Large enhancement of intersystem crossing in polyfluorenes by iridium-complex doping

Abstract

Photoinduced absorption is used to study the intersystem crossing (ISC) rate of two polyfluorenes doped with iridium (III) tris[2-(4-totyl)pyridinato-N,C2]. It is found that the triplet exciton lifetime of polyfluorene is reduced by the dopants. But instead of decreasing, the population density of polyfluorene triplet exciton increases by almost one order of magnitude. The finding shows that the ISC rate can increase over 100 times due to the spin-orbital interaction with the Ir ion even though it is covered by the ligands. Specifically, the ISC lifetime changes from the intrinsic value of 62 ns to as short as 0.28 ns upon 10% doping.