Photo- and thermo-oxidative stability of aromatic spiro-linked bichromophoric cross-shaped molecules

An extensive investigation of the photostability and the thermo-oxidative s tability is presented for 2,2',7,7'-tetrakis(biphenyl-4-yl)-9,9'-spirobiflu orene and 2,2',4,4',7,7'-hexakis(biphenyl-4-yl)-9,9'-spirobifluorene. Both compounds are conjugated fully aromatic systems that are being discussed as active functional materials for a variety of advanced applications. The ef fect of atmosphere, sample thickness and preparation procedure on photo-oxi dative degradation are investigated in detail by absorption and fluorescenc e spectroscopy. Distinct mechanisms are described in terms of relevant para meters such as the quantum yields of the photo-oxidation and the fluorescen ce. No oxidative degradation could be detected under nitrogen. In ambient a ir a strong decrease of the fluorescence performance is found due to effect ive quenching by defective chromophores. Chemiluminescence investigations w ere performed to characterise the thermo-oxidative behaviour in the tempera ture region between 300 and 450 K. It becomes clear that even a stable chem ical structure such as the investigated aromatic system does not guarantee sufficient photostability with regard to light emitting properties.