Phosphorescence Quenching by Conjugated Polymers

Energy transfer between phosphors and conjugated polymers was investigated using a fluorene trimer (F3) as a model conjugated material. The phosphors studied were bis-cyclometalated iridium complexes (FP, PPY, BT, PQ, and BTP), with triplet energies of 2.6, 2.4, 2.2, 2.1, and 2.0 eV, respectively (based on phosphorescence spectra). Stern-Volmer analysis of luminescent quenching shows that energy transfer from either FP or PPY to F3 is an exothermic process with Stern-Volmer quenching constants (kqSV) of near 109 M-1 s-1 while energy transfer from BT, PQ, and BTP is endothermic (kqSV = 107-106 M-1 s-1). On the the basis of above results, the triplet energy of F3 is estimated to be less than 2.3 eV (530 nm). This study suggests that conjugated polymers, which typically have lower T1 energies than F3, should also quench phosphorescent emission in thin films and organic light-emitting diodes (OLEDs) incorporating these and related phosphorescent dopants.