Photo- and thermo-oxidative stability of aromatic spiro-linked bichromophoric cross-shaped molecules
2000
An
extensive investigation of the photostability and the thermo-oxidative stability is presented for 2,2′,7,7′-tetrakis(biphenyl-4-yl)-9,9′-spirobifluorene 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 effect of atmosphere, sample thickness and preparation procedure on
photo-oxidative degradation are investigated in detail by absorption and fluorescence spectroscopy. Distinct
mechanisms are described in terms of relevant parameters such as the quantum yields of the photo-oxidation
and the fluorescence. No oxidative degradation could be detected under nitrogen. In ambient air a
strong decrease of the fluorescence performance is found due to effective quenching by defective chromophores.
Chemiluminescence investigations were performed to characterise the thermo-oxidative behaviour in the
temperature region between 300 and 450 K. It becomes clear that even a stable chemical structure such
as the investigated aromatic
system does
not guarantee sufficient
photostability with regard to light emitting properties.
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