Generation of N->B-Ladder-type Structures via Cycloaddition Reactions

• Applicant: Professor Dr. Peter Bäuerle, since 10/2020
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Preparatory and Physical Chemistry of Polymers
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 320261689

A general topic of our work is the development of methodologies that give access to pi conjugated oligomers und polymers that contain Lewis acidic tricoordinate boron centers and basic N-heterocycles in a suitable regiostructure that allows for intramolecular N->B- coordination. The molecular geometry and electronic properties of the resulting conjugated systems are strongly affected by this interaction. Generally, a planarization of the pi-system and concurrent extended conjugation is observed. This leads to more effective pi-stacking in the solid state, which in turn is deemed beneficial for charge transport in organic semiconductors. The project outlined herein follows a new strategy that is aimed at building up the required N-heterocycles from alkynyl- and cyano-functionalized boranes via 1,3-dipolar [3+2]- and Hetero-Diels-Alder-[4+2]-cycloaddition reactions.Preliminary experiments outlined herein, demonstrate that both copper catalyzed azide-alkyne cycloaddition (CuAAC, leading to 1H-1,2,3-triazols) and alkyne-diazoalkane cycloaddition (ADAC, leading to 1H-pyrazoles) can be employed to this end. Detailed analyses of a series of triazole-containing boranes via electrochemical and UV-vis spectroscopic methods, as well as anion binding studies, demonstrate that the optical and electronic properties of said compounds can be incrementally varied over a wide range.The goal of the project is the expansion of the scope of employable boranes and cycloaddition reactions in order to make a range of electronically and structurally varied pi-conjugated N->B-systems available. The main focus of our work will be the synthesis and electronic characterization of the target structures. However, suitable compounds will be also characterized through incorporation into organic electronic devices, in cooperation with specialized research groups: The investigated boranes show high electron affinities and undergo reversible electrochemical reduction. Consequently, the compounds shall eventually be employed as semiconductors in n-channel organic field effect transistors (OFETs) and may also be incorporated into organic light emitting diodes (OLED) and light emitting electrochemical cells (LECs), either as electron transport material, or as actively emitting component.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Privatdozent Dr. Frank Pammer, until 9/2020