The title compounds were recently demonstrated to be useful as luminescent
electron transport materials in organic light emitting diodes. Here, we pre
sent studies of the fluorescence of the homologues with chain lengths betwe
en 2 and 10 carbon atoms. Dilute solutions of the investigated compounds sh
ow absorption in the range between 410 and 490 nm and fluorescence between
475 and 555 nm. However, the columnar phase of the pure compounds exhibits
fluorescence at considerably larger wavelength (550-650 nn) and gives large
r fluorescence lifetimes. This behaviour can be explained by the formation
of excimers in the mesophase. The phase transitions to the liquid crystal s
tate are associated with a distinct change of the fluorescence intensity.