Emitting comonomers

The first oxetane-functionalized emitter were pyrene derivatives (Fig. 9.19(b), [46]), however, with very limited performance in OLEDs. Later, a poly(pheny-lene-fluorene)-copolymer was reported, however, without any electroluminescence data (Fig. 9.19(c), [47]). The breakthrough came with a recent report on a crosslinkable class of state-of-the-art spirofluorenes (Fig. 9.19(a), [48, 49]). By incorporating a green- and red-emitting comonomer, it was possible to generate the three primary colors (RGB) necessary for color-display applications. More recent concepts use sterically hindered 9,9 -diarylfluorene blocks to link conjugated oligomers (Fig. 9.19(d), [50]). 

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). 

All the copolymers showed similar absorptions with Lmax at 470 nm, which was more intense for polymers with higher thiophene content. In contrast, their emission colors were progressively red shifted with increasing thiophene-based comonomer content. Copolymer 596a emitted bright red light (620 nm) with reasonably high photoluminescent quantum yields (34-69%). 

There are several properties of luminescent materials that need to be controlled in order to make efficient LEDs and lasers. The first is the colour of the emission, which is primarily determined by the energy difference (band-gap) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), but in the solid state is also affected by interactions between the molecules or polymer chains which can lead to red-shifts in the emission due to formation of aggregates. This can be controlled by manipulating both the polymer backbone and the substituents. Polyphenylenes are intrinsically blue-emitting materials with large HOMO-LUMO gaps, but as we will show, by copolymerisation with other materials it is possible to tune the emission colour across the entire visible spectrum. Even without the incorporation of comonomers it is possible to tune the... 

If a very low mole fraction of a red or orange-emitting chromophore is incorporated into a PDAF, then energy transfer is incomplete so that emission from both the fluorene and the comonomer is observed. By carefully balancing the amounts of emission form the fluorene and comonomer, white emission can be obtained. This approach has been used very successfully by Wang and coworkers to obtain white-emitting copolymers [55]. The highest efficiency for white emission (9 cd/A), was obtained from copolymer... 

Scheme 13) containing 0.03 mol % of an orange emitting heterocyclic comonomer. Incorporation of low concentrations of green and red-emitting silole comonomers into a PDAF has also been used to obtain pure white emission [56]. 

Heeger and coworkers adopted bithiophene as comonomer to copolymerize with fluorene and found that the EL emission can be tuned to emit green light with a peak at 493 nm and a shoulder at 515 nm [57]. The HOMO and LUMO energy levels of copolymer 26 are 5.30 and 2.85 eV, respectively, as estimated... 

Dow Chemical Company presented a series of PF copolymers, consisting of various charge-transport moieties and low band-gap chromophores on the backbone, for tuning the emission color of PLED to cover the whole visible range [63]. They claimed that their blue-, green-, and red-emitting copolymers (without disclosing chemical structures and ratios of comonomers) can exhibit acceptable device performance, as shown in Table 1. 

Multilayer green light-emitting devices have been fabricated from poly(V-vinylcarbazole) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole. The EL is highly dependent on the thickness of the PPV layer in such devices. The performance is strongly dependent on the polymeric structure, which can be tuned by the introduction of side groups and comonomers. In polymers with bulky side groups, the intermolecular interactions are reduced. This effects an increased performance. ... 

Hazardous Decomp. Prods. Heated to decomp., emits acrid smoke and irritating fumes NFPA Health 1, Flammability 2, Reactivity 0 Uses Synthetic flavoring agent, fragrance in foods, candy, puddings, pharmaceuticals emollient in cosmetics comonomer for unsat. polyester resins (surface coatings)... 

Toxicology LC50 (inh., mouse, 4 h) 400 mg/m poison by inh. TSCA listed Hazardous Decomp. Prods. Heated to decomp., emits toxic vapors of NOx Uses Epoxy curing agent amorphous polyamide comonomer Manuf./Distrib. Air Prods. http //www.airproducts.com, Aldrich http //www.sigma-aldrich.com, BASF http //www.basf.com-, Fluka http //www.sigma-aidrich.com... 

Formuia CH2=C(CH3)COOCH2CH2NHC(CH3)3 Properties Liq. soi. 18g/i in water m.w. 185.27 dens. 0.914 (25 C) f.p. < -70 C b.p. 100-105 C (12 mm) flash pt. (COC) 96.1 C Toxicoiogy LD50 (IV, mouse) 174 mg/kg severe skin and eye irritant harmful if swallowed poison by IP route TSCA listed Precaution Combustible reactive monomer Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of NOx Uses Automotive dip tanks coating applies. industrial/consumer adhesives dye and lube oil additives intermediate for water treatment chemicals textile chemicals dispersant antistat stabilizer ion-exchange resins emulsifier precipitant acrylic resin comonomer food pkg. 

Properties Wh. gran, to pale yel. cryst. powd. sol. in water si. sol. in alcohol, acetone m.w. 180.17 dens. 1.25 dec. without melting 197-199 C Toxicology LD50 (oral, mouse) 350 mg/kg LDLo (subcut., rabbit) 500 mg/kg toxic by ing. mod. toxic by subcut. route TSCA listed Precaution Combustible Hazardous Decomp. Prods. Heated to decomp., emits toxic vapors of NOx Uses Comonomer for melamine-formaldehyde resins buffer, skin conditioner in cosmetics softener, antistat for hair care aikaii org. intermediate soaps component for fiame retardants... 

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