Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

PPV Copolymers

PPV and its alkoxy derivatives are p-type conductors and, as a consequence, hole injection is more facile than electron injection in these materials. Efficient injection of both types of charge is a prerequisite for efficient LED operation. One approach to lowering the barrier for electron injection is the use of a low work function metal such as calcium. Encapsulation is necessary in this instance, however, as calcium is degraded by oxygen and moisture. An alternative approach is to match the LUMO of the polymer to the work function of the cathode. The use of copolymers may serve to redress this issue. [Pg.11]

The composition of the copolymer determines its electroluminescence efficiency. Optimal efficiency (0.3%) was achieved in system 34 when the feed ratio of monomer 4 to monomer 34 was 9 1. This represents a 30-fold improvement in luminescence efficiency relative to PPV in the same device configuration (AlAEOs/polymer/Al) [58, 62]. Copolymer 33 has found uses as waveguides and [Pg.11]

The efficiency of PPV may also be raised by introducing disorder into the polymer chains. The crystallinity of PPV may be lowered by employing a modified Wessling method utilizing a xanthate leaving group [63]. PPV produced by this method is believed to contain a mixture of cis- and irani -alkene units. The efficiency of the material is 0.22% when employed in a single layer device with [Pg.12]


Substituted soluble PPV derivatives may also be synthesized by step-growth polymerization methods. Arylene-fc/.v-phosphylidenes may be condensed with ler-ephthaldehydes in a Wittig fashion to yield alternating PPV copolymers [52]. An alkoxy-substituted PPV derivative 28 (Scheme 1-8) prepared in this fashion emits in the orange (2nmx=585 nm) region of the spectrum [52]. [Pg.18]

Poly(l,4-phenylene vinylcne) and its Derivatives 2 The Basic Polymer LED Device Architecture 4 Substituted Poly(phcnylene vinylcne)s 6 Poly(anthrylenevinylcne)s 10 Step-Growth Routes to PPV Derivatives 10 PPV Copolymers 11... [Pg.321]

Electrical measurements on devices with different layer thickness have shown that the diode current depends on the applied field rather than the drive voltage. This is similar to what has been observed with our alternating PPV copolymers [68]. It indicates that field-driven injection determines the electrical characteristics. From Figure 16-39 it is evident that U-OPV5 has the lowest onset for both current and emission. By means of Fowler-Nordhcini analysis of the /-V -charac-teristics and optical absorption measurements, wc estimated the injection barrier for holes and the HOMO-LUMO gap, respectively [119]. The results of... [Pg.624]

Wittig or Wittig-Horner condensation between substituted terephthalaldehydes and p-xylene-diylphosphonium salts is also extensively used in the preparation of alternating PPV copolymers, e.g., containing different substituents in adjacent phenylene units (Scheme 2.8) [48]. [Pg.57]

SCHEME 2.15 Dependence of the electroluminescence of alkoxyphenyl-PPV copolymers on the comonomers ratio (PLED configuration ITO/PEDOT or PANI/polymer/Ca or Yb/Ag). [Pg.75]

SCHEME 2.17 Tuning the emission maxima in random phenyl-PPV copolymers. [Pg.76]

The diphenylamino-substituted PPV107, with solubilizing alkoxy groups, was synthesized by Shi and Zheng [150] via Wittig-Horner reaction (Chart 2.23). Its PL (555 nm) is very similar to that of diamino-PPV 64 and dialkoxy-PPV 14 homopolymers. The PLQY is rather high in solution (80%), but it drops to only 8% in films. Consequently, only a moderate EL efficiency of 0.6cd/A was obtained with this material (device ITO/PEDOT/107/Mg/Al) [150]. Almost simultaneously, Kido and coworkers [151] reported a similar diphenylamino-substituted PPV copolymer 108, which affords very efficient PLEDs. The device ITO/PEDOT/108/Ca/Al... [Pg.80]

The 2,5-dicyanophenylene unit has also been used by Jen and coworkers [164] in the synthesis of a series of polyfluorene (PF) PPV copolymers 129-131 through Suzuki-coupling... [Pg.83]

Neumann and coworkers [165] synthesized tetrafluorinated-PPV copolymer 133 and studied its light-emitting properties. However, this material was quite unsuccessful for LED applications increasing the amount of fluorinated comonomer resulted in a dramatic decrease of the PLQY and the turn-on voltage of the devices was above 30 V (which could only be realized in ac mode due to device shorting). The quenching was less pronounced for an analogous copolymer with MEH-PPV (134), which showed an EL efficiency of up to 0.08 cd/A (in ITO/PEDOT/134/Ca diode) [166] (Chart 2.26). [Pg.84]

As we already mentioned, electron-transporting properties of PPV polymers can be adjusted by introduction of an oxadiazole moiety in the polymer structure. A variety of PPV copolymers... [Pg.84]

Most recently, Jenekhe and coworkers [174] synthesized PPV copolymers with quinoxa-line as pendants 144 and 145, as well as a part of the chain (not shown here). These polymers showed reductions with onsets of —1.70 and —1.75 V vs. saturated calomel electrode (SCE),... [Pg.85]

The emission wavelength of PF-PPV copolymer can be red-shifted and the band gap reduced by introducing alkoxy substituents, as demonstrated for compounds 344 [421], Consequently, the transport of both holes and electrons is facilitated and the PLED built in the configuration ITO/PEDOT/344/A1 produces an orange-red color (AEL = 574-592 nm) with a maximum brightness for 344b of 13 50 cd/m2 and a luminous efficiency of 0.51 cd/A, at a rather low turn-on voltage of 2.5 V (Chart 2.87.)... [Pg.172]

In Aldrich, the widest collection belongs to PPV derivatives, which includes dialkoxy-PPVs (e.g., MEH-PPV 13,14), phenyl-substituted PPV 43, meta-para-linked PPV copolymer 159, etc. Many monomer precursors for PPV synthesis by Gilch and Wittig procedure as well as the Wessling Zimmerman precursor 2 for unsubstituted PPV are also available. [Pg.259]

Substituted-PPVs and a number of PPV copolymers have been synthesized, illustrated in Scheme 46, using the Heck reaction shown above [178-180]. Of these polymers both the phenyl-substituted PPV and the biphenylene vinylenes are soluble in organic solvents while the methyl-, trifluoromethyl-, nitro- and fluoro-substituted analogs displayed poor solubility. [Pg.94]

Horner-Wadsworth-Emmons procedures are also commonplace in synthetic materials chemistry, recent examples including donor-acceptor substituted molecules with bicyclo-spacers, which require napthalene-, anthracene-, and pyrene-substituted phosphonates, (112), (113) and (114) respectively, well-defined, electroactive PPE/PPV copolymers through the condensation of dialdehydes and bisphosphonate (115), ° and triphenylamine-substituted PPV. ° ... [Pg.629]

Recent encouraging results have been reported by Carter et al., who have obtained room temperature lifetimes in excess of 7000 h for encapsulated ITO/PPV/Ca devices at current densities of 60 mA/cm2.37 The polymer used was the PPV copolymer shown in Fig. 5.23, where the conjugation is interrupted by nonconjugated a -acetyloxy-/ -xylylene units. The efficiency of these devices was typically 0.02 lm/W. Devices operating at 80° C had lifetimes in excess of 1100 h. Carter et al., also reported devices based on the same emissive polymer giving efficiencies between 0.5 and 2 lm/W. These devices used a layer of conducting polymer (polyethylenedioxythiophene/polystyrene sulfonate) between the ITO and the PPV, and a sputtered aluminum/lithium alloy as the cathode. The devices... [Pg.149]

FIGURE 5.23. PPV copolymer with high luminescence efficiency. [Pg.149]


See other pages where PPV Copolymers is mentioned: [Pg.19]    [Pg.335]    [Pg.74]    [Pg.74]    [Pg.74]    [Pg.75]    [Pg.75]    [Pg.81]    [Pg.81]    [Pg.81]    [Pg.82]    [Pg.83]    [Pg.87]    [Pg.90]    [Pg.90]    [Pg.90]    [Pg.93]    [Pg.93]    [Pg.97]    [Pg.98]    [Pg.171]    [Pg.249]    [Pg.278]    [Pg.236]    [Pg.237]    [Pg.32]    [Pg.11]    [Pg.12]   


SEARCH



Block copolymers of PPVs

Conjugated PPVs block copolymers

PPE-PPV copolymers

PPV

© 2024 chempedia.info