Polyfluorene (PF) and its derivates as well-known fluorescent materials are promising materials in optoelectronic applications due to their high quantum yields in the solid state. Nevertheless, the easy chain inter-action in PFs to result in the unfavorable associations (aggregate and excimer) are generally considered to be detrimental to the emission efficiency in the concentrated solid state and/or at high temperatures. In the study, restraining the extent of associations is therefore by embedding fluorene-based alternative and block copolymers in crosslinked network as matrix.
Firstly, alternative copolymers with fluorene connected by anthracene (or pyridine or fluorene) ring were prepared through Suzuki coupling. In this way, the steric hindrance between the o-hydrogens in the neighboring aromatic ring causes the twisting of the constructed polymer chain and the resulting twisting chain conformation keeps the polymer chains from the unfavorable inter-chain interactions and reduces the extent of the association. Secondly, the alternative fluorene-anthracene copolymer (a-PFA) from the first approach can be further chemically formulated to obtain a triblock copolymer with the central a-PFA rod block connected by two flexible poly(methyl methacrylate) (PMMA) segments. In this way, the two flexible PMMA chains serve as spatial isolator to keep the central PFA rod from approaching each other and a reduced extent of association is expected for this block polymer of b-PMMA-PFA. Thirdly, all the alternative and block copolymers cited above were immersed in the curable liquid methyl metharcylate (MMA)/ditrimethylolproanetetracrylate (DTTPT) monomer mixtures and photo-irradiated to obtain composites with the fluorescent polymers immersed in the cured crosslinked network. The chain morphology and thus the degree of associations will be successfully frozen by the immobilized crosslinked network.
For systems before and after photo-irradiation, the degree of aggregation was evaluated by Uv-vis absorption, photoluminescent (PL) and PL excitation spectroscopy. Polymer concentration was found to be important factor in controlling the degree of aggregation and was discussed in this study. In addition, the cured solid composites after high-temperature annealing were studied and compared with pure PFs to evaluate the effectiveness of this crosslinking strategy in restraining the extent of aggregation. In most cases, quantum yields (£XPLs) also were measured to evaluate the effectiveness of this strategy.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0109107-200348 |
| Date | 09 January 2007 |
| Creators | Su, Fu-Kun |
| Contributors | R. M. Ho, Yun Chen, T. H. Chang, L. C. Liang, C. L. Chen, L. L. Lin, J. L. Hong |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0109107-200348 |
| Rights | not_available, Copyright information available at source archive |
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