Molecular packing effects on the optical spectra and triplet dynamics in oligofluorene films

We report on the triplet spectra and dynamics in two types of oligomeric films deposited by two different techniques: thermal evaporation and spin coating. The different molecular arrangement in both films is manifested in a red shift of the absorption, PL, and T-1-T-n absorption spectra of the sublimated film relative to the spin-coated one. Triplet recombination dynamics studied with steady-state photoinduced absorption (PA) spectroscopy follow a dispersive bimolecular recombination model away from the trap filling regime. We obtained values for the triplet bimolecular recombination ratio (beta) of 3.4 x 10(-14) and 1.1 x 10(-15) cm(3) s(-1) for evaporated and spin-coated film, respectively, the difference being attributed to diverse molecular arrangement in both films.