Cedric Fischmeister

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.

μSR in polymers

μSR can be applied to the study of various dynamical processes in polymers. These processes may relate to carrier motion, as in studies of conducting polymers which make use of muon generated polarons to measure carrier diffusion rates. Alternatively the processes of interest may be related to the structural dynamics of the polymer, which can show dramatic changes around the glass transition temperature. We report here examples of the use of μSR to study the muon states and muon mobility in the polymers polyethylene and polytetrafluoroethylene, where coherent FμF precession signals have been observed. In the case of polystyrene, muon radical states formed on the phenyl ring have been used to make a detailed study of the dynamical freezing and onset of static disorder that accompanies the glass transition. Finally, we report a study of polaron diffusion in two polyphenylenevinylene conducting polymers.

Muon-spin relaxation study of anisotropic charge carrier motion in polyphenylene vinylene-based polymers

Muon-spin relaxation (μ SR) experiments on the conducting polymers poly(2, 3-dibutoxy-1, 4-phenylene vinylene) and poly(2, 5-bis(dimethyloctylsilyl)-1, 4-phenylene vinylene) probe the dynamics of the highly mobile polarons created by the muon-implantation process in which muonium reacts with the polymer forming a radical state. The fluctuating spin density induced by the electronic spin defect rapidly diffusing up and down the chain leads to a characteristic relaxation, the temperature and field dependences of which permit the extraction of intrachain and interchain diffusion rates. The intrachain diffusion rate decreases with temperature and can be fitted to a model of phonon-limited transport. The interchain diffusion rate increases with temperature and can be fitted to an activated temperature dependence.

Ortho-Metallation as a key step for the synthesis of silyl substituted Poly(p-phenylenevinylene)s

A new synthetic pathway for the preparation of silyl substituted poly(p-phenylenevinylene) (PPV) precursors has been investigated. By using directed ortho-metallation, it has been possible to significantly improve the overall yields for the synthesis of mono- and disubstituted silyl monomers. We have also synthesised a new unsymmetrically substituted monomer. From these monomers we have synthesised the following polymers: DMOS-PPV 1 (DiMethylOctlylSilyl-PPV), BDMOS-PPV 2 (Bis-(DiMethylOctlylSilyl)-PPV)), BDMDS-PPV 3 (Bis-(DiMethylDecyllSilyl))-PPV and C8C10-PPV (2-(dimethyloctylsilyl)-5-(dimethyldecylsilyl))-PPV 4.

New routes to monomers and polymers for LEDs

The synthesis of poly(1,4-phenylene vinylene)s (PPVs) containing a 2,3-dialkoxy substitution pattern has been developed. Poly[2,3-bis(2-ethylhexyloxy)-1,4-phenylene vinylene] (BEH-PPV) 4 was prepared by Gilch polycondensation, and its optical properties were compared with the recently discussed poly(2,3-dibutoxy-1,4-phenylene vinylene) (DB-PPV) 1. The precursors for the Gilch method have traditionally been prepared by methods which have certain disadvantages. These can be overcome by the use of directed metallation reactions which are illustrated in the synthesis of some poly(2,5-disilyl-substituted 1,4-arylene vinylene) derivatives.

Design of Luminescent Polymers for Leds

A 2,3-dibutoxy-1,4-phenylenevinylene comonomer was incorporated into a distyrylbenzene derivative 11. Novel 1,2-disubstituted-3,6-dibromobenzene comonomers 15 and 18 were prepared by directed metallation. Copolymerization of I I with a 9,9-dioctylfluorene-2,7-diboronate ester I yielded a green fluorescent polymer while copolymerization of 15 and 18 with the 9,9-dihexylfluorene-2,7-diboronate 22 afforded promising blue fluorescent polymers 23 and 24 respectively.

Synthesis of New Building Blocks for Light Emitting Polymers

The synthesis of poly(2,3-dibutoxy-1,4-phenylene vinylene) (DB-PPV) has allowed the study of this material as the active layer in a multiple layer device using a composite combination of polymer and Alq 3 with an oxadiazole as electron injection/transport layers. The luminous efficiency of the resulting device was significantly improved as a result of this combination of transport layers. An entirely new approach to the synthesis of monomers for PPV precursors is described in which the 2- and 5- substituents are introduced by directed metallation groups (DMGs) which ultimately become the bis(halomethyl) groups.