Cornelia Bader

Amplified spontaneous emission in neat films of arylene-vinylene polymers

Amplified spontaneous emission (travelling-wave lasing) was achieved for a set of 18 poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) related arylene-vinylene copolymers, a part of which substituted with additional phenyl groups at the vinyl double bond. Wave-guiding neat thin films on glass substrates were used. The samples were transversally pumped with single second harmonic pulses of a mode-locked ruby laser (wavelength 347.15 nm). Travelling-wave emission occurred in the wavelength region between 485 and 650 nm. Repeat unit based absorption cross-section spectra, normalized fluorescence quantum distributions, and amplified spontaneous emission spectra are presented. Ground-state absorption cross-sections at the wavelengths of peak amplified emission are extracted from effective gain length measurements. Effective stimulated emission cross-sections are derived from pump pulse energy densities necessary for optical narrowing.

Synthesis and characterization of three types of alkoxy-substituted hybrid PPV-PPE polymers: Potential candidates for photovoltaic applications

Polymers of general constitutional structures: (formula available in paper) have been synthesized through the Horner- Wadsworth-Emmons olefination reactions of bisphosphonates 3 and fluorophoric dialdehydes 1, 2, 12 and 13 respectively. High molecular-weight, thermostable and transparent film-forming materials were obtained in high yields. The new compounds exhibit lyotropic and thermotropic liquid crystalline behavior. The insertion of triple bonds into the conjugated backbone enhances the electronaffinity relative to PPV and make them highly luminescent in solution as well as in solid state. Fluorescence quantum yields between 60 and 80% in solution and between 20 and 50% in film and extinction coefficients around 100,000 M-1cm-1 were obtained. In the cases of 4 and 5 are the solid state properties side - chains dependent. The three classes of polymers 5, 14 and 15 show similar photoluminescence behavior despite the differences in constitutional structures. This can be ascribed to identical chromophore system responsible for the emission. They are presently used in the design of light-emitting diodes and organic solar cells devices.

MEH-PPV and thianthrene-containing PPV-derivatives as efficient polymeric materials for solid-state lasers

Using the methodology of traveling-wave lasing in neat films (amplified spontaneous emission, ASE) we have investigated the novel polycondensation-type MEH-PPV 1(strictly linear and fully conjugated) and some of its alternating copolymer combinations with 2,5-dialkoxy-phenylenevinylene (2-5) and thianthrene-vinylene (6-8) units. Well-defined, solution- processable, high-molecular weight samples (Mw = 20.000 - 60.000) have been prepared via the polycondensation route employing the repetitive HORNER carbonyl-olefination. This is based on the reaction of appropriate xylylene bis(phosphonates) with dialkoxy-substituted phenylene dialdehydes and dibenzoyl-thianthrene (dibenzoyl-benzene), respectively. In previous studies Thianthrene-PPVs were reported to display green EL from single layer devices while the dialkoxy-PPVs are known to display orange or red EL. Here, traveling-wave lasing studies are performed on neat films. Solution cast amorphous film samples on glass substrates are transversally pumped with picosecond laser pulses (wavelength 347 nm, duration 35 ps). Lasing occurs at 622 nm for MEH-PPV 1, 646 nm (M3EH-PPV 2), 629 nm (MEH- DOO-PPV 3), 629 nm (DMO-DO18-PPV 4), 522 nm (Thianthrene- MEH-PPV 7) and at 647 nm and 630 nm for the new M3EH-OPV containing terpolymers (DP-MEH-OPV)0,25n(M3EH-OPV)0,75n5 and (Thianthrene-MEH-OPV)o,5n(M3EH-OPV(0,5n8, respectively. The spectral widths of emission are less than 13 nm. Laser threshold energy densities are found to be rather low, ranging between 4 and 18(mu) jcm-2. The effective lengths of amplification are roughly 1 mm. These results show that all the condensation polymers under investigation are good solid-state laser materials for optically pumped disk, ring and DFB lasers and that they are potential candidates for electrically pumped lasers. Furthermore, it is demonstrated that amorphous blends of the polycondensation-type MEH-PPV 1 with the electroactive DPOP- PPV (ratio 50:50, 30:70 p. wt.) Or Thianthrene-MEH-PPV 7 (ratio 50:50, 22:78 and 5.6:94.4 p. wt.) exhibit red ASE around 590 - 615 nm as the result of energy (exciton) transfer from the green emitting donor materials to the MEH- PPV acceptors.

Travelling-wave lasing in neat films of arylene-vinylene polymers

Amplified spontaneous emission (travelling-wave lasing) was achieved for a series of arylene-vinylene polymers (PAy). Wave-guiding neat films on glass substrates were used. The samples were transversally pumped with picosecond laser pulses (wavelength 347. 1 5 nm, duration 35ps). The laser emission occurred in the wavelength region between 480 nm and 650 nm. The travelling-wave lasing was identified by spectral narrowing, temporal shortening, and threshold behavior of light emission.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Combinatorial screening of inkjet printed ternary blends for organic photovoltaics: absorption behavior and morphology.

Inkjet printing was used for the preparation of ternary polymer/polymer/fullerene layers for organic solar cell application, as part of a combinatorial setup for the preparation and characterization of thin-film libraries. Poly(phenylene-ethynylene)-alt-poly(phenylene-vinylene) (PPE-alt-PPV) and poly(diketopyrrolopyrrole-alt-fluorene) (P(DPP-alt-F)) were systematically blended with poly(3-octylthiophene) (P3OT) and investigated by UV-vis spectroscopy to improve the photon harvesting by extending the absorption range. The blends with the broadest absorption range (20 and 40 wt % of PPE-alt-PPV and P(DPP-alt-F), respectively) were mixed with mono(1-[3-(methoxycarbonyl)propyl]-1-phenyl)-[6,6]C61 (PCBM). The blend with the low band gap polymer P(DPP-alt-F) revealed the most extended absorption, which ranges over the whole visible spectrum (350 to 750 nm). The mixing with PCBM (ratio 1/3) led to an optimal emission quenching and revealed a smooth film formation. In this contribution, we show that the combinatorial screening using inkjet printing represents an effective, time- and material-saving workflow for the investigation of polymer blend libraries, which is of high interest for the development of new materials for active layers in organic photovoltaics.

Photophysical and lasing characterization of neat films of 4-methyl-TPD and of a 4-methyl-TPD phenyl substituted MEH-PPV copolymer

Wave-guided travelling-wave lasing (amplification of spontaneous emission in waveguide) is studied on neat films of the triphenylamine dimer 4-methyl-TPD, and of the 4-methyl-TPD phenyl substituted MEH-PPV copolymer TPD(4M)-MEH-P-PPV. Laser action is achieved by transverse pumping neat films on glass substrates with picosecond excitation pulses (wavelength 347.15 nm, duration 35 ps). Lasing occurs at 422 nm for 4-methyl-TPD and at 544 nm for TPD(4M)-MEH-P-PPV. The optical constants (absorption spectra and refractive index spectra), the absorption cross-section spectra, fluorescence quantum distributions, fluorescence quantum yields, and fluorescence lifetimes of the samples are determined for photo-physical characterization. The laser performance and the photo-physical parameters of 4-methyl-TPD and TPD(4M)-MEH-P-PPV are compared with results on MEH-PPV.

Photocontrolled Release of Chemicals from Nano‐ and Microparticle Containers

A benzoin-derived diol linker was synthesized and used to generate biocompatible polyesters that can be fully decomposed on demand upon UV irradiation. Extensive structural optimization of the linker unit was performed to enable the defined encapsulation of diverse organic compounds in the polymeric structures and allow for a well-controllable polymer cleavage process. Selective tracking of the release kinetics of encapsulated model compounds from the polymeric nano- and microparticle containers was performed by confocal laser scanning microscopy in a proof-of-principle study. The physicochemical properties of the incorporated and released model compounds ranged from fully hydrophilic to fully hydrophobic. The demonstrated biocompatibility of the utilized polyesters and degradation products enables their use in advanced applications, for example, for the smart packaging of UV-sensitive pharmaceuticals, nutritional components, or even in the area of spatially selective self-healing processes.