Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Spectroscopy and photophysics of self-organized zinc porphyrin nanolayers. 2. Transport properties of singlet excitation
    Donker, H. ; Hoek, A. van; Schaik, W. ; Koehorst, R.B.M. ; Yatskou, M.M. ; Schaafsma, T.J. - \ 2005
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 109 (2005)36. - ISSN 1520-6106 - p. 17038 - 17046.
    monte-carlo simulation - energy-transfer - impurity scattering - molecular-crystals - exciton transport - films - fluorescence - systems - phthalocyanine - luminescence
    Exciton diffusion has been studied in 5-25-nm-thick films of zinc tetra-(p-octylphenyl)-porphyrin (ZnTOPP) spin-coated onto quartz slides by intentional doping with quenchers using steady-state as well as time-resolved fluorescence spectroscopy. The fluorescence spectra of the films are very similar to those of solutions, indicating emission from localized exciton states. From the dependence of the fluorescence quenching on the quencher concentration and fluorescence lifetime measurements, the exciton diffusion can be concluded to be quasi-one-dimensional with an exciton diffusion length of 9 ± 3 nm and an intrastack energy-transfer rate constant of 1011-1012 s-1. From fluorescence anisotropy decay measurements, we conclude that neighboring stacks aggregate in a herringbone structure, forming ordered domains that are randomly oriented in the substrate plane. These measurements indicate an interstack energy-transfer rate constant of (7 ± 2) × 1010 s-1
    Spectroscopy and photophysics of self-organized zinc porphyrin nanolayers. 3. Fluorescence detected magnetic resonance of triplet states
    Schaafsma, T.J. ; Dag, I. ; Sitters, R. ; Glasbeek, M. ; Lifshitz, E. - \ 2005
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 109 (2005)36. - ISSN 1520-6106 - p. 17047 - 17054.
    columnar liquid-crystals - octasubstituted phthalocyanine derivatives - mesomorphic phase-transitions - electron-spin-resonance - optical-detection - solar-cells - films - odmr - tetraphenylporphyrins - photoluminescence
    Fluorescence detected magnetic resonance (FDMR) has been applied to ~25-nm-thick porphyrin films, containing ordered domains of zinc tetra-(p-octylphenyl)-porphyrin (ZnTOPP) spin-coated onto quartz slides. Illuminating the films at 1.4 K with 457.9-nm light from a continuous wave Ar+ laser produces at least two different, Jahn-Teller-distorted, ZnTOPP triplet species, labeled i and ii. Microwave-induced magnetic resonance of i and ii in the absence or presence of an externally applied magnetic field affects the fluorescence intensity of ZnTOPP, thus allowing FDMR. For triplet species i, formed in films spin-coated from toluene solution, the zero-field splitting (ZFS) parameters were determined as D = (316.9 ± 0.1) × 10-4 cm-1 and E = (32.0 ± 0.5) × 10-4 cm-1. By exposure of the spin-coated films to chloroform vapor at room temperature, triplet i is converted into species ii, with D = (295 ± 3) × 10-4 cm-1 and E = (121 ± 3) × 10-4 cm-1. For the excited triplet state of ZnTOPP in a toluene glass, ZFS parameters with values of D = (295 ± 1) × 10-4 cm-1 and E = (91 ± 1) × 10-4 cm-1 are found. From a combined study of the FDMR- and microwave-induced fluorescence spectra, i and ii are identified as unligated and ligated ZnTOPP triplet species, respectively. From the asymmetrically shaped zero-field FDMR signals of i, we conclude that the local crystal field perturbations of the stacked molecules are anisotropic. The FDMR results of the ZnTOPP films are compared with those for a film of zinc tetraphenylporphyrin (ZnTPP), which lacks the octyl substituents, and therefore is nonordered. Upon illumination, the ZnTPP films contain only a single, ligated, triplet species with ZFS parameters very similar to those of ligated ZnTOPP. At ~5 K, the lifetime of triplet i is considerably shortened compared to that of ZnTOPP in a glass at the same temperature
    Spectroscopy and photophysics of self-organized zinc porphyrin nanolayers. 1. Optical spectroscopy of excitonic interactions involving the soret band
    Donker, H. ; Koehorst, R.B.M. ; Schaafsma, T.J. - \ 2005
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 109 (2005)36. - ISSN 1520-6106 - p. 17031 - 17037.
    columnar liquid-crystals - monte-carlo simulation - alkoxy units - solar-cells - films - tetraphenylporphyrins - fluorescence - phthalocyanines - aggregation - orientation
    The photophysical properties of excited singlet states of zinc tetra-(p-octylphenyl)-porphyrin in 5-25-nm-thick films spin-coated onto quartz slides have been investigated by optical spectroscopy. Analysis of the polarized absorption spectra using a dipole-dipole exciton model with two mutually perpendicular transition dipole moments per molecule shows that the films are built from linear aggregates, i.e., stacks with a slipped-deck-of-cards configuration. The molecular planes of the porphyrins in the stacks are found to be perpendicularly oriented with respect to the substrate plane. Assuming a value of 2-3 for the dielectric constant of the film, from the excitonic shift, an angle of 44 ± 3 and an interplanar distance of 0.35-0.36 nm between adjacent porphyrins are calculated, close to the ground-state geometry in solution. The ordering in these films was further investigated by the effects of various solvents and temperature annealing. Spin-coating from toluene as a solvent results in highly ordered films, and annealing of these films has little effect on their absorption spectra. However, spin-coating from chloroform or pyridine or exposure of the films to these solvents in their vapor phases changes their ordering presumably due to incorporation of residual solvent molecules. Annealing yields absorption spectra identical to those of films spin-coated from toluene. The absorption spectra are insensitive to atmospheric moisture, in contrast to those of zinc tetraphenylporphyrin films lacking octyl substituents
    Electronic spectra and fluorescence polarization kinetics of thin Zn-porphyrin films
    Yatskou, M.M. ; Apanosovich, V.V. ; Koehorst, R.B.M. ; Hoek, A. van; Schaafsma, T.J. - \ 2003
    Journal of Applied Spectroscopy 70 (2003)3. - ISSN 0021-9037 - p. 372 - 377.
    The photophysical properties of thin films of Zn-monopyridyltriphenylporphyrin (Zn(4-Py)TrPP) obtained by the method of centrifugation on a quartz film substrate have been investigated. The results of the analysis of the measured excitation and luminescence spectra and also of the kinetic curves of fluorescence depolarization, as they decay, of the Zn(4-Py)TrPP films permit the conclusion that Zn-meso-monopyridylporphyrins self-organize into aggregates. The symmetric closed tetramer ([Zn(4-Py)TrPP]4) seems to be the most probable aggregate of Zn-meso-monopyridylporphyrins.
    Zuinigheid met vlijt
    Schaafsma, T.J. - \ 2002
    Wageningen : Wageningen Universiteit - 38
    natuurlijke hulpbronnen - energiebehoud - energiebronnen - duurzaamheid (sustainability) - natural resources - energy conservation - energy sources - sustainability
    Photonic antenna system for light harvesting, transport and trapping
    Calzaferri, G. ; Pauchard, M. ; Maas, H. ; Huber, S. ; Khatyr, A. ; Schaafsma, T.J. - \ 2002
    Journal of Materials Chemistry 12 (2002)1. - ISSN 0959-9428 - p. 1 - 13.
    loaded zeolite-l - wide-bandgap semiconductors - solar-cells - dye molecules - spectral sensitization - artificial antenna - energy migration - metal-complexes - emitting-diodes - films
    Host¿guest composites with photonic antenna properties are described. The material consists of cylindrical zeolite L crystals the channels of which are filled with chains of joined but electronically non-interacting dye molecules. Light shining on a crystal is first absorbed and the energy is then transported by the dye molecules inside the tubes to the desired part. Data on crystals in the size range of 30 nm up to 3000 nm are reported. The synthesis principle we are using is based on the fact that molecules can diffuse into individual channels. This means that given the appropriate conditions, they can also leave the zeolite by the same way. In some cases, however, it is desirable to block their way out, for stability reasons. This is done by adding a closure molecule. The general approach to connect the antenna function to its surroundings is to add stopcock molecules which generally consist of a head, a spacer and a label. They can either trap excitation energy on the external surface or inject excitation energy into the dye-loaded crystal. The stopcock molecules act as bridges between the dye molecules inside the channels and the outside world. Functionalisation of the closure and the stopcock molecules is an option for tuning e.g. wettability, refractive index, and chemical reactivity. The wide-ranging tunability of the dye¿zeolite L composites makes them useful for many applications. We discuss demonstration experiments which show the process of energy transfer and energy migration as educational tools, applications as high quality and non-toxic pigments, use as strongly luminescent pigments applicable as colour-changing media for LEDs, options for realising nanoscaled laser materials, and finally the challenge for realising solid state solar cells based on sensitisation of a thin semiconductor layer by energy transfer, the reversal of which can also lead to a new generation of LEDs
    Spectroscopic properties of a self-assembled zinc porphyrin tetramer I. Steady state optical spectroscopy
    Yatskou, M.M. ; Koehorst, R.B.M. ; Donker, H. ; Schaafsma, T.J. - \ 2001
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 105 (2001)51. - ISSN 1089-5639 - p. 11425 - 11431.
    Aggregation of zinc mono-(4-pyridyl)-triphenylporphyrin (ZnPyP) in toluene and polystyrene/toluene mixtures has been investigated by steady-state optical spectroscopy. The Q-band absorption spectra, as well as the fluorescence spectra, show a temperature-dependent red shift as a result of ligation of the porphyrin zinc center. The smallest aggregate that can account for the optical spectra and their concentration dependence is a symmetrical tetramer in which each zinc atom is ligated to a pyridyl substituent of a neighboring porphyrin molecule. The Soret band shows a splitting, which can be explained by applying simple exciton theory to the tetramer. The equilibrium constant and thermodynamic parameters for the monomer-tetramer equilibrium have been determined as K = (6.2 ± 0.8) x 1013 M-3, H = -40 ± 2 kCalM-1, S = -150 ± 10 CalK-1M-1, in agreement with tetramer formation.
    Spectroscopic properties of a self-assembled zinc porphyrin tetramer II. Time-resolved fluorescence spectroscopy
    Yatskou, M.M. ; Koehorst, R.B.M. ; Hoek, A. van; Donker, H. ; Schaafsma, T.J. - \ 2001
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 105 (2001)51. - ISSN 1089-5639 - p. 11432 - 11440.
    Excited-state kinetics of complexes of a functionalized zinc tetraphenylporphyrin (ZnTPP) derivative, zinc mono(4-pyridyl)triphenylporphyrin (ZnPyP) in toluene and polystyrene/toluene mixtures have been investigated by time-resolved fluorescence spectroscopy. In addition to the ~2.0 ns monomer fluorescence lifetime, a 1.5 ns component was found by applying global analysis to the time-resolved fluorescence decay. The 1.5 ns component is assigned to a cyclic porphyrin tetramer [Part I], with a 1 ns rotational correlation time at 10 C. The initial fluorescence anisotropy of the monomer is found to be 0.1. In the tetramer an additional depolarization process occurs with a correlation time of ~31 ps, resulting in a further decrease of the anisotropy from 0.1 to 0.025. This additional depolarization is ascribed to singlet energy transfer between the porphyrin units that constitute the tetramer. The intramolecular energy transfer processes have been simulated using the Monte Carlo method, yielding rate constants of (26 ± 4 ps)-1 and (180 ps)-1 for energy transfer between nearest neighbor and next nearest neighbor porphyrins in the tetramer.
    Spectroscopic study of erythrosin B in PVA films
    Stomphorst, R.G. ; Zwan, G. van der; Zandvoort, M.A.M.J. van; Sieval, A.B. ; Zuilhof, H. ; Vergeldt, F.J. ; Schaafsma, T.J. - \ 2001
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 105 (2001). - ISSN 1089-5639 - p. 4235 - 4240.
    The effects of increasing concentration (10-7-2.5 x 10-3 mol/g) of Erythrosin B (Ery B) in poly(vinyl alcohol) films on its visible absorption spectrum have been investigated. In a concentration range of 2 x 10-7-10-5 mol/g, no effects on the absorption spectrum are found. By contrast, within this concentration range, time-resolved fluorescence experiments (fluorescence and anisotropy decay) reveal the presence of energy transfer between Ery B molecules, followed by fluorescence at low concentrations and fluorescence quenching at higher concentrations. At a concentration of 5 x 10-5 mol/g, the absorption spectrum broadens as compared to the monomeric spectrum and fluorescence is almost completely quenched. A further increase of the concentration results in a blue shift of the absorption spectrum. Using molecular mechanics calculations, it is shown that the initial broadening can be ascribed to excitonic interactions between randomly oriented molecules, whereas the blue shift at higher concentrations can be explained by the formation of oligomeric structures. At concentrations of 2.5 x 10-3 mol/g, the molecules are closely packed, resulting in a contribution at the red edge of the absorption spectrum.
    Quantitative NMR microscopy of osmotic stress responses in maize and pearl millet
    Weerd, L. van der; Claessens, M.A.E. ; Ruttink, T. ; Vergeldt, F.J. ; Schaafsma, T.J. ; As, H. van - \ 2001
    Journal of Experimental Botany 52 (2001). - ISSN 0022-0957 - p. 2333 - 2343.
    Spectral effects of excitonic interactions in disordered solid films
    Stomphorst, R.G. ; Schaafsma, T.J. ; Zwan, G. van der - \ 2001
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 105 (2001)17. - ISSN 1089-5639 - p. 4226 - 4234.
    This paper describes the absorbance properties of pigments in disordered films. The fluorescence quenching of pigment systems at low concentrations are usually attributed to the presence of so-called statistical pairs. We show that, if line broadening mechanisms are taken into account such as homogeneous and inhomogeneous broadening and statistical distribution of distances between the pigments, the number of potential quenchers decreases dramatically, because all of these effects lead to an increase of the dipole strength of the lowest excitonic state of a dimer. We also show, on the basis of Monte Carlo calculations on assemblies of pigments, that spectral effects beyond a general broadening of the spectrum will not be observed, even for concentrated systems, where a larger number of these statistical pairs may assumed to be present.
    Photophysical and structural properties of saddle-shaped free base porphyrins: Evidence for an "orthogonal" dipole moment
    Sazanovich, I.V. ; Galievski, V.A. ; Hoek, A. ; Schaafsma, T.J. ; Malinovski, V.L. ; Holten, D. ; Chirvony, V.S. - \ 2001
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 105 (2001)32. - ISSN 1520-6106 - p. 7818 - 7829.
    A study of energy transfer processes in zinc-porphyrin films using Monte Carlo simulation of fluorescence decay
    Yatskou, M.M. ; Donker, H. ; Koehorst, R.B.M. ; Hoek, A. van; Schaafsma, T.J. - \ 2001
    Chemical Physics Letters 345 (2001)1-2. - ISSN 0009-2614 - p. 141 - 150.
    Nonisotropic excitation energy transport in organized molecular systems: Monte Carlo simulation-based analysis of fluorescence and fluorescence anisotropy decay
    Yatskou, M.M. ; Donker, H. ; Novikov, E.G. ; Koehorst, R.B.M. ; Hoek, A. van; Apanasovich, V.V. ; Schaafsma, T.J. - \ 2001
    The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 105 (2001)41. - ISSN 1089-5639 - p. 9498 - 9508.
    Spectral Sensitization of TiO2 Substrates by Monolayers of Porphyrin Heterodimers
    Koehorst, R.B.M. ; Boschloo, G.K. ; Savenije, T.J. ; Goossens, A. ; Schaafsma, T.J. - \ 2000
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 104 (2000)10. - ISSN 1520-6106 - p. 2371 - 2377.
    Photoelectrochemical cells have been constructed by depositing monolayers of oriented covalently linked zinc/free base porphyrin heterodimers onto ~30 nm nonporous layers of TiO2 on ITO, deposited by metal-organic chemical vapor deposition (MO-CVD), and onto ~100 nm porous, nanostructured TiO2 layers, spin-coated from a suspension of P25 (Degussa) on ITO. Fluorescence quenching of the dyes on both types of TiO2 substrates is compared with that of dilute solutions of the dyes and with that of dye-coated, porous ZrO2 (Degussa) substrates. By functionalizing one of the porphyrin dimer components with carboxylic substituents, which bind to the TiO2 or ZrO2 substrate surface, either the zinc porphyrin (ZnP) or the free base porphyrin (H2P) component of the dimer can be made to be in direct contact with the substrate. These dimer-substrate arrangements are denoted ZnP-H2P- -TiO2 (dimer 1) and H2P-ZnP- -TiO2 (dimer 2), respectively, where "- -" denotes binding of the carboxyl-substituted porphyrin in the heterodimer to the substrate surface. In solution as well as deposited on ZrO2, in contact with the solvent without a redox couple, both types of dimers show efficient internal ZnP to H2P energy transfer. Deposited on TiO2, in the presence of the solvent, monolayers of both types of dimers show less efficient energy transfer than the dimers on ZrO2. For a ZnP-H2P- -TiO2 electrochemical cell the photocurrent action spectrum reproduces the absorption spectrum, i.e., contains contributions of both the ZnP and H2P moieties. By contrast, for H2P-ZnP- -TiO2 cells mainly the ZnP dimer component contributes to the photocurrent, demonstrating that in H2P-ZnP- -TiO2 cells electron transfer from the ZnP into the TiO2 substrate is faster than energy transfer to the adjacent free base porphyrin. The photocurrent action spectrum of the ZnP-H2P- -TiO2 cell also demonstrates that energy transfer in monolayers of this dimer results in sensitization of the semiconductor substrate, since the spectral response of a cell is enhanced with respect to that of a cell with a monolayer of a monomeric sensitizer. These results are relevant for the construction of a solar cell containing a supramolecular, light-collecting antenna
    Comparative study of the photophysical properties of nonplanar tetraphenylporphyrin and octaethylporphyrin diacids
    Chirvony, V.S. ; Hoek, A. van; Galievsky, V.A. ; Sazanovich, I.V. ; Schaafsma, T.J. ; Holten, D. - \ 2000
    The Journal of Physical Chemistry Part B: Condensed Matter, Materials, Surfaces, Interfaces & Biophysical 104 (2000). - ISSN 1520-6106 - p. 9909 - 9917.
    The photophysical properties of the lowest excited singlet states, S1(,*), of two porphyrin diacids have been investigated. The diacids are H4TPP2 and H4OEP2 , the diprotonated forms of free base tetraphenylporphyrin (H2TPP) and octaethylporphyrin (H2OEP), respectively. Both diacids exhibit perturbed static and dynamic characteristics relative to the parent neutral complexes in solution at room temperature. These properties include enhanced yields of S1 S0 radiationless deactivation (internal conversion), which increase from ~0.1 for H2TPP and H2OEP to 0.4 for H4OEP2 and 0.6 for H4TPP2 . The fluorescence lifetimes of both diacids are strongly temperature dependent, with an activation enthalpy of ~1400 cm-1 for S1-state deactivation. The enhanced nonradiative decays and many other photophysical consequences of diacid formation are attributed primarily to nonplanar macrocycle distortions. Both H4TPP2 and H4OEP2 have been shown previously by X-ray crystallography to adopt saddle-shaped conformations, and the magnitudes of the perturbed properties for the two diacids in solution correlate with the extent of the deviations from planarity in the crystals. A model is proposed to explain the nonradiative decay behavior of the porphyrin diacids that is relevant to nonplanar porphyrins in general. The model includes the existence of decay funnels on the S1(,*)-state energy surface that are separated from the equilibrium conformation and other minima by activation barriers. It is suggested that these funnels involve configurations at which the potential-energy surfaces of the ground and excited states approach more closely than at the equilibrium excited-state structure(s) from which steady-state fluorescence occurs. Possible contributions to the relevant nuclear coordinates are discussed.
    Optical spectroscopy and simulation-based analysis of thin films of zinc porphyrin derivatives
    Yatskou, M.M. ; Schaafsma, T.J. ; Apanasovich, V.V. ; Koehorst, R.B.M. ; Hoek, A. van; Novikov, E.G. - \ 1999
    In: Spectroscopy of Biological Molecules: New Directions / Greve, J., Puppels, G.J., Otto, C., Dordrecht : Kluwer Academic Publishers - p. 179 - 180.
    Visible Light Sensitization of Titanium Dioxide with Self-Organized Porphyrins : Organic P-I-N Solar Cells
    Wienke, J. ; Schaafsma, T.J. ; Goossens, A. - \ 1999
    Journal of Chemical Physics 103 (1999)14. - ISSN 0021-9606 - p. 2702 - 2708.
    Free base 5,10,15,20-tetrakis(4-n-octylphenyl) porphyrin (H2TOPP) belongs to a class of self-organizing porphyrins. Since its LUMO lies above the conduction band of titanium dioxide (TiO2) and its visible light absorption is very strong, sensitization of TiO2 with H2TOPP thin films is possible. After spin-coating this porphyrin onto n-type TiO2, the Fermi-level of H2TOPP is measured, from which it is established that it behaves as intrinsic semiconductor, i.e., donor and acceptor densities, if present, compensate each other. Thin films of zinc 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin (ZnTCPP) are also investigated and show profound p-type character. Moreover, the LUMO of ZnTCPP is located about 0.4 eV above that of H2TOPP making an organic based heterostructure p-i-n solar cell possible. In this cell, H2TOPP is sandwiched between n-type TiO2 and p-type ZnTCPP. The LUMO positions of these porphyrins is such that unidirectional energy transfer from ZnTCPP to H2TOPP occurs. By carefully comparing the photocurrent action spectra with the absorption spectra, it could be established that a built-in field in the p-i-n structure is beneficial for solar-energy conversion.
    Excitonic Interactions in Covalently linked Porphyrin Dimers with Rotational Freedom
    Stomphorst, R.G. ; Koehorst, R.B.M. ; Zwan, G. van de; Benthem, L. ; Schaafsma, T.J. - \ 1999
    Journal of Porphyrins and Phthalocyanines 3 (1999). - ISSN 1088-4246 - p. 346 - 354.
    Studying the structures of Zinc-porphyrins by the methods of the fluorescence spectroscopy
    Apanasovich, V.V. ; Novikov, E.G. ; Yatskou, M.M. ; Koehorst, R.B.M. ; Schaafsma, T.J. ; Hoek, A. van - \ 1999
    Journal of Applied Spectroscopy 66 (1999)4. - ISSN 0021-9037 - p. 613 - 616.
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