Filtern
Erscheinungsjahr
Dokumenttyp
- Vortrag (80)
- Zeitschriftenartikel (27)
- Beitrag zu einem Sammelband (7)
- Beitrag zu einem Tagungsband (5)
- Posterpräsentation (3)
- Buchkapitel (1)
- Sonstiges (1)
Schlagworte
- Chemiluminescence (4)
- Oxidation (2)
- Ashby-Diagramme (1)
- Bromierung (1)
- Bromination (1)
- Chemilumineszenz (1)
- Chlorination (1)
- Conjugated polymer (1)
- Dendrimers (1)
- Diphenylethylenderivate (1)
Eingeladener Vortrag
- nein (80)
Über Innovation
(2007)
Zwischen Chemie, Wirtschaft und Politik - Aus den Aufgaben einer Chemisch-Technischen Bundesanstalt
(1995)
Werkstoffe
(2012)
Intrinsically conductive plasma polymers were formed in a 2.45 GHz microwave low pressure plasma. The electrical conductivity and structure of the polymeric films were compared with those of electrochemically polymerized polythiophene. A new method of doping was tested using the iodine-containing monomer 2-iodothiopene. Films with high electrical conductivity (10-1 down to 10-6 S cm-1) could be produced, and their chemical structure was studied by X-ray photoelectron spectroscopy and Fourier transform IR spectroscopy. The IR spectra give a strong indication that the chemical structure of these films is comparable with that of electrochemically deposited polythiophene. Optical emission spectroscopy was used to give in-situ information about the fragmentation mechanism in the plasma.
Conjugated polymers based on 1,4-phenylenevinylene units are very promising materials for applications as light-emitting diodes. A major requirement is their stability at elevated temperatures of operation. The thermo-oxidative behaviour of a soluble poly(1,4-phenylenevinylene) derivative, poly[2,5-bis(2-ethylhexyloxy)-1,4-phenylene vinylene], was investigated by using chemiluminescence and UVVis absorption spectroscopy. Extremely sensitive chemiluminescence is successfully applied since even minor chemical changes could lead to a considerable loss of photo- and electro-optical properties. Various degradation processes are described as a function of time and temperature and their influences on functional properties are discussed. The investigated material does not show sufficient thermo-oxidative stability within the temperature range of intended use in contact with air. For industrial application, direct contact with oxygen during processing and operation has to be avoided.
Structural investigations of electrical conducting plasma polymerized films from 2-iodothiophene
(1993)
Thin plasma polymerized films were produced in a microwave (2.45 GHz) plasma discharge using 2-iodothiophene as the initial monomer. The structure of these electrically conducting films (10-6-10-1 S/cm), the chemical state of the doping element iodine and the elemental homogeneity at the surface and in the films have been investigated by XPS, FTIR and AES. An interesting relationship was found that indicates some similarity to conventional polythiophene, prepared by electrodeposition. Besides covalently bound iodine, considerable amounts of I 3- and I 5- were detected and also a small number of O-I bonds were identified.
Fast allen deutschen Bundesministerien sind Einrichtungen zugeordnet, die sie in der Erfüllung von Bundesaufgaben auf wissenschaftlicher Grundlage unterstützen. Die Vielfalt sowie die Art und der jeweilige Anteil der Aufgaben (insbesondere der Anteil der Forschung) haben dazu geführt, das es sehr unterschiedliche Typen von Ressortforschungseinrichtungen gibt. Viele dieser Einrichtungen erbringen in bedeutendem Umfang Dienstleistungen für Wirtschaft, Wissenschaft und Gesellschaft; alle stehen den Ministerien für Beratungsaufgaben unmittelbar zur Verfügung. Ihre Kompetenz stützt sich ganz wesentlich auf Forschung und Entwicklung und unterscheidet sie dadurch von anderen Bundesbehörden.
Polarized fluorescence and orientational order parameters of a liquid-crystalline conjugated polymer
(1999)
We report a study of the orientational order of aligned thin films of the liquid crystalline conjugated polymer poly(9,9-dioctylfluorene). Steady state polarized fluorescence measurements were used to determine the orientational order parameter <P2> and <P4>. The influence of intermolecular and intramolecular excitation energy transfer on the degree of polarization is discussed. The role of film morphology is also examined by comparison of the results for glassy and crystalline films.
Polarized fluorescence and orientational order parameters of a liquid crystalline conjugated polymer
(1999)
In films of poly(para-phenylphenylenevinylene) a photoreaction has been observed. The significant feature is a decrease of the fluorescence emission intensity during irradiation. It is assumed that a cycloaddition between C=C- double-bonds leads to crosslinks in the material.
Under similar conditions of excitation a photoreaction has not been observed in poly(p-phenylenevinylene) prepared via the precursor-route.
Stationary polarized fluorescence spectra of poly(1,4-phenylene-1-phenylvinylene), poly(1,4-phenylene-1,2-diphenylvinylene) and poly[1,4-phenylene-1,2-bis(4-phenoxyphenyl)vinylene] in tetrahydrofuran solution and in polystyrene films were recorded at room temperature. In these matrices, different behaviour is found concerning the Stokes shift, the degree of polarization and the quantum yield; it is interpreted as a viscosity induced effect. The commonly accepted model of a conjugated polymer chain to consist of independent segments of various length should not be applied to the poly(phenylene-arylvinylene)s studied in this work.
Photo- and thermo-oxidative stability of aromatic spiro-linked bichromophoric cross-shaped molecules
(2000)
An extensive investigation of the photostability and the thermo-oxidative stability is presented for 2,2,7,7-tetrakis(biphenyl-4-yl)-9,9-spirobifluorene and 2,2,4,4,7,7-hexakis(biphenyl-4-yl)-9,9-spirobifluorene. Both compounds are conjugated fully aromatic systems that are being discussed as active functional materials for a variety of advanced applications. The effect of atmosphere, sample thickness and preparation procedure on photo-oxidative degradation are investigated in detail by absorption and fluorescence spectroscopy. Distinct mechanisms are described in terms of relevant parameters such as the quantum yields of the photo-oxidation and the fluorescence. No oxidative degradation could be detected under nitrogen. In ambient air a strong decrease of the fluorescence performance is found due to effective quenching by defective chromophores. Chemiluminescence investigations were performed to characterise the thermo-oxidative behaviour in the temperature region between 300 and 450 K. It becomes clear that even a stable chemical structure such as the investigated aromatic system does not guarantee sufficient photostability with regard to light emitting properties.
About this Journal
Measurements of polarized excitation and fluorescence spectra were carried out with thin films of PPV and with films of oligomer model compounds in a polystyrene matrix. The degree of fluorrescece polarization r and its spectral dependence are discussed with respect to the transfer of excitation energy and the mutual alignment of the flurophores. In contrast to the behaviour of conventional aromatic polymers, the value of r is non-zero in isotropic PPV and depends on preparation (up to r = 0.25 at λexc = 460 nm and λflu = 555 nm). r can be nearly as high as in the dilute solid solution of the oligomers. This is easily understood if the PPV segments are highly aligned in the distance range of energy transfer.
On the thermal behaviour and thermo-oxidative stability of liquid crystalline triphenylene compounds
(1999)
Columnar discotic materials are considered for applications in the area of photoconductivity and light-emitting diodes. A major requirement is their stability at elevated temperatures and in the presence of oxygen. The thermal and thermo-oxidative behaviour of discotic triphenylene derivatives was investigated by us using various methods, in particular by chemiluminescence (CL), UV-vis absorption spectroscopy and in situ thermogravimetry-mass spectroscopy (TG-MS). Various degradation processes are described for increasing temperature, and their influences on functional properties are discussed.
If the intramolecular distance between the two isoenergetic chromophores of a bichromophoric compound is much smaller than the Förster radius of excitation energy transfer (EET), the probability to fluoresce is equal for both chromophores, because the EET takes place at a shorter time compared with the nanosecond timescale of the fluorescence lifetime. Then, the fluorescence depolarization of diluted solid solutions of such bichromophoric molecules can be measured with stationary excitation and used to evaluate the orientation between the two chromophores; in the most simple case the angle between their main axes is determined. Model calculations for bichromophoric alkane compounds with various conformational freedom reveal the amount of depolarization and thus the limits of the method. The results are compared to experimental data of 1,3-di(N-carbazolyl)-propane and 1,2-trans-di(N-carbazolyl)cyclobutane.
Nanoscience in der BAM
(2011)