			Home About us Contact

Effective Conjugation Length (effective + conjugation_length)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

The Influence of UV Irradiation on Ketonic Defect Emission in Fluorene-Based Copolymers,

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2008
Horst Scheiber
Abstract The influence of UV irradiation in inert atmosphere on the emission spectrum of fluorenone containing poly[9,9-bis(2-ethyl)hexylfluorene] (PF2/6) has been investigated by means of optical absorption, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. It is shown that a substantial reduction of green emission arising from ketonic defect sites can be achieved by irradiation of thin films with UV light. This is found to be accompanied by partial cross-linking of the films. FTIR measurements show no reduction of the C=O stretching mode upon irradiation, and, moreover, the degree of cross-linking does not scale with the relative fluorenone content (0.1, 0.5, and 5%). Therefore, the reduced emission intensity in the green spectral region is rather associated with the occurrence of interruptions in the polymer backbone, which reduce the effective conjugation length and subsequently inhibit the energy transfer onto the ketonic defect sites. The found results enabled us to build organic light emitting devices (OLEDs) that can be structured by selective illumination of the emitting layer with an intense UV light source. This method allows for the fabrication of rather efficient (2000,cd,m,2 at 7,V) two-color OLEDs. [source]

Hyperbranched copolymer containing triphenylamine and divinyl bipyridyl units for fluorescent chemosensors

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2009
Jichang Feng
Abstract A fluorescent hyperbranched copolymer (HTP) and a linear copolymer (PTP) as a reference sample to HTP both containing triphenylamine and divinyl bipyridyl units were synthesized via Heck coupling reaction from 5,5,-Divinyl-2,2,-bipyridyl with tris(4-bromophenyl)amine and with 4,4,-dibromotriphenylamie, respectively. The chemical structure of HTP was confirmed by FTIR, 1H NMR, and 13C NMR. The polymer HTP had a number-average molecular weight of 1895 and a weight-average molecular weight of 2315, and good solubility in conventional organic solvents, such as THF, DMF, and chloroform, and exhibited good thermal stability. The UV,vis absorption and photoluminescence (PL) spectra exhibited absorption maximum at 428 nm and emissive maximum at 531 nm for the HTP solution. The spectroscopic results of HTP and PTP indicated that hyperbranched conjugated structure increases the effective conjugation length, as compared with corresponding linear conjugated structure. The fluorescence of the polymer in solution can be quenched by various transition metal ions. The effect of backbone structure of the conjugated polymer-based chemosensors on the sensitivity and selectivity in metal ions sensing have been investigated, and the quenching effect of HTP is more sensitive toward transition metal than linear copolymer PTP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 222,230, 2009 [source]

Temperature dependence of intra-chain photoluminescence of a long oligothiophene

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009
Katsuichi Kanemoto
Abstract The temperature dependence (4 K-300 K) of the photoluminescence (PL) and absorption spectra of 16-mer oligothiophene (16T) diluted in polypropylene (PP) with a weight ratio of 1/30000 has been investigated in order to clarify the intrinsic temperature effect on conjugated polymers with negligible interchain interaction. The PL and absorption spectra are found to blueshift with increasing temperature. Simple model calculations suggest that the effective conjugation length of 16T is reduced to the two-third of the original chain length at room temperature. The magnitude of Stokes shift of 16T increases with increasing temperature. The steady-state PL spectra can be well reproduced by spectral fitting based on Franck-Condon analysis using a single Huang-Rhys (HR) factor over the wide temperature range of the measurement. This analysis demonstrates the temperature dependence of HR factor in PL. The HR factor in PL is found to decrease with increasing temperature, whereas that of the absorption spectra increases with temperature. This observation can be explained by assuming that the lowest energy conformer of 16T is responsible for PL and such a conformer has smaller coupling with phonons. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Synthesis and Electronic Properties of Monodisperse Oligophenothiazines

CHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2008
Markus Sailer Dr.
Abstract Starting from N -hexylphenothiazine, a versatile construction kit of brominated and borylated phenothiazines can be easily prepared by a sequence of bromination, bromo,lithium exchange/borylation, and Suzuki coupling. Subsequent Suzuki arylation of the building blocks gives soluble, monodisperse, and structurally well defined oligophenothiazines in good yields. The molecular weights at the peak maximum (Mp), obtained by GPC (gel permeation chromatography), and the actual molecular weights of the oligomer series, obtained by mass spectrometry, show excellent correlation. A QM/MM conformational analysis for the complete series reveals that the obvious butterfly-shaped phenothiazine structure multiplies and significantly reduces the hydrodynamic volume of the oligomers. The electronic properties (absorption and emission spectroscopy and cyclic voltammetry) give reasonable correlations with the chain length. With regard to the emission maxima, the effective conjugation length is already reached with the hexamer. Oligophenothiazines are highly fluorescent, with high fluorescence quantum yields, and are simultaneously highly electroactive, with low oxidation potentials. Ausgehend von N -Hexylphenothiazin kann leicht ein vielseitiger Baukasten aus bromierten und borylierten Phenothiazinen über eine Sequenz aus Bromierung, Bromo,Lithium-Austausch/Borylierung und Suzuki Kupplung hergestellt werden. Die nachfolgende Suzuki-Arylierung der Bausteine führt in guten Ausbeuten zu löslichen, monodispersen und strukturtreuen Oligophenothiazinen. Die Molekulargewichte beim Peakmaximum (Mp), die aus GPC (Gelpermeationschromatographie) erhalten werden und die tatsächlichen Molekulargewichte der Oligomeren, erhalten durch Massenspektrometrie, ergeben eine exzellente Korrelation. Die QM/MM-Konformationsanalyse der gesamten Serie zeigt, das der Effekt der Schmetterlingsstruktur der Phenothiazine sich vervielfältigt und so das hydrodynamische Volumen der Oligomere deutlich verkleinert. Die elektronischen Eigenschaften der Oligomere (Absorptions- und Emissionsspektroskopie und Cyclovoltammetrie) korrelieren mit der Kettenlänge. Im Falle der Emissionsmaxima wird die effektive Konjugationslänge bereits mit dem Hexamer erreicht. Oligophenothiazine fluoreszieren mit hohen Fluoreszenzquantenausbeuten und erweisen sich gleichzeitig wegen ihrer niedrigen Oxidationspotenziale als äußerst elektroaktiv. [source]