Triplet exciton energy transfer in polyfluorene doped with heavy metal complexes studied using photoluminescence and photoinduced absorption

Abstract

Modulated photoinduced absorption and photoluminescence are used to study triplet-to-triplet Dexter energy transfer in Ir-complexes/polyfluorene blend systems. There is no Dexter energy transfer for red iridium (III)bis[2-(9,9-dibutylfluorenyl)-1-isoquinoline(acetylacetonate)] (DFIr) and red iridium (III) bis([2-(2-benzo-thienyl)pyridinatoN,C3] acetyl-acetonate) (BtpIr) dopants. Although green iridium(III)tris[2-(4-tolyl)pyridinato-N,C2] $[\mathrm{Ir}{(\mathrm{mppy})}_{3}]$ has no triplet confinement in polyfluorene host, it has clear evidence for Dexter energy transfer. Aggregation and dopant lifetime are shown to significantly affect the energy transfer. The presence of Dexter transfer implies the possibility to harvest triplet excitons of polyfluorene in polymer light-emitting diodes even without carrier trapping and triplet exciton confinement.