Due to their generally poor film-forming properties, small molecule-based organic semiconducting materials are mostly processed by vacuum deposition techniques to build up high performance „multi-layer“ devices. Nonetheless, a procession of these materials by low cost solution-based methods like inkjet-printing, spincoating or dipcoating is highly wanted. To build small molecule-based “multi-layer” architectures which are cast from solution, there are two main issues to overcome: 1) The formation of homogenous films and 2) the deposition of high-quality films of each layer, which must not be affected by the deposition of a subsequent layer. One way to meet these requirements and to build “multi-layered” devices from solution is the use of crosslinkable moieties which allow to form insoluble films before depositing additional layers. In this respect, the use of oxetanes which can be crosslinked through photoinitiated cationic ring-opening polymerization (CROP)[1] without affecting the optoelectronic properties of the semiconductor is of great interest. Up to now, their use as crosslinking units has been impressively demonstrated in the field of hole-transport and triplett-emitting materials.[2-4] To investigate new solution-processable materials, the motif of 6,12-dihydroindeno[1,2-b]fluorenes is of great potential. Indenofluorenes are known to be highly efficient blue emitting materials and their tetra-alkylated, as well as tetra-arylated derivatives are widely spread amongst both, polymeric and small molecule-based organic semiconducting materials.[5-7] However due to synthetic complexity, mixed substituted (pairwise alkylated and arylated) indenofluorenes (MIFs) are still rare in scientific literature.[8] In this work, we present the modular design synthesis, characterization and the solution based processing of a series of aryl-amine substituted, crosslinkable MIFs as small molecules for the potential application in multi-layered semiconducting devices. The compounds of this series synthesized by us bear various amounts of crosslinkable oxetane moieties per molecule, each of which is attached to the aromatic scaffold by alkylspacers of variable length. The crosslinkable units are located in either a geminal (molecule centered) or in a lateral fashion. The influence of the different substitution patterns on the molecular and film-forming properties, as well as on the crosslinking behavior is investigated. The studies are supported by DFT-calculations, CV- and UV/vis-measurements.
[1] J.-P. Fouassier, Photoinitiation, Photopolymerization and Photocuring: Fundamentals and Applications, 1 ed., Hanser, München, 1995. [2] M. S. Bayerl, T. Braig, O. Nuyken, D. C. Müller, M. Groß, K. Meerholz, Macromolecular Rapid Communications 1999, 20, 224-228. [3] G. Liaptsis, K. Meerholz, Advanced Functional Materials 2013, 23, 359-365. [4] G. Liaptsis, D. Hertel, K. Meerholz, Angewandte Chemie International Edition 2013, 52, 9563-9567. [5] S. Setayesh, D. Marsitzky, K. Müllen, Macromolecules 2000, 33, 2016-2020. [6] J. Jacob, J. Zhang, A. C. Grimsdale, K. Müllen, M. Gaal, E. J. W. List, Macromolecules 2003, 36, 8240-8245. [7] D. Thirion, J. l. Rault-Berthelot, L. Vignau, C. Poriel, Organic Letters 2011, 13, 4418-4421. [8] H. Kim, N. Schulte, G. Zhou, K. Müllen, F. Laquai, Advanced Materials 2011, 23, 894-897.