2,5-Diaryl 6-hydroxyphenalenones for Single-Molecule Junctions

A modular access to 2,5-diaryl 6-hydroxyphenalenone derivatives is developed and demonstrated by a small series of 5 molecules. Within this series, the structures 1 and 2 expose terminal methylsulfanyl anchor groups, enabling their integration in a single molecule junction. The modular synthesis is based on Suzuki cross coupling of the aryl substituents as boronic acid precursors with 5,8-dibromo-2-(tert.butyl)-4,9-dimethoxy-2,3-dihydro-1H-phenalen-1-one, and the subsequent transformation of the product to the desired 2,5-diaryl 6-hydroxyphenalenone in a reduction/deprotection sequence. The new structures are fully characterized and their optical and electrochemical properties are analysed. For the derivatives 1 and 2 suitable for single molecule junctions, the corresponding oxophenalenoxyl radicals 1R and 2R were obtained by oxidation and analysed by EPR-spectroscopy. Preliminary mechanical break junction experiments with 1 display the structure’s ability to form transient single molecule junctions. The intention behind the molecular design is to profit from the various redox states of the structure (including the neutral radical) as molecular switch in an electro-chemically triggered single molecule transport experiment.