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Different Conjugation Lengths (different + conjugation_length)
Selected AbstractsElectron-Rich Alcohol-Soluble Neutral Conjugated Polymers as Highly Efficient Electron-Injecting Materials for Polymer Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Fei Huang Abstract We report the design and synthesis of three alcohol-soluble neutral conjugated polymers, poly[9,9-bis(2-(2-(2-diethanolaminoethoxy) ethoxy)ethyl)fluorene] (PF-OH), poly[9,9-bis(2-(2-(2-diethanol-aminoethoxy)ethoxy)ethyl)fluorene- alt -4,4,-phenylether] (PFPE-OH) and poly[9,9-bis(2-(2-(2-diethanolaminoethoxy) ethoxy)ethyl)fluorene- alt -benzothiadizole] (PFBT-OH) with different conjugation length and electron affinity as highly efficient electron injecting and transporting materials for polymer light-emitting diodes (PLEDs). The unique solubility of these polymers in polar solvents renders them as good candidates for multilayer solution processed PLEDs. Both the fluorescent and phosphorescent PLEDs based on these polymers as electron injecting/transporting layer (ETL) were fabricated. It is interesting to find that electron-deficient polymer (PFBT-OH) shows very poor electron-injecting ability compared to polymers with electron-rich main chain (PF-OH and PFPE-OH). This phenomenon is quite different from that obtained from conventional electron-injecting materials. Moreover, when these polymers were used in the phosphorescent PLEDs, the performance of the devices is highly dependent on the processing conditions of these polymers. The devices with ETL processed from water/methanol mixed solvent showed much better device performance than the devices processed with methanol as solvent. It was found that the erosion of the phosphorescent emission layer could be greatly suppressed by using water/methanol mixed solvent for processing the polymer ETL. The electronic properties of the ETL could also be influenced by the processing conditions. This offers a new avenue to improve the performance of phosphorescent PLEDs through manipulating the processing conditions of these conjugated polymer ETLs. [source] Systematic Studies on Photoluminescence of Oligo(arylene-ethynylene)s: Tunability of Excited States and Derivatization as Luminescent Labeling Probes for ProteinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2006Yong-Gang Zhi Abstract Functionalized oligo(phenylene-ethynylene)s (OPEs) with different conjugation lengths, p -X(C6H4C,C)nSiMe3 (n = 1,4; X = NH2, NMe2, H) were synthesized by Sonogashira coupling of (phenylene-ethynylene)s and 1-iodo-4-(trimethylsilylethynyl)benzene, followed by desilylation of the p -substituted (trimethylsilylethynyl)benzenes with potassium hydroxide. The photoluminescent properties for the OPE series with different chain lengths and their solvatochromic responses were examined. The absorption maxima were red-shifted with increasing numbers of ,(C6H4C,C), units (n), and a linear plot of the absorption energy maxima vs. 1/n was obtained for each series. The emission spectra in dichloromethane showed a broad and structureless band, the energies of which (in wavenumbers) also fit linearly with 1/n. Both the absorption and emission wavelength maxima of the NH2 - and NMe2 -substituted OPEs exhibited significant solvent dependence, whereas the parent OPEs (X = H) showed only minor shifts of the ,max values in different solvents. Substituent effects upon the photoluminescent characteristics of the OPEs and the tunability of the excited states were examined with the p -X(C6H4C,C)nSiMe3 (n = 2, 3; X = NH2, NMe2, H, SMe, OMe, OH, and F) series. The H- and F-substituted counterparts exhibited high-energy vibronically structured emissions attributed to the 3(,,*) excited states of the (arylene-ethynylene) backbone. For compounds bearing NH2 and NMe2 groups, a broad red-shifted emission with a remarkable Stokes shift from the respective absorption maximum was observed, which can be assigned to an n , ,* transition. The n , ,* assignment was supported by MO calculations on the model compounds p -X(C6H4C,C)2SiH3 (X = NH2, H). Functionalization of the oligo(arylene-ethynylene)s with the N -hydroxysuccinimidyl (NHS) moiety enabled covalent attachment of the fluorophore to HSA protein molecules. A series of fluorescent labels, namely p -X(C6H4C,C)nC6H4NHS, (n = 1, X = NH2, NMe2, SMe, OMe, OH, F; n = 2, X = NH2, NMe2) and p -Me2NC6H4C,C(C4H2S)C,CC6H4NHS were synthesized, and their conjugates with HSA (human serum albumin) were characterized by MALDI-TOF mass spectrometry, UV/Vis absorption spectroscopy, and gel electrophoresis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Efficient blue-green-emitting poly[(5-diphenylamino-1,3-phenylenevinylene)- alt -(2,5-dihexyloxy-1,4-phenylenevinylene)] derivatives: Synthesis and optical propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2006Liang Liao Abstract New poly(phenylene vinylene) derivatives with a 5-diphenylamino-1,3-phenylene linkage (including polymers 2, 3, and 5) have been synthesized to improve the charge-injection properties. These polymers are highly photoluminescent with fluorescent quantum yields as high as 76% in tetrahydrofuran solutions. With effective ,-conjugation interruption at adjacent m -phenylene units, chromophores of different conjugation lengths can be incorporated into the polymer chain in a controllable manner. In polymer 2, the structural regularity leads to an isolated, well-defined emitting chromophore. Isomeric polymer 3 of a random chain sequence, however, allows the effective emitting chromophores to be joined in sequence by sharing a common m -phenylene linkage (as shown in a molecular fragment). Double-layer light-emitting-diode devices using 2, 3, and 5 as emitting layers have turn-on voltages of about 3.5 V and produce blue-green emissions with peaks at 493, 492, and 482 nm and external quantum efficiencies up to 1.42, 0.98, and 1.53%, respectively. In comparison with a light-emitting diode using 2, a device using 3 shows improved charge injection and displays increased brightness by a factor of ,3 to 1400 cd/m2 at an 8-V bias. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2307,2315, 2006 [source] Studies on the resonance Raman spectra of polyaniline obtained with near-IR excitation,JOURNAL OF RAMAN SPECTROSCOPY, Issue 7 2008Gustavo M. do Nascimento Abstract The effects of near-IR (NIR) laser power over the Raman spectra of poly(aniline) emeraldine salt (PANI-ES) and base (PANI-EB) were investigated. The reasons for the existence of several bands from 1324 to 1500 cm,1 in the Raman spectra of poly(aniline) obtained at NIR region were also studied. The bands from 1324 to 1375 cm,1 were associated to ,CN of polarons with different conjugation lengths and the bands from 1450 to 1500 cm,1 in Raman spectra of PANI emeraldine and pernigraniline base forms were correlated to ,CN modes associated with quinoid units having different conjugation lengths. The increase of laser power at 1064.0 nm causes the deprotonation of PANI-ES and the formation of cross-linking segments having phenazine and/or oxazine rings. For PANI-EB only a small spectral change is observed when the laser power is increased, owing to the low absorption of this form in the NIR region. Copyright © 2007 John Wiley & Sons, Ltd. [source] | |||||||||||||