Triplet level-dependent photoluminescence and photoconduction properties of pi-conjugated polymer thin films doped by iridium complexes

Abstract

Triplet energy level-dependent decay pathways of excitons populated on iridium (Ir) complexes within pi-conjugated polymeric matrices were studied by means of photoluminescence (PL) and photoconduction action spectroscopy. We chose a set of matrices, poly(9-vinylcarbazole) (PVK), poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6), poly [2-(5'-cyano-5'-methyl-hexyloxy)-1,4-phenylene] (CNPPP), and poly [2-(5'-cyano-5'-methyl-hexyloxy)-1,4-phenylene-co-pridine] (CNPPP-py10 and CNPPP-Py20), having triplet energy levels ranging from 2.2 up to 3.0 eV. As Ir-complex dopants, we selected three phosphorescent emitters, iridium(III)bis(2-(2'-benzothienyl) pyridinato-N-acetylacetonate) (Ir(btP)(2)acac), iridium(III)fac-tris(2-phenyl pyridine) (Ir(PPY)A and iridium(III)bis[(4,6-fluorophenyl)-pyriclinato-N,C-2']picolinate (Flrpic), having triplet energy levels of 2.1, 2.5, and 2.7eV, respectively. It was found that the triplet emission from the dopants, being populated via energy transfer from the matrices, was strongly dependent on the matching of triplet energy levels between matrix polymers and Ir-complexes. Photocurrent action spectra confirm effective exciton confinement at the dopants sites in the case of PVK matrix systems. (C) 2008 Elsevier B.V. All rights reserved.