Long-range resonantly enhanced triplet formation in luminescent polymers doped with iridium complexes

Abstract

The current drive to produce cheap, flexible plastic displays¹ has led to rapid improvements in device efficiency. Inclusion of highly phosphorescent heavy-metal organic complexes as dopants ensures that both singlet and triplet excitations formed on charge recombination can be used efficiently to emit light². However, the inclusion of these dopants affects the photophysics of the host in a surprising way, generating a ten- to twenty- fold instantaneous increase in the number of host triplet states, independent of host triplet energy, quenching up to 95% of all singlet states. Once created however, these triplets are only weakly quenched by the same mechanism. We ascribe this to a resonant, remote intermolecular heavy-atom effect that greatly increases the inter-system crossing rate of the host polymer³ arising through the strong overlap of the delocalized π orbitals of the host and ligands. This mechanism competes effectively with Förster energy transfer, and operates over large distances.