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ABSTRACT: A synthetic route to symmetrical tetraaryltetraanthra[2,3]porphyrins (Ar4TAP) was developed. Ar4TAP bearing various substituents in meso-phenyls and anthracene residues were prepared from the corresponding pyrrolic precursors. The synthesized porphyrins possess high solubility and exhibit remarkably strong absorption bands in the near-infrared region (790-950 nm). The scope of the method, selection of the peripheral substituents, choice of the metal and their influence on the optical properties are discussed together with the first X-ray crystallographic data for anthraporphyrin.
The Journal of Organic Chemistry 12/2012; · 4.45 Impact Factor
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ABSTRACT: The synergetic effect on the efficiency of triplet-triplet-annihilation-assisted photon upconversion, as a result of a synthetic procedure for simultaneous and independent optimization of the intrinsic efficiencies of triplet-triplet transfer and triplet-triplet annihilation, is demonstrated. The new system shows high upconversion quantum yields of order of 0.11.
ChemPhysChem 06/2012; 13(13):3112-5. · 3.41 Impact Factor
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ABSTRACT: In this paper, we demonstrate energetically conjoined triplet–triplet annihilation-assisted photon energy upconversion (UC) operating in an aqueous environment. Obtained micellar structures show very efficient UC emission in a water environment under extremely low excitation light intensity, down to 10 mW cm−2. The demonstrated sub-linear intensity dependence of the UC emission is of crucial importance for life science applications, allowing upconverted photons to be generated even at low intensity that then serve as a local, in situ, optical excitation source for subsequent light-triggered processes.
New Journal of Physics 08/2011; 13(8):083035. · 4.18 Impact Factor
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ABSTRACT: The mechanism of triplet–triplet annihilation (TTA)-induced up-converted (UC) delayed luminescence is studied in two different binary organic systems consisting of platinum(II) octaethyl porphyrin (PtOEP) mixed with either poly(fluorene) (PF26) or ladder-type pentaphenylene (L5Ph). Cyclic voltammetry and differential pulse voltammetry are employed for estimating the ionization potentials of PtOEP and L5Ph. Delayed luminescence spectroscopy sets the energy of the lowest excited triplet state of L5Ph 0.20 eV higher than the triplet state of PtOEP (1.90 eV). The different phosphorescence PtOEP lifetime indicates differences in PtOEP aggregation in the polymer matrices. The presented results propose that the difference in the relative intensities of the delayed UC luminescence is determined by the difference between the ionization potentials of PtOEP and the polymer matrix. In the solid state, the electric-field-induced quenching of the delayed L5Ph UC luminescence suggests the formation of an intermediate charge-transfer state after the TTA within the PtOEP domains.Keywords: triplet−triplet annihilation; delayed fluorescence; up-conversion; organic photovoltaics; electron-exchange energy transfer; charge transfer
07/2011;
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ABSTRACT: The photophysical properties of a π-conjugated polymer containing 2,2'-bipyridyl alternated with 2,5-dihexyloxyphenylene units (PBPyDHP) are investigated experimentally in terms of the conditions used (solvent, concentration, presence or absence of molecular oxygen, and optical excitation power). The experimental results have suggested that the fluorescence from PBPyDHP can be tuned by proper selection of the experimental conditions showing only one or two emission peaks: 445 nm (blue) and 555 nm (green). The observed effects were interpreted in terms of the twisted intramolecular charge transfer (TICT) theory. This is the first experimental report showing the interconversion of an usual fluorescence, called locally emission state (LE), to a TICT state in second scale time by varying the excitation power; that is, even though the torsion of only one fluorophore occurs in a nano or picosecond scale, the global change (the interconversion for all fluorophores) has occurred in the second time scale.
The Journal of Physical Chemistry B 05/2011; 115(20):6385-94. · 3.70 Impact Factor
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ABSTRACT: The first energetically conjoined TTA-assisted photon energy upconversion operating in cell tissue is described. The synthesized nanocapsules with the encapsulated UC dye system consisting of an emitter and a sensitizer show very efficient UC emission in aqueous dispersion under extremely low excitation intensity down to 0.05 W · cm(-2) so that tissue and cells are not affected by the excitation light. The demonstrated sub-linear intensity dependence of the UC emission is of crucial importance for life-science applications as the UC photon could serve as a local or in situ optical excitation source for subsequent light-triggered processes.
Macromolecular Bioscience 03/2011; 11(6):772-8. · 3.89 Impact Factor
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ABSTRACT: Oxygen permeabilities of nanocomposite films consisting of poly(methyl methacrylate) (PMMA) and different amounts of spherical zinc oxide (ZnO) nanoparticles were determined to investigate the barrier effect of this material with respect to particle content. A method was applied which is based on quenching of an excited phosphorescent dye by oxygen. Possible effects of the nanoparticles on the response of the dye molecules were investigated and were ruled out.
Macromolecular Rapid Communications 02/2009; 30(4-5):394-401. · 4.60 Impact Factor
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Chemistry 11/2008; 14(32):9846-50. · 5.93 Impact Factor
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ABSTRACT: In this paper, we demonstrate the first all-organic, transparent, flexible, versatile colour displays based upon triplet–triplet annihilation assisted photon energy upconversion in viscous polymeric matrix. The devices work with ultra-low excitation intensities down to 20 mW cm−2 red or near-IR light. The displays are based on metallated-porphyrin sensitizers in combination with emitters dispersed in a transparent polymeric matrix and are driven by galvo-scanned laser diodes. The displays have external quantum yield as high as 3.2%. The response time can be adjusted to specific application requirements—up to 80 μs allowing kHz-refreshment rate of the displayed information. It is possible to easily tune the optical density of the screens in order to obtain a desired transmittance for the excitation beam. We demonstrate the ability to achieve multicolour emission, using only one excitation source. There are practically no display size limitations.
New Journal of Physics 10/2008; 10(10):103002. · 4.18 Impact Factor
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ABSTRACT: Chain length dependence of the photoemission (fluorescence, phosphorescence, delayed fluorescence) and the respective life times of poly conjugated macromolecules is subject of controversy since long. An underlying question concerns coherence and extension/localization of the photoexcited states. Energy transfer within and between macromolecules as well as between sensitizers and macromolecules are relevant processes in systems to be used for displays or solar energy harvesting. In this context our recent work on photophysical characterization of pure oligo(fluorene)s and of the same oligomers containing just one fluorenone (“keto-defect”) group is reviewed. Energy transfer between poly(fluorene)s and metal porphyrins is also covered. Triplet- triplet-annihilation opens a route to efficient non-coherent energy upconversion at ultralow excitation intensity (ca 1 Wcm−2). Light from the red region (635–700 nm) of terrestrial sun-light is converted into the green region with ΔE ≥ 0.5 eV.
Macromolecular Symposia 07/2008; 268(1):1 - 8.
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Macromolecular Chemistry and Physics 09/2007; 208(19‐20):2173 - 2188. · 2.36 Impact Factor
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Stanislav Baluschev,
Vladimir Yakutkin,
Tzenka Miteva,
Yuri Avlasevich,
Sergei Chernov,
Sergei Aleshchenkov,
Gabriele Nelles,
Andrei Cheprakov,
Akio Yasuda,
Klaus Müllen,
Gerhard Wegner
Angewandte Chemie International Edition 02/2007; 46(40):7693-6. · 13.45 Impact Factor
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ABSTRACT: Spectroscopic and morphological studies on a series of rod-coil block copolymers containing terfluorene segments as the rigid blocks and polystyrene as the flexible parts demonstrate an increase in the photoluminescence intensity and the exciton lifetime as well as formation of isolated spheres as thin films upon thermal annealing in air (200 degrees C for 30 min). Moreover, no appearance of the low energy emission band centered at 520 nm was found after the same thermal treatment which permits these copolymers to emit pure blue light.
The Journal of Physical Chemistry B 04/2006; 110(10):4657-62. · 3.70 Impact Factor
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ABSTRACT: Up-conversion phenomena are traditionally related to two- or multiphoton processes occurring under relatively high excitation intensities. Here we present the first results of ultralow excitation intensity (in order of Wcm(-2)) continuous-wave (CW) excited up-conversion fluorescence in Kretschmann surface plasmon geometry. The active system is a blue-emitting polymer matrix blended with metalated porphyrine macrocycles. The up-conversion fluorescence is a consequence of a two-particle triplet-triplet annihilation process (TTA).
Nano Letters 01/2006; 5(12):2482-4. · 13.20 Impact Factor
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ABSTRACT: We report on amplification of blue light (469 nm) via amplified spontaneous emission in asymmetric planar waveguides of a fully arylated polyindenofluorene derivative. A very low threshold value of about 3 μJ/cm2 ( ∼ 375 W/cm2) for amplification of light has been demonstrated by pumping the waveguides at 3.0 eV (410 nm) with a stripe shape excitation beam. Moderate gain coefficients up to 21 cm−1 and loss coefficients around 6 cm−1 have been measured. All measurements were performed under ambient conditions. No sample degradation could be observed which testifies to the excellent stability of the material against photodegradation.
Applied Physics Letters 12/2005; 87(26):261917-261917-3. · 3.84 Impact Factor
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ABSTRACT: Time-resolved photoluminescence spectroscopy experiments of three poly(2,8-indenofluorene) derivatives bearing different pendant groups are presented. A comparison of the photophysical properties of dilute solutions and thin films provides information on the chemical purity of the materials. The photophysical properties of poly(2,8-indenofluorene)s are correlated with the morphological characteristics of their corresponding films. Wide-angle X-ray scattering experiments reveal the order in these materials at the molecular level. The spectroscopic results confirm the positive impact of a new synthetic approach on the spectral purity of the poly(indenofluorene)s. It is concluded that complete side-chain substitution of the bridgehead carbon atoms C-6 and C-12 in the indenofluorene unit, prior to indenofluorene ring formation, reduces the probability of keto formation. Due to the intrinsic chemical purity of the arylated derivative, identification of a long-delayed spectral feature, other than the known keto band, is possible in the case of thin films. Controlled doping experiments on the arylated derivative with trace amounts of an indenofluorene-monoketone provide quantitative information on the rates of two major photophysical processes, namely, singlet photoluminescence emission and singlet photoluminescence quenching. These results allow the determination of the minimum keto concentration that can affect the intrinsic photophysical properties of this polymer. The data suggest that photoluminescence quenching operates in the doped films according to the Stern-Volmer formalism.
ChemPhysChem 09/2005; 6(8):1650-60. · 3.41 Impact Factor
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ChemPhysChem 08/2005; 6(7):1250-3. · 3.41 Impact Factor
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ABSTRACT: Photoluminescence properties of photoactive HBCC8,2 and HBCPt2 have been studied. The phenylene-ethynyl-Pt moieties were incorporated onto the bromo functions of HBCBr21 via double oxidative addition of Pt(PPh3)4 to 1 followed by CuI-catalyzed dehydrohalogenation reaction of compound 2 and phenylacetylene to give the desired molecule HBC-Pt2. Introduction of platinum-phenylacetylene to the hexa-peri-hexabenzocoronenes (HBC) core enhanced the spin–orbit coupling and decreased the phosphorescence lifetime of the triplet state by three orders of magnitude. Photoluminescence measurements revealed unique phosphorescence emission at room temperature and 77 K. On the other hand, symmetric HBC-C8,2, bearing no platinum, revealed different delayed emissions depending on the temperature measurement. At room temperature, delayed fluorescence appeared while at 77 K, only phosphorescence could be observed. The triplet energy level has been tuned between 2.3 and 1.7 eV by varying the HBC core substituents. In consequence, combination of both the heavy-atom effect and the increased intersystem crossing in the novel double platinum-substituted HBC lead to the exclusive emission of phosphorescence without any residues of fluorescence in the prompt and delayed emission spectra.
Synthetic Metals 156:1182-1186. · 1.83 Impact Factor
