Preparation of highly pure quaterthiophene and role of impurities on its photoluminescence properties

Journal of Materials Chemistry

Volumn 14, Issue 2, 2004, Pages 171-178

  Trabattoni, Silvia ^a   Laera, Stefano ^a   Mena, Renzo ^b   Papagni, Antonio ^a   Sassella, Adele ^a  

^a UNIVERSITY OF MILANO BICOCCA   (Italy)

^b NiKem Research   (Italy)

Author keywords

[No Author keywords available]

Indexed keywords

CONTAMINATION; GAS CHROMATOGRAPHY; MASS SPECTROMETRY; PHOTOLUMINESCENCE; THIN FILMS;

COUPLING REACTIONS;

AROMATIC COMPOUNDS;

ORGANOMETALLIC COMPOUND; THIOPHENE DERIVATIVE;

ARTICLE; CHEMICAL STRUCTURE; CONTAMINATION; FILM; GAS CHROMATOGRAPHY; MASS SPECTROMETRY; PHOTOLUMINESCENCE; SYNTHESIS; TEMPERATURE;

EID: 0942268757     PISSN: 09599428     EISSN: None     Source Type: Journal    
DOI: 10.1039/b309150c     Document Type: Article

References (34)

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9. Distillation under reduced pressure is exploitable only on large quantities of material since it requires a fractional column of suitable length to separate Br-2T from starting 2T of similar boiling point. Crystallization from methanol, as described, is useful for purifying Br-2T contaminated by small amounts of 2Br-2T derivatives but is ineffective on the crude bromination mixture.
10. f (2Br-2T) = 0.68.
11. f factor: 0.35 for 2Br-2T, 0.55 for Br-2T and 0.70 for 2T. It is of note that the observed elution order of 2T, Br-2T and 2Br-2T is, in this phase, opposite to that observed in the direct phase. This difference can be ascribed to a major polarity of the α-C-H thiophene bonds with respect to α-C-Br thiophene which results in minor interaction of the 2T with the RP18 silica gel relative to Br-2T or 2Br-2T when compared with that possible with the direct phase (probably hydrogen bonding is involved).
12. In order to avoid any contamination of Br-2T by C18-silanols detached from the surface, before each Chromatographic purification, the adsorbent has to be conditioned eluting first with methylene chloride, then with hexane and finally with acetonitrile.
13. The acetonitrile collected from the fraction containing Br-2T and 2Br-2T can be directly recycled without any problems. Due to the appreciable vapour pressure of 2T, the recovered acetonitrile is contaminated and hence is not recyclable.
14. The reported reaction procedure was modified as follows: after quenching the reaction with water, the brown solid that precipitated was collected by filtration, then dissolved in methylene chloride and the solution filtered through a silica gel plug. This removes the major part of metal-containing by-products. After removing the solvent, the obtained dark brown solid material was taken up with hexane leaving a bronze-brownish solid.
15. TLC performed on silica gel with hexane-methylene chloride (9:1) eluent shows only the characteristic light blue fluorescent spot of 4T.
16. Under this lamp usually the fluorescence of unsat urated molecules are detected. Since fluorescence is 10-1000 times more sensitive (depending on the nature of molecule) than absorption, the use of this lamp further improved the detection limit of TLC.
17. Sometimes there is another fluorescence spot (B): in these cases spot C is absent.
18. Due to the low solubility of 4T in the mobile phase, the RTLC should not be overcharged in order to avoid elongated 4T spots that cover those of impurities.
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22. 4T was used as a sample for DSC stability tests and shows a very sharp melting point at 214.2°C. No changes in the melting point were observed even after 12 melting-solidification cycles.
23. The purity of 4T was periodically checked during the sublimation by RTLC. Sometimes, the first collected material (few% of the total) was found to be contaminated from impurity B. The presence of contaminant(s) rapidly fades with time during the sublimation. This may be due to the contaminant(s) having a similar vapour pressure as 4T; sublimation concentrates them in the first collected material making their fluorescence still visible by RTLC.
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25. This trend has some analogies with the analysis of 2T, Br-2T and 2Br-2T on reverse phase thin layer chromatography.
26. 6T is, on request, available from Organics Inc. Woburn, MA 01801.
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30. No mention of this type of insertion is reported in a recent review: J. Hassan, M. Svignon, C. Gozzi, E. Schulz and M. Lemaire, Chem. Rev., 2002, 102, 1539-1469. Indeed a similar C-P breaking in phosphine ligands has been recently observed in palladium catalysed cross coupling reactions: G. Mann, C. Incarvito, A. L. Rheingold and J. F. Hartwig, J. Am. Chem. Soc., 1999, 121, 3224-3225.
31. No mention of this type of insertion is reported in a recent review: J. Hassan, M. Svignon, C. Gozzi, E. Schulz and M. Lemaire, Chem. Rev., 2002, 102, 1539-1469. Indeed a similar C-P breaking in phosphine ligands has been recently observed in palladium catalysed cross coupling reactions: G. Mann, C. Incarvito, A. L. Rheingold and J. F. Hartwig, J. Am. Chem. Soc., 1999, 121, 3224-3225.
32. The reaction was repeated three times with yields ranging from 80 to 90%.
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