Dietrich Raabe

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 of TPD-containing polymers for use as light emitting materials in electroluminescent and Laser devices

The synthesis of two families of electrically active and highly luminescent TPD-based copolymers is reported. (1) The Horner-olefination between TPD-dialdehydes and xylylene bisphosphonates has been used to prepare red and green emitting conjugated TPD-PPV copolymers 1 - 4. Here the TPD (triphenylamine dimer) moieties are brigded through alkoxy- substituted p-phenylene vinylene segments. (2) Blue emitting, nonconjugated TPD-xylylene copolymers (Poly-TPD- DPX 5, (6) have been synthesized by an electrophilic aralkylation using diphenylxylylene diol and TPD as the monomers. All these TPD-copolymers constitute amorphous electro-optical materials possessing remarkably high glass transition temperatures (Tg 110 - 240 degrees Celsius). Here we demonstrate strong lasing in the red, green and blue spectral region employing thin layers (approximately 100 nm) of these solution processable polymeric materials. In waveguiding neat films traveling-wave lasing (amplified spontaneous emission -- ASE) is achieved upon picosecond pulse excitation at 347 nm. Pump energy density thresholds as low as 3 (mu) J/cm2 and ASE-line halfwidths approximately 10 nm have been observed. Comparable to the typical redox behavior of free TPD molecule the novel TPD- based polymers exhibit fully reversible electron transfer at low potential (EOx approximately 0.65 V), which is favorable for hole injection and stable charge transport in the semiconducting organic materials. In addition, these high-Tg polymers can act as the electro-active materials in LEDs, photovoltaic cells and photorefractive devices. The waveguiding properties of Poly-TPD-DPX were determined in planar and strip waveguides to be 12 dB/cm at 640 nm, and 2 dB/cm at 1550 nm.

Photo-physical and lasing characterization of an aromatic diamine-xylylene copolymer

A solution processable poly-condensation product of high glass transition temperature containing 50 mol% electrically active triphenylamine dimer (TPD) chromophores and 50 mol% non-conjugated α,α-diphenylxylylene (DPX) units in the main chain is studied for its photo-physical and lasing properties. This copolymer abbreviated as poly-TPD-DPX shows travelling-wave laser action (amplification of spontaneous emission) as neat film on a fused silica substrate and in liquid solution when transversally pumped with picosecond excitation pulses (wavelength 347.15 nm, duration 35 ps). Lasing occurs at 419 nm for the neat film and at 405 nm for the polymer in 1,4-dioxane solution. The optical constants (absorption spectrum and refractive index spectrum) of the neat film are determined by reflection and transmission measurement. The absorption cross-section spectra and fluorescence quantum distribution spectra of neat films and 1,4-dioxane solutions are compared. The fluorescence quantum yields of poly-TPD-DPX neat films and 1,4-dioxane solutions are 0.16 and 0.66, respectively.

Photo-physical characterisation and travelling-wave lasing of some TPD-based polymer neat films

Abstract Travelling-wave lasing (amplification of spontaneous emission) is reported for neat films of a series of five red, green and blue emitting TPD-based polymers, the TPD-phenylenevinylene and the TPD-xylylene copolymers. Thin samples on glass substrates were fabricated by spin-coating and transversally pumped with picosecond excitation pulses (wavelength 347.15 nm, duration 35 ps). Lasing occurs around 421, 536, 540, 571, and 618 nm with a line-width smaller than 10 nm. The threshold pump pulse energy densities are determined and found to be 60 μJ / cm 2 for the blue emitting non-conjugated polymer (Poly-TPD(4M)-DPX) and 6–8 μJ / cm 2 for the green and red emitting conjugated polymers TPD(4M)-MEH-PPV and TPD(4M)-MEH-M3EH-PPV. The laser output saturation at high excitation energy densities is studied. The length of effective amplification of spontaneous emission is approximately 1 mm. Effective stimulated emission cross-sections are derived from the pump pulse energy density dependent spectral narrowing of the amplified emission signals. The optical constants (absorption spectrum and refractive index spectrum) of the neat films are determined by reflection and transmission measurements. The absorption cross-section spectra are extracted. The fluorescence quantum efficiencies and the fluorescence lifetimes are measured.

Syntheses and Properties of Cycloamidines Based on 4H-Imidazoles*

Employing three different syntheses a broad spectrum of 4H-imidazoles 3a - 3s has been synthesized. In the course of the two-fold aminolysis reaction leading to derivatives 3q - 3s, deeply colored byproducts could be isolated and structural characterized.These novel donor-acceptor derivatives of type 7 consist of an 1H- and 4H-imidazole which are connected by a nitrogen bridge and rearrange via rapid 1,3-/1,5-hydride shifts. Using 1H NMR experiments the aminolysis product 3p shows prototropic isomers which could be detected in equilibrium for the first time. Cyclovoltammetric measurements of a series of substituted 2-aryl derivatives 3d - 3i displayed two reversible single electron transfer steps with relatively small semiquinone formation constants between 102 and 4×103. The 4H-imidazole 3d was successfully converted into boratetraaza-pentalene 8a, which showed two well separated reduction potentials. The value of semiquinone formation constant of 8a (1.8×1015) is even higher than those reported for similar derivatives. 4H-imidazoles can also be employed for the efficient complexation of catalytically important metals as exemplified by copper complexes 11 and 12. Derivative 3m, which possesses an additional chelating pyridine substructure, formed a stable complex of structural composition Zn(3m)2 with diethyl zinc

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.