In the last decade, oligoacenes have attracted a great deal of interest due to their unique electronic properties. These fused systems typically show multiple fine structure in absorption spectra and exhibit high charge carrier mobilities due to a rigid, planar, and fully conjugated backbone. Never-theless, the accessibility to larger acenes like hexacene is restricted due to the upcoming instability with increasing number of fused rings.[1] In this respect, novel S,N-heteroacenes consisting of linearly fused thiophene and pyrrole rings are a new promising class of heteroacenes, which combine the high stability of oligothiophenes with the favorable properties of acenes. Recently, S,N-hetero¬pent¬acenes with efficiencies of up to 6.5% in vacuum-processed organic solar cells (OSC)[2] and S,N-hetero¬hexacenes with hole mobilities of up to 0.02 cm2 V-1 s-1 in organic field effect transistors (OFET) [3] were synthesized and characterized at our institute. In this work, synthesis, characterization, and photovoltaic properties of A-D-A fused S,N-hetero-hexacenes with different alkyl chains at the nitrogen atoms will be reported. The influence of the alkyl side chains on the optical, electrochemical, and thermal properties will be discussed in detail. X-ray structure analysis gives a better understanding of the molecular packing and intermolecular inter¬actions of the molecules. Device optimization of vacuum-processed bulk-heterojunction solar cells (BHJSC) based on dicyanovinylene (DCV)-substituted S,N-heterohexacenes as donors and fullerene C60 as acceptor resulted in power conversion efficiencies of up to 6.9%.
[1] J. E. Anthony, Angew. Chem. Int. Ed. 2008, 47, 452-483. [2] A. Mishra, D. Popovic, A. Vogt, H. Kast, T. Leitner, K. Walzer, M. Pfeiffer, E. Mena-Osteritz, P. Bäuerle , Adv. Mater. 2014, 26, 7217-7223. [3] C. Wetzel, A. Mishra, E. Mena-Osteritz, A. Liess, M. Stolte, F. Würthner,
P. Bäuerle, Org. Lett. 2014, 16 , 362-365.