Electronic structure and optical properties of electroluminescent spiro-type molecules

The electronic structure and optical properties of the propeller-shaped spiro molecules, $\mathrm{2,2\prime -bis(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl)-9,9\prime -spirobifluorene},$ and 2,2′,7,7′-tetrakis (biphenyl-4-yl)-9,9-spirobifluorene, have been studied by photoelectron spectroscopy, Raman spectroscopy, and spectroscopic ellipsometry. The experimental spectra are analyzed with the help of results from quantum-chemical calculations. The excellent agreement between experiment and theory allows for a detailed characterization of the frontier electronic structure and lowest-energy optical transitions in these novel compounds. It follows that most of the electronic and optical properties of the these spiro-molecules can be deduced by consideration of a single branch; in this case a sexi-phenyl and PBD branch. In particular, although the branches in the spiro molecules are perpendicular to each other, there is considerable interaction at the spiro-center between the π-electron systems of the two branches, indicating, among other things, that chemistry involving either branch is dependent on the other branch.