Tailoring Colors by O Annulation of Polycyclic Aromatic Hydrocarbons

The synthesis of O-doped polyaromatic hydrocarbons, in which two polycyclic aromatic hydrocarbon subunits are bridged through one or two O atoms, has been achieved. This includes high-yielding ring-closure key steps that, depending on the reaction conditions, yield the formation of either furanyl or pyranopyranyl linkages through intramolecular C-O bond formation. Comprehensive photophysical measurements in solution showed that these molecules feature exceptionally high emission yields and tunable absorption properties throughout the UV-vis spectral region. Electrochemical investigations showed that in all cases the O-annulation increases the electron donor capabilities by raising the HOMO energy level with the LUMO energy level being less affected. Moreover, third-order NLO measurements of solutions or thin films containing the dyes displayed very good second hyperpolarizibility values. Importantly, PMMA films containing the pyranopyranyl derivatives displayed weak linear absorption and NLO absorption compared to the nonlinearity and NLO refraction, respectively, revealing to be exceptional organic materials for photonic devices.