Functionalization of BN-Pyrenes/Phenanthrenes andIncorporation into Organic Materials
Final Report Abstract
Polycyclic aromatic hydrocarbons (PAHs), particularly acenes, have garnered considerable interest due to their potential as organic semiconducting materials. These fused aromatic compounds have been used to fabricate electronic transistor and light-emitting diode devices. The accessibility of higher acenes is limited due to their reduced light and oxygen stability and their low solubility. However, their remarkable properties are motivation for the development of methods for more efficient and scalable syntheses, the connection of PAH units and the preparation of compounds with more extended conjugation. This project was focused on boron/nitrogen-containing PAH-materials. The transposition of carbon-carbon units for the isoelectronic boron-nitrogen (BN) elements in the all-carbon frameworks is thought to introduce new, appealing properties without disturbing the electronic structure significantly. First attempts were made on functionalizing the known BN-pyrenes for subsequent connection for instance by coupling reactions. This pathway which turned out not to be successful would have given access to polymers of BN-containing PAHs. The attention was then directed to the preparation of extended BN-π-systems (BN-acenes). We were able to synthesize a novel class of BN-containing polyaromatic hydrocarbons – BN-dibenzo[a,o]picenes (BN-DBPs). These compounds can serve as a synthetic alternative to their hitherto unknown all-carbon analogs. The structural properties of these compounds were fully investigated using various experimental methods. As expected these systems are not planar, but interestingly inhabit a di-helical structure. The BN-DBPs show significant πstacking in the solid state, which might utilize these compounds for application in organoelectronics. Due to the incorporated BN-units they furthermore show pronounced photophysical properties such as strong fluorescence. Cyclic voltammetry measurements point to a good electrochemical stability and suggest a possible application as OLEDs (organic light emitting diodes) or OFET (organic field effect transistors). Computational chemistry gave further insight into the electronic structure and the photophysical processes involved. More importantly, the BN-DBPs were found to be only slightly oxygen sensitive and completely stable towards coordinating agents and even water. Furthermore, they show high thermal and photo stability. Following the route of BN-containing PAHs we were also able to synthesize a number of BN-[4]-helicenes. Here the synthetic route is – similar to the synthesis of the BN-DBPs - simplified due to the formation of BN bonds. Helicenes are of general interest because of their photophysical and electronic properties. We were able to fully characterize these novel BN-helicenes and investigate their absorption and emission properties. Furthermore, our work shows that even higher helicenes such as BN-[5]-helicenes are accessible. In conclusion we report on novel π-extended BN-containing polyaromatic hydrocarbons with remarkable properties. Furthermore, the synthetic pathways used provide the basis for the preparation of not easy accessible PAHs by utilizing BN bond formations.
Publications
- “Enforced Planarity: A Strategy for Stable Boron-Containing π-Conjugated Materials”. Angew. Chem. Int. Ed. 2012, 51, 9977 – 9979
Araneda, Juan F.; Neue, Benedikt; Piers, Warren E.
- “Photochemical Synthesis of a Ladder Diborole: A New Boron-Containing Conjugate Material”. Angew. Chem. Int. Ed. 2012, 51, 8546 – 8550
Araneda, Juan F.; Neue, Benedikt; Piers, Warren E.; Parvez, Masood
