Organic Synthesis towards Rubicene and Substituted Derivatives for the Spectroscopic Assesmnet of New and Effective Singlet Fission Chromophores

Sammanfattning

Solar energy harvesting has seen an immense increase in popularity over the last decade, and in the incessant search of ways to further increase the efficiency of solar cells, an ultrafast photophysical process called Singlet Fission (SF) has been highlighted as a promising approach to mitigate thermalization. A prospect with great potential for being a photostable chromophore that might undergo effective SF is Rubicene (Rc), however little to no research has been done on it with respect to SF. In this report, a study consisting of two main parts is presented: the attempt at synthesising Rc and two derivatives (5,12-di-cyano rubicene and 5,12-di-tert-butyl-rubicene) through a proposed two-step procedure involving a Suzuki cross coupling reaction followed by a Scholl reaction; and the assessment of the potential of SF to occur within the obtained products with the help of steady state and time resolved spectroscopic techniques. The synthesis of Rc was successful, yielding a ruby red powder (210 mg, 60%) which was used for the preparation of thin films for spectroscopic analysis. However, both derivatizations using the Suzuki reaction failed unexpectedly, as low yields and impurities were observed for the cyano-substituted intermediate, and low conversion towards the di-substituted t-Bu intermediate was seen. The reason for this is not fully understood, but changes in the reaction systems such the use of different solvents and other ligands on the Pd(0) catalyst are advised for future work. Spectroscopic results were obtained for Rc that point towards the strong likelihood of an ultrafast process, presumably SF, taking place in films as suggested by fluorescence lifetime, τFl of 66.4 ps. A fluorescence quantum yield, ΦFl of 32% in solution and the stable S1-spectrum of Rc in a time span of up to 8 ns (from fsTA-experiments) suggest negligible intersystem crossing on these time scales.