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Conjugated Backbone (conjugated + backbone)
Selected AbstractsElectrophosphorescent Polyfluorenes Containing Osmium Complexes in the Conjugated Backbone,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2008Chen-Han Chien Abstract Electrophosphorescent copolymers have been synthesized by covalent bonding of a red-emitting osmium complex Os(bpftz), which contains two 3-trifluoromethyl-5-(4- tert -butyl-2-pyridyl)triazolate (bpftz) cyclometalated ligands, into the backbone of a bipolar polyfluorene (PF) copolymer. Employing these copolymers, a highly efficient red polymer light-emitting diode has been realised that has an external quantum efficiency of 18.0%, a maximum brightness of 38,000,cd,m,2, and an emission centered at 618,nm. In addition, after incorporating appropriate amounts of green-emitting benzothiadiazole (BT) and the aforementioned Os(bpftz) into the bipolar PF, an efficient white-light electroluminescent polymer is obtained that displays simultaneous blue, green, and red emissions. [source] Intercalating Dye Harnessed Cationic Conjugated Polymer for Real-Time Naked-Eye Recognition of Double-Stranded DNA in SerumADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Kan-Yi Pu Abstract Thiazole orange (TO), an intercalating dye, is integrated into cationic poly(fluorene- alt -phenylene) (PFP) to develop a macromolecular multicolor probe (PFPTO) for double-stranded DNA (dsDNA) detection. This polymer design not only takes advantage of the high affinity between TO and dsDNA to realize dsDNA recognition in biological media, but also brings into play the light-harvesting feature of conjugated polymers to amplify the signal output of TO in situ. PFPTO differentiates dsDNA from single-stranded DNA (ssDNA) more effectively upon excitation of the conjugated backbone relative to that upon direct excitation of TO as a result of efficient fluorescence resonance energy transfer from the polymer backbone to the intercalated TO. In the presence of dsDNA, energy transfer within PFPTO is more efficient as compared to that for free TO/PFP system, which leads to better dsDNA discriminability for PFPTO in contrast to that for TO/PFP. The distinguishable fluorescent color for PFPTO solutions in the presence of dsDNA allows naked-eye detection of dsDNA with the assistance of a hand-held UV lamp. The significant advantage of this macromolecular fluorescent probe is that naked-eye detection of label-free dsDNA can be performed in biological media in real-time. [source] The Influence of Alkyl-Chain Length on Beta-Phase Formation in PolyfluorenesADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Daniel W. Bright Abstract Di- n -alkyl substituted polyfluorenes with alkyl chain lengths of 6, 7, 8, 9, and 10 carbon atoms (PF6, PF7, PF8, PF9, and PF10) are studied in dilute solution in MCH using optical spectroscopy. Beta-phase is formed upon cooling in solutions (, 7,µg mL,1) of PF7, PF8, and PF9 only, which is observed as an equilibrium absorption peak at , 437,nm and strong changes in the emission spectra. Beta-phase is formed upon thermal cycling to low temperature in solutions (,7,µg mL,1) of PF7, PF8, and PF9, which is observed as an equilibrium absorption peak at , 437,nm and strong changes in the emission spectra. Beta phase is found to occur more favorably in PF8 than in PF7 or PF9, which is attributed to a balance between two factors. The first is the dimer/aggregate formation efficiency, which is poorer for longer (more disordered) alkyl chain lengths, and the second is the Van der Waals bond energy available to overcome the steric repulsion and planarize the conjugated backbone, which is insufficient in the PF6 with a shorter alkyl chain. Beta phase formation is shown to be a result of aggregation, not a precursor to it. A tentative value of the energy required to planarize the fluorene backbone of (15.6,±,2.5) kJ mol,1 monomer is suggested. Excitation spectra of PF6, PF7, PF8, and PF9 in extremely dilute (, 10,ng mL,1) solution show that beta phase can form reversibly in dilute solutions of PF7, PF8 and PF9, which is believed to be a result of chain collapse or well dispersed aggregates being present in solution from dilution of more concentrated solutions. PF7, PF8, and PF9 also form beta phase in thermally cycled solid films spin-cast from MCH. However, in the films the PF7 formed a larger fraction of beta phase than the PF9, in contrast to the case in solutions, because it is less likely that the close-packed chains in the solid state will allow the formation of planarized chains with the longer PF9 side chains. [source] Side-Chain Degradation of Ultrapure ,-Conjugated Oligomers: Implications for Organic ElectronicsADVANCED MATERIALS, Issue 5 2009Robert Abbel The degradation of two defect-free, -conjugated oligomers, and the participation of their solubilizing side chains in the process are studied in unprecedented detail. The detected intermediate products reveal a mechanism of successive shortening of alkyl and oligo(ethylene glycol) substituents. Eventually, these processes cause chemical modifications in the conjugated backbone, which strongly influence the electronic properties of the materials. [source] Persistent and emission color tunable poly(phenylene-ethynylene)s covered with polyhedral oligomeric silsesquioxanesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2008Junpei Miyake Abstract The development of chemically and thermally persistent blue-, and green-luminescent hybrid ,-conjugated polymers consisting of poly(phenylene-ethynylene) conjugated backbone wrapped with the rigid three-dimensional polyhedral oligomeric silsesquioxane (POSS) units was successfully achieved by means of the Sonogashira-Hagihara coupling reaction. Because of the steric effect of POSS units, the luminescence stability of the conjugated backbone was significantly enhanced. Moreover, emission color was also easily tunable only by changing the ratio of POSS moieties incorporated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8112,8116, 2008 [source] Luminescence properties of poly- (phenylene vinylene) derivativesPOLYMER INTERNATIONAL, Issue 3 2008Cuong Ton-That Abstract BACKGROUND: Conjugated polymers, especially those of the poly(phenylene vinylene) (PPV) family, are promising candidates as emission material in light-emitting devices. The aim of this work was to investigate the dependence of the luminescence properties of PPV-based derivatives on their polymer structure, especially side groups. RESULTS: Three PPV derivatives, BEHPPV, MEHPPV and MEHSPPV, were synthesised and characterised by photoluminescence (PL) and cathodoluminescence (CL) spectroscopies in the temperature range 10,300 K. PL and CL spectra of the polymers exhibit similar luminescence peaks, which undergo a blue shift with increasing temperature. The shift in wavelength is accompanied by variations in the relative intensities of emission peaks. Both BEHPPV and MEHPPV display emission characteristics of the PPV backbone, but the peak of MEHPPV shifts to a longer wavelength in comparison with the corresponding peak of BEHPPV at the same temperature. The luminescence spectra of MEHSPPV, which has a sulfanyl incorporated in the side chain, are considerably different from those of the two other derivatives. CONCLUSIONS: The results demonstrate that the luminescence properties depend strongly on the chain conformations of the conjugated backbone, which are affected by polymer side chains. Copyright © 2007 Society of Chemical Industry [source] Neutral and Oxidized Triisopropylsilyl End-Capped Oligothienoacenes: A Combined Electrochemical, Spectroscopic, and Theoretical StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2010Juan Aragó Abstract This work presents an analysis of the structural, electrochemical, and optical properties of a family of triisopropylsilyl end-capped oligothienoacenes (TIPS- Tn -TIPS, n=4,8) by combining cyclic voltammetry, spectroscopic techniques, and quantum-chemical calculations. TIPS- Tn -TIPS compounds form stable radical cations, and dications are only obtained for the longest oligomers (n=7 and 8). Oxidation leads to the quinoidization of the conjugated backbone, from which electrons are mainly extracted. The absorption and fluorescence spectra show partially resolved vibronic structures even at room temperature, due to the rigid molecular geometry. Two well-resolved vibronic progressions are observed at low temperatures due to the vibronic coupling, with normal modes showing wavenumbers of ,1525 and ,480,cm,1. Optical absorption bands display remarkable bathochromic dispersion with the oligomer length, indicative of the extent of , conjugation. The optical properties of the oxidized compounds are characterized by in situ UV/Vis/NIR spectroelectrochemistry. The radical cation species show two intense absorption bands emerging at energies lower than in the neutral compounds. The formation of the dication is only detected for the heptamer and the octamer, and shows a new band at intermediate energies. Optical data are interpreted with the help of density functional theory calculations performed at the B3LYP/6-31G** level, both for the neutral and the oxidized compounds. [source] Single-Molecule Spectroscopy on a Ladder-Type Conjugated Polymer: Electron,Phonon Coupling and Spectral DiffusionCHEMPHYSCHEM, Issue 14 2009Richard Hildner Dr. Abstract We employ low-temperature single-molecule spectroscopy combined with pattern recognition techniques for data analysis on a methyl-substituted ladder-type poly(para -phenylene) (MeLPPP) to investigate the electron,phonon coupling to low-energy vibrational modes as well as the origin of the strong spectral diffusion processes observed for this conjugated polymer. The results indicate weak electron,phonon coupling to low-frequency vibrations of the surrounding matrix of the chromophores, and that low-energy intrachain vibrations of the conjugated backbone do not couple to the electronic transitions of MeLPPP at low temperatures. Furthermore, these findings suggest that the main line-broadening mechanism of the zero-phonon lines of MeLPPP is fast, unresolved spectral diffusion, which arises from conformational fluctuations of the side groups attached to the MeLPPP backbone as well as of the surrounding host material. [source] Cationic Conjugated Polyelectrolytes with Molecular Spacers for Efficient Fluorescence Energy Transfer to Dye-Labeled DNA,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2007Y. Woo Abstract Two water-soluble conjugated polyelectrolytes, poly(9,9,-bis(6- N,N,N -trimethylammoniumhexyl)fluorene- alt -1,4-(2,5-bis(6- N,N,N -trimethylammoniumhexyloxy))phenylene) tetrabromide (P1i) and poly((10,10,-bis(6- N,N,N -trimethylammoniumhexyl)-10H-spiro(anthracene-9,9,-fluorene))- alt -1,4-(2,5-bis(6- N,N,N -trimethylammoniumhexyloxy))phenylene) tetrabromide (P2i) are synthesized, characterized, and used in fluorescence resonance energy transfer (FRET) experiments with fluorescein-labeled single-stranded DNA (ssDNA-Fl). P1i and P2i have nearly identical ,-conjugated backbones, as determined by cyclic voltammetry and UV-vis spectroscopy. The main structural difference is the presence of an anthracenyl substituent, orthogonal to the main chain in each of the P2i repeat units, which increases the average interchain separation in aggregated phases. It is possible to observe emission from ssDNA-Fl via FRET upon excitation of P2i. Fluorescein is not emissive within the ssDNA-Fl/P1i electrostatic complex, suggesting Fl emission quenching through photoinduced charge transfer (PCT). We propose that the presence of the anthracenyl "molecular bumper" in P2i increases the distance between optical partners, which decreases PCT more acutely relative to FRET. [source] Conjugated polymers with tethered electron-accepting moieties as ambipolar materials for photovoltaicsPOLYMER INTERNATIONAL, Issue 8 2007Antonio Cravino Abstract Conjugated polymers are of increasing interest as semiconductors for soft (opto)electronic devices, including photovoltaic elements. A promising conversion of solar energy into electrical energy is possible with blends of soluble electron donor-type conjugated polymers and fullerenes as electron-acceptor, transporting component. This approach, called bulk-heterojunction, suggested the preparation of intrinsic ambipolar materials to control simultaneously the electronic and morphological properties. On these bases, the covalent grafting of acceptor moieties onto conjugated backbones seemed attractive for the preparation of intrinsically ambipolar polymeric materials (,double-cable' polymers) as an alternative to donor,acceptor composites. The design, characterisation and application of this novel class of polymers are reviewed taking into account the current understanding of organic photovoltaics. Copyright © 2007 Society of Chemical Industry [source] | |||||||||||||||||||||||||