Iridium(III) Complexes Bearing Pyrene-Functionalized 1,10-Phenanthroline Ligands as Highly Efficient Sensitizers for Triplet-Triplet Annihilation Upconversion

Abstract

"Chemistry-on-the-complex" synthetic methods have allowed the selective addition of 1-ethynylpyrene appendages to the 3-, 5-, 3,8- and 5,6-positions of Ir^III -coordinated 1,10-phenanthroline via Sonogashira cross-coupling. The resulting suite of complexes has given rise to the first rationalization of their absorption and emission properties as a function of the number and position of the pyrene moieties. Strong absorption in the visible region (e.g. 3,8-substituted Ir-3: λ_abs =481 nm, ϵ=52 400 m^-1 cm^-1 ) and long-lived triplet excited states (e.g. 5-substituted Ir-2: τ_T =367.7 μs) were observed for the complexes in deaerated CH₂ Cl₂ . On testing the series as triplet sensitizers for triplet-triplet annihilation upconversion, those Ir^III complexes bearing pyrenyl appendages at the 3- and 3,8-positions (Ir-1, Ir-3) were found to give optimal upconversion quantum yields (30.2 % and 31.6 % respectively).

Keywords: iridium(III); phenanthroline; pyrene; triplet-triplet annihilation; upconversion.