Para-phenylene vinylenes

The PL spectrum and onset of the absorption spectrum of poly(2,5-dioctyloxy-para-phenylene vinylene) (DOO-PPV) are shown in Figure 7-8b. The PL spectrum exhibits several phonon replica at 1.8, 1.98, and 2.15 eV. The PL spectrum is not corrected for the system spectral response or self-absorption. These corrections would affect the relative intensities of the peaks, but not their positions. The highest energy peak is taken as the zero-phonon (0-0) transition and the two lower peaks correspond to one- and two-phonon transitions (1-0 and 2-0, respectively). The 2-0 transition is significantly broader than the 0-0 transition. This could be explained by the existence of several unresolved phonon modes which couple to electronic transitions. In this section we concentrate on films and dilute solutions of DOO-PPV, though similar measurements have been carried out on MEH-PPV [23]. Fresh DOO-PPV thin films were cast from chloroform solutions of 5% molar concentration onto quartz substrates the films were kept under constant vacuum. 

Concerning the nature of electronic traps for this class of ladder polymers, we would like to recall the experimental facts. On comparing the results of LPPP to those of poly(para-phenylene vinylene) (PPV) [38] it must be noted that the appearance of the maximum current at 167 K, for heating rates between 0.06 K/s and 0.25 K/s, can be attributed to monomolecular kinetics with non-retrapping traps [26]. In PPV the density of trap states is evaluated on the basis of a multiple trapping model [38], leading to a trap density which is comparable to the density of monomer units and very low mobilities of 10-8 cm2 V-1 s l. These values for PPV have to be compared to trap densities of 0.0002 and 0.00003 traps per monomer unit in the LPPP. As a consequence of the low trap densities, high mobility values of 0.1 cm2 V-1 s-1 for the LPPPs are obtained [39]. 

Several attempts to use otganic polymeric semiconductors as the active component in photovoltaic devices have been reported during the last two decades. Interest in the photovoltaic properties of conjugated polymers like polyacelylcne, various derivatives of polythiophenes and poly(para-phenylene vinylene)s arose from... 

Two leading examples, that is, the preparation of high-quality graphene flakes by processing THF solutions of a zinc-based phathalocyanine (ZnPc) linked to an n-type oligo-para-phenylene-vinylene (oPPV) backbone of different chain lengths (Fig. 18.10), have been recently reported [121,122], More specifically, the authors estab-... 

Light-emitting polymers [46,48] are a more recent development and may eventually prove superior to small-molecule OLED. Typical polymers are the green poly(para-phenylene vinylene) (PPV 53), the orange-red dialkoxy derivatives (54), and the blue polyfluorene (55) [48],... 

O. Lhost and J. L. Bredas, ]. Phys. Chem., 96, 5279 (1992). Theoretical Study of Torsion Potentials in traws-Stilbene and Substituted truns-Stilbenes Modeling Torsions in Poly(para-phenylene vinylene) and Derivatives. 

FIGURE 1.2. Molecular structure of widely used it-conjugated and other polymers (a) poly(para-phenylene vinylene) (PPV) (b) a (solid line along backbone) and it ( clouds above and below the a line) electron probability densities in PPV (c) poly(2-methoxy-5-(2 -ethyl)-hexoxy-l,4-phenylene vinylene) (MEH-PPV) (d) polyaniline (PANI) (d.l) leucoemeraldine base (LEB), (d.2) emeraldine base (EB), (d.3) pernigraniline base (PNB) (e) poly(3,4-ethylene dioxy-2,4-thiophene)-polystyrene sulfonate (PEDOT-PSS) (f) poly(IV-vinyl carbazole) (PVK) (g) poly(methyl methacrylate) (PMMA) (h) methyl-bridged ladder-type poly(jf-phenylene) (m-LPPP) (i) poly(3-alkyl thiophenes) (P3ATs) (j) polyfluorenes (PFOs) (k) diphenyl-substituted frares -polyacetylenes (f-(CH)x) or poly (diphenyl acetylene) (PDPA). 

Processing through a precursor route involves the use of an intermediate, processible polymer that can be later converted into the fully conjugated material. It is most often used with poly(para-phenylene vinylene (PPV), a relatively stable and insoluble polymer that can be manipulated as soluble precursor polymers to form films and fibers. There are many different... 

Si-PPV Poly(dimethylsilylene-/7ora-phenylenevinylene-(2,5-di- -octyl-para-phenylene)-vinylene-... 

Figure 15-25. (a) The molecular structures of poly(2,5-dioctyloxy-para-phenylene vinylene) (OOPPV) and octaethylporphine (OEP) and the structure of the three layer photocell, (b) Schematic energy band diagram of the three layer photocell (reproduced by permission of the Japanese Physical Society from Ref. [94]). 

DHPPV poly(2,5-diheptyl-para-phenylene vinylene)... 

Poly(arylene vinyene)s (PAVs) represent the most widely studied group of electroluminescent polymers. The parent compound poly(para-phenylene vinylene) (PPV, 1, Fig. 6.1) [5] is insoluble and so must be processed as a precursor polymer but derivatives such as MEH-PPV (2) [6] with solubilizing alkyl, aryl, silyl, or al-koxy chains show good solubility in organic solvents and so can be readily processed by techniques such as spin casting. By appropriate choice of substituents... 

FIGURE 8.9 Linear unsubstituted conjugated polymers poly(p-phenylene), poly(para-phenylene vinylene), polythiophenes, and polyfluorenes. 

Poly(para-phenylene vinylene)s from green to red light-emitting materials... 

Synthesis Poly(para-phenylene vinylene) (PPV, XI) is the archetypical fluorescent polymer. It emits a bright green-yellow light with two emission peaks at 520 nm (2.38 eV) and 550 nm (2.25 eV). Direct synthesis of XI yields an intractable,... 

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