Research AK Bunz: Large Heteroacenes

Pentacene and TIPS-pentacene are nowadays reference materials for thin-film transistors (OFETs) exhibiting excellent hole mobilities but poor electron transport characteristics. Introduction of electronegative atoms directly into the perimeter of the acenes preserves brick-wall-like packing for TIPS-tetraazapentacene (TIPS-TAP) with electron mobilities up to 3.3 cm2V-1s-1.
 
Strukturzeichnung Synthese eines TIPS-Tetraazapentacen-Derivates
 
In order to obtain tetraazapentacenes employing classic condensation reactions, an efficient reduction protocol to the so far elusive bisalkynylated 3,6-diiminocyclohexa-1,4-diene-1,4-diamine has been developed. This building block accesses novel derivatives in a one-step condensation reaction with ortho-quinones.
 
Strukturzeichnung Synthese von bisalkynyliertem 3,6-Diiminocyclohexa-1,4-diene-1,4-diamin
 
Synthesis of TAP-derivatives may also proceed via addition-elimination routes. Extension of this concept by coupling to larger fluorinated arenes results in dimerization after oxidation.
 
Strukturzeichnung Synthese von TAP-Derivativen via Addition/Eliminierung
 
These established classic methods employing harsh conditions can fail in the synthesis of substituted azaacenes. However, development of Pd-catalyzed coupling reactions allows the coupling of activated halides as well as in some cases of deactivated halides to yield a variety of azahexacenes.
 
Strukturzeichnung Synthese von Azahexazenen mittels PD-katalysierter Kupplungsreaktion
 
With our expertise in Pd-catalyzed coupling, synthesis of diazahexacenes and diazaheptacenes was carried out. The formed N,N’-dihydrodiazaheptacenes were easily oxidized to give the corresponding heptacenes in less than one minute. The depictured azaheptacene is reasonably stable and persists in solution, whereas smaller silyl substituents do not inhibit dimerization as efficiently as sec-butyl groups.
 
NMR-Diagramme + Strukturzeichnung Dimerisation von Diazaheptacenen
 
Research in the Bunz group is not only limited to organic synthesis but also focuses on processing of our semiconducting molecules in devices (OFETs, OLEDs). Zone-casting of TIPS-TAP on polyimide substrates, which shows ideal wettability for easy fabrication, produced uniaxially oriented crystallites, giving mobilities of up to 0.42 cm2V-1s-1 in BG/TC OFETs.
 
Bild Halbleiterentwicklung mit TIPS-TAP auf Polyimid-Substrat + Foto Kristallphasen
 
Selected References
 
Miao, S.; Appleton, A. L.; Berger, N.; Barlow, S.; Marder, S. R.; Hardcastle, K. I.; Bunz, U. H. F.:
"6,13-Diethynyl-5,7,12,14-tetraazapentacene".
Chem. Eur. J. 2009, 15, 4990-4993.
 
P. Biegger, M. Schaffroth, K. Broedner, O. Tverskoy, F. Rominger, U. H. F. Bunz:
"A bisalkynylated 3,6-diiminocyclohexa-1,4-diene-1,4-diamine".
Chem. Comm. 2015, 51, 14844-14847.
 
J. U. Engelhart, B. D. Lindner, O. Tverskoy, F. Rominger, U. H. F. Bunz:
"Partially Fluorinated Tetraazaacenes by Nucleophilic Aromatic Substitution".
J. Org. Chem. 2013, 78, 10832-10839.
 
B. D. Lindner, J. U. Engelhart, O. Tverskoy, A. L. Appleton, F. Rominger, A. Peters, H.-J. Himmel, U. H. F. Bunz:
"Stable Hexacenes through Nitrogen Substitution".
Angew. Chem. Int. Ed. 2011, 50, 8588-8591.
 
J. U. Engelhart, B. D. Lindner, M. Schaffroth, D. Schrempp, O. Tverskoy, U. H. Bunz:
"Substituted Tetraaza- and Hexaazahexacenes and Their N,N'-Dihydro-Derivatives. Syntheses, Properties and Structures"
Chem. Eur. J. 2015, 21, 8121-8129.
 
J. U. Engelhart, O. Tverskoy, U. H. F. Bunz:
"A Persistent Diazaheptacene-Derivative".
J. Am. Chem. Soc. 2014, 136, 15166-15169.
 
F. Paulus, J. Engelhart, P. Hopkinson, C. Schimpf, A. Leineweber, H. Sirringhaus, Y. Vaynzof, U. H. F. Bunz:
"The Effect of Tuning the Microstructure of TIPS-Tetraazapentacene on the Performance of Solution Processed Thin Film Transistors".
J. Mater. Chem. C 2016, 4, 1194-1200.
 
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Letzte Änderung: 29.08.2017
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