variations should be directed towards increasing the directionality of electron transfer and the stability of the charge-separated states.
|
|
| 31. |
- Umrao, Sima, et al.
(författare)
-
A possible mechanism for the emergence of an additional band gap due to a Ti-O-C bond in the TiO2-graphene hybrid system for enhanced photodegradation of methylene blue under visible light
- 2014
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:104, s. 59890-59901
-
Tidskriftsartikel (refereegranskat)abstract
- Here we report the experimental and theoretical study of two TiO2-graphene oxide (TG) and TiO2-reduced graphene oxide (TR) composites synthesized by a facile and ecological route, for enhanced visible light (similar to 470 nm) photocatalytic degradation of Methylene Blue (MB) (99% efficiency), with high rate constant values (1800% over bare TiO2). TG couples TiO2 nanopowder with Graphene Oxide (GO) while TR couples it with reduced graphene oxide (RGO). The present study, unlike previous reports, discusses never-before-reported double absorption edges obtained for both TG (3.51 eV and 2.51 eV) and TR (3.42 eV and 2.39 eV) composites, which represents the reason behind feasible visible light (2.56 eV) induced photocatalysis. TiO2 domains in the composites dominate the higher band edge, while GO/RGO domains explain the lower band edge. Formation of Ti-O-C bonds in both TG and TR drives the shifting upwards of the valence band edge and reduction in band gap. Further, these bonds provide a conductive pathway for charge carriers from TiO2 nanopowder to the degraded species via the GO/RGO matrix, resulting in decreased charge carrier recombination in TiO2 and enhanced efficiency. To attest that the developed theory is correct, density function theory (DFT) calculations were performed. DFT obtained energetics and electronic structures support experimental findings by demonstrating the role of the Ti-O-C bond, which results in double band edge phenomenon in composites. Finally, the mechanism behind MB degradation is discussed comprehensively and the effect of the weight percent of GO/RGO in the composite on the rate constant and photodegradation efficiency has been studied experimentally and explained by developing analytical equations.
|
|
| 32. |
- Vlachopoulos, Nick, et al.
(författare)
-
New approaches in component design for dye-sensitized solar cells
- 2021
-
Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry. - 2398-4902. ; 5:2, s. 367-383
-
Tidskriftsartikel (refereegranskat)abstract
- The present perspective presents a number of issues related to the current direction of DSSC research, with emphasis on the transition from iodide-containing electrolyte to charge-transport media (CTMs), electrolytes or solid-state conductors based on inorganic coordination complexes, aiming to attain a better light-to-electricity conversion efficiency, associated with larger photovoltage, and long-term stability. Such a change necessitates the concomitant introduction of novel dyes and counter electrodes. The first part of the perspective introduces an overview of the DSSC field and a number of considerations related to the transition from the triiodide/iodide-based CTM to CTMs based on alternative systems. Subsequently, the recent developments of CTM based on Cu coordination complexes are discussed, from the inorganic physical chemistry point of view, including some highlights about novel dyes associated to these CTMs. Finally, several preparation methods and applications of different types of novel carbonaceous counter electrode substrates, related to the application of the aforementioned novel CTMs, are presented.
|
|
| 33. |
- Vogler, Nadine, et al.
(författare)
-
Multimodal imaging to study the morphochemistry of basal cell carcinoma
- 2010
-
Ingår i: Journal of Biophotonics. - : Wiley. - 1864-063X. ; 3:10-11, s. 728-736
-
Tidskriftsartikel (refereegranskat)abstract
- Basal cell carcinoma is the most abundant malignant neoplasm in humans, the pathology of which is characterized by an abnormal proliferation of basal cells. Basal cell carcinoma can show a variety of different morphologies, which are based on different cellular biology. Furthermore, the carcinoma often grows invisibly to the eye imbedded in the surrounding skin. Therefore, in some cases its clinical detection is challenging. Thus, our work aims at establishing an unsupervised tissue classification method based on multimodal imaging and the application of chemometrics to discriminate basal cell carcinoma from non-diseased tissue. A case study applying multimodal imaging to ex-vivo sections of basal cell carcinoma is presented. In doing so, we apply a combination of various linear and non-linear imaging modalities, i.e. fluorescence, Raman and second-harmonic generation microscopy, to study the morphochemistry of basal cell carcinoma. The joint information content obtained by such multimodal approach in studying various aspects of the malignant tissue alterations associated with basal cell carcinoma is discussed. [GRAPHICS] Multimodal imaging combining coherent anti-Stokes Raman scattering, second-harmonic generation and two-photo fluorescence is combined with Raman spectroscopy to investigate the morphochemistry of human basal cell carcinoma.
|
|
| 34. |
- Wood, Christopher J., et al.
(författare)
-
A comprehensive comparison of dye-sensitized NiO photocathodes for solar energy conversion
- 2016
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 18:16, s. 10727-10738
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated a range of different mesoporous NiO electrodes prepared by different research groups and private firms in Europe to determine the parameters which influence good quality photoelectrochemical devices. This benchmarking study aims to solve some of the discrepancies in the literature regarding the performance of p-DSCs due to differences in the quality of the device fabrication. The information obtained will lay the foundation for future photocatalytic systems based on sensitized NiO so that new dyes and catalysts can be tested with a standardized material. The textural and electrochemical properties of the semiconducting material are key to the performance of photocathodes. We found that both commercial and non-commercial NiO gave promising solar cell and water-splitting devices. The NiO samples which had the two highest solar cell efficiency (0.145% and 0.089%) also gave the best overall theoretical H-2 conversion.
|
|
