Oligofluorene derivative in a host-guest system with a red-emitter: Molecular packing effect on the host bimolecular recombination and guest ASE threshold reduction

The dynamics of triplet recombination in fluorene trimers have been studied using steady state photoinduced absorption (PA) spectroscopy. We investigated two type of oligomeric films, deposited by different techniques: thermal evaporation and spincoating. The different molecular arrangement in both films is manifested in a red-shift of the absorption, PL and T1-Tn triplet PA spectra of the sublimated film relative to the spincoated one. Triplet recombination dynamics follow a dispersive bimolecular recombination model away from the trap filling regime. Moreover we report on the characteristics of a host-guest lasing system obtained by co-evaporation of the most promising oligofluorene derivative (T3) with the red-emitter 4-(dicyanomethylene)-2-methyl-6-(p- dimethylaminostyryl)-4H-pyran dye (DCM). The blend satisfies the necessary condition for an efficient FÖrster energy transfer to take place from T3 matrix to DCM molecules.