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Séminaire Chimie ED459

Dimensionality and alignment of organic semiconductors

Prof. Yves H. Geerts (Laboratoire de Chimie des Polymères, Université Libre de Bruxelles, Belgique)

publié le , mis à jour le

Le Jeudi 14 Mai 2009 à 14h
ENSCM, Amphithéâtre Gerhardt

The discovery that 2,3,6,7,10,11-hexahexylthiotriphenylene 1 exhibits a charge carrier mobility (µ) on the order of µ = 0.1 cm2.V–1s–1,[1] has created wide scientific and technological interests in discotic liquid crystals as potential candidates for optoelectronic applications.[2] Since then, µ of several mesogenes based on hexabenzocoronene, triphenylene, and phthalocyanine aromatic cores have been studied.[3] Values of µ as high as 0.5 cm2.V–1s–1 have been reported for the columnar mesophase of hexabenzocoronene derivatives.[4] Such mobility approaches the corresponding value for the intersheet µ in graphite (3 cm2.V–1s–1) and matches those of single crystals of aromatic compounds.[4] However, most of the discotic mesogenes reported so far have in common to be better hole carriers than electron carriers.[3] Only a few examples of electron carrier discotic mesogenes exist to date[5,6] creating, therefore, the need for new materials.

We will report the synthesis, mesophase characterisation and property investigation of new type of discotic molecules such as 2,3. The presence of six nitrogen atoms in the aromatic core is anticipated to significantly increase the first reduction potential facilitating electron injection and high electron mobility.[7] Surprisingly, it was discovered that the six nitrogen atoms caused a dramatic change in the mesomorphic behaviour.[8]. Whatever its side chains, compound 2 is not liquid crystalline whereas structurally related 1 and 3 exhibit one to several liquid crystalline phases. The occurrence of liquid crystalline mesophases appears for mesogen 4 when thioalkyl side chains are replaced by side chains connected by amide functions. An extremely short intracolumnar distance of 3.18 Å is observed for this compound that exhibit an unusually high charge carrier mobility.[9] This short distance is imposed by intermolecular Hydrogen bonding. Compound 4 can be viewed as a supramolecular polymer where repeating units are connected by non-covalent bonds. We will also report on highly fluorescent columnar mesophases and crystals. The concept of non-parallel transition dipoles has then be successfully extended to mesogen 6 that forms columnar hexagonal mesophases. A fluorescence quantum yield as high as φ = 0.6, i.e. superior to the values encountered for poly(fluorene)s and poly(p-phenylenevinylene)s commonly used in LED ![10]

Figure 1 (cliquer pour l’agrandir)

1. D. Adam et al., Nature 1994, 371, 141.
2. S. Sergeyev, W. Pisula, Y. H. Geerts, Chem. Soc. Rev. 2007, 1902-1929.
3. A. van de Craats et al., Adv. Mater. 2001, 13, 130.
4. A. van de Craats et al., Adv. Mater. 1998, 10, 36. A. van de Craats et al. Adv. Mater. 1999, 11, 1469.
5. C W. Struijk et al., J. Am. Chem. Soc. 2000, 122, 11057.
6. A. van de Craats, PhD. Dissertation, Delft University of Technology, June 2000.
7. F. Uckert et al. Adv. Mater. 2000, 12, 905.
8. O. Roussel et al., Molec. Cryst. Liq. Cryst. 2003, 396, 35-39.
9. R.I. Gearba et al., Adv. Mater. 2003, 15, 1614.
10. A. Hayer, V. de Halleux, A. Köhler, A. El-Garoughy, E. W. Meijer, J. Barberá, J. Tant, J. Levin, M. Lehmann, J. Gierschner, J. Cornil, Y. H. Geerts, J. Phys. Chem. B 2006, 110, 7653.


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