Beng Sim Chuah

Light-emitting devices based on a poly(p-phenylene vinylene) derivative with ion-coordinating side groups

We report the phase-separation and the optoelectronic properties of an alternating poly(p-phenylene vinylene)-based copolymer, to which poly(ethylene oxide), PEO, and or lithium triflate are added. The alternating units of this copolymer (DB-BTEM-PPV) are 2,3-dibutoxy-1,4-phenylene vinylene, and 2,5-bis(triethoxymethoxy)-1,4-phenylene vinylene, a moiety containing side groups allowing ion solvation and transport. Upon addition of the ion-transporting polymer PEO to DB-BTEM-PPV blended with lithium triflate, we have found a sizeable efficiency increase (from 0.9 to 1.5 cd/A), with a concomitant increase of the response time. We propose that this is due to solvation and complexation of lithium triflate by the PEO, which simultaneously reduces the quenching of photoluminescence (and electroluminescence) efficiency by the ionic charge, and the effectiveness of formation of highly doped, low-barrier, polymer/electrode interfaces. We discuss charge transport and injection in the copolymer and in the blend with ...

New luminescent polymers for LEDs

Abstract Recent results are reported on the synthesis of statistical copolymers 8 and 9 derived from the highly luminescent silyl PPV derivative (DMOS-PPV) with various alternative building blocks carrying side chains capable of supporting polyelectrolytes. These polymers are prepared by Gilch dehydrohalogenation polymerization. It is of interest to study the effect on charge transport in standard electroluminescent (EL) devices using these PPV copolymers. Moderately efficient conventional single-layer devices are obtained for copolymer 9 . When fabricated in a light-emitting electrochemical cell (LEC) configuration (lithium triflate) without any extra supporting polymer electrolyte (e.g., poly(ethylene oxide), PEO), devices based on both 8 and 9 show lower turn-on voltages and improved efficiency.

Light-emitting electrochemical cells based on poly(p-phenylene vinylene) copolymers with ion-transporting side groups

We present the electro-optical characteristics of LECs based on two copolymers derived from poly(p-phenylene vinylene), DB-alt-BTEM-PPV and BDMOS-co-BTEM-PPV, having ion-transporting side groups. We find typical LEC behaviour upon addition of lithium triflate. Addition of poly(ethylene oxide), PEO, improves the EL efficiency, but the response time increases. We discuss these observations on the basis of PEO-induced phase separation.

A green emitting, alkoxy disubstituted poly(p-phenylene vinylene) for Electroluminescent Devices

Abstract We report the effects of the substitution of butoxy chains on the phenyl 2,3 positions of poly(p-phenylene vinylene) (PPV). We find that this substitution has a remarkable influence on the optical and electroluminescent properties of the resulting semiconductor (DB-PPV) which does not show the red-shift of the emission, typical of alkoxy substituted PPVs, such as poly(2-methoxy-5-(2′-ethyl-hexyloxy)-l, 4-phenylene vinylene), MEH-PPV, dominated by the influence of the π-electron rich oxygen atom. We report photoluminescence (PL), quantum efficiencies of 40%, electroluminescence (EL) efficiencies of 0.6 cd/A in 2-layer ITO/PPV/DB-PPV/Ca diodes, and luminances up to 4500 cd/m 2 .

Versatile synthesis of various conjugated aromatic homo- and copolymers

In recent years, variously substituted derivatives of poly(1,4-phenylene vinylene)s have emerged as efficient candidates for the emissive layer in polymer light emitting diodes. The synthetic routes for these polymers divide between precursor routes and those leading to fully conjugated solvent-processible polymers. The Gilch dehydrohalogenation polycondensation has largely been used for the latter class. In this presentation, we describe a novel family of 2,3-disubstituted aromatic precursors, derived from catechol, and we report their efficient polymerisation as homo- and copolymers with, for example, silyl-substituted derivatives to give materials which are highly fluorescent and serve as interesting materials in polymer LEDs.

Luminescence properties of PPV-based copolymers with crown ether substituents

We present the optical properties of four poly(p-phenylenevinylene) (PPV)-based statistical copolymers, which combine monomers of highly luminescent polymers and monomers carrying crown ether side groups. The photoluminescence efficiency for films on spectrosil ranges from 28% to 52%, whereas the electroluminescence (EL) efficiency of single-layer diodes with Al cathodes reaches 0.6 cd/A (internal quantum efficiency of 1.4%). Surprisingly, the efficiency for Ca cathodes diodes is lower than for Al ones. Slight variation of the EL spectra from pixel to pixel affects all the copolymers of the family, and we consider that it is indicative of chain aggregation induced by the crown ether moieties. Studies of light-emitting electrochemical cells, LECs, based on one of these polymers show that the ion mobility induced by the presence of the crown ethers is relatively small. Typical LEC behaviour was observed upon addition of poly(ethylene oxide), with EL internal quantum efficiency reaching 2.3%.

Novel luminescent polymers

Abstract We report the synthesis and luminescence properties of poly[2,5-bis(dimethyloctylsilyl)-l,4-phenylene vinylene)](BDMOS-PPV) 4 and its statistical copolymer poly[2,5-bis(dimethyloctylsilyl)-1,4-phenylene vinylene)]-co-[2,5-bis(trisethoxymethoxy)-1,4-phenylene vinylene)] (BDMOS-BTEM-PPV) 6 with units carrying ion-transporting triethoxy side-chains. The highly fluorescent polymers were synthesised by dehydrohalogenation polymerisation and show promise as materials for LED and LEC fabrication.

A highly luminescent polymer for LEDs

Abstract A new 2,3-dibutoxy-l,4-phenylene vinylene is reported with high photoluminescence (40%) and electroluminescence efficiencies. The unusual substitution pattern is effective in tuning the emission colour as the polymer exhibits unexpected blueshifted emission to the green region. Crystal structures of model oligomers (PL efficiencies 80%) and theoretical calculations on optimised geometry offer insight into these interesting properties.

Efficient electroluminescent poly(p-phenylene vinylene) copolymers for application in LEDs

A new and efficient route for the synthesis of poly(p-phenylene vinylene)s (PPVs) containing dialkoxy substituents at the 2,3-positions of the phenylene ring of the polymer backbone has been developed. In comparison to the more classical 2,5-substitution pattern these PPV polymers show a significantly blue-shifted longest-wavelength absorption (lambda (max)) and emisson band (lambda (em)). Two statistical PPV copolymers comprising 2,3-dibutoxy and dimethyloctylsilyl- or 2,5-bis(dimethyloctylsilyl) side-chains were synthesized via the Gilch dehydrohalogenation route. Double-layer light-emitting devices (LEDs) of the configuration ITO/PEDOT/polymer/Ca were demonstrated to combine high electroluminescence efficiencies with low turn-on voltages.

New Luminescent PPV Derivatives for Led Applications

A new poly(phenylenevinylene) [PPV] derivative 8 with dialkoxy substituents at the 2,3- positions of the phenylene ring of the polymer backbone has been prepared. This exhibited significantly different properties compared with the typical 2,5-dialkoxy substituted PPV derivatives. The polymer is not only significantly blue-shifted in its optical and luminescence properties but also has high photoluminescence (PL) and electroluminescence (EL) efficiencies. Investigation of the model oligomer 11 offers insight into this interesting behavior.