Photophysics and reverse saturable absorption of cationic dinuclear iridium(iii) complexes bearing fluorenyl-tethered 2-(quinolin-2-yl)quinoxaline ligands

Abstract

The synthesis, photophysics and reverse saturable absorption of two cationic dinuclear Ir(III) complexes bearing fluorenyl-tethered 2-(quinolin-2-yl)quinoxaline (quqo) ligands are reported in this paper. The two complexes possess intense and featureless diimine ligand localized ¹ILCT (intraligand charge transfer)/¹π,π* absorption bands at ca. 330 and 430 nm, and a weak ^1,3MLCT (metal-to-ligand charge transfer)/^1,3LLCT (ligand-to-ligand charge transfer) absorption band at >500 nm. Both complexes exhibit weak dual phosphorescence at ca. 590 nm and 710 nm, which are attributed to the ³ILCT/³π,π* and ³MLCT/³LLCT states, respectively. The low-energy ³MLCT/³LLCT state also gives rise to a moderately strong triplet excited-state absorption at 490–800 nm. Because of the stronger triplet excited-state absorption than the ground-state absorption of these complexes at 532 nm, both complexes manifest a moderate reverse saturable absorption (RSA) at 532 nm for ns laser pulses. Expansion of the π-conjugation of the fluorenyl-tethered diimine ligand in Ir-1 causes a slight red-shift of the ¹ILCT/¹π,π* absorption bands in its UV-vis absorption spectrum and the ³MLCT/³LLCT absorption band in the transient absorption spectrum and slightly enhances the RSA at 532 nm compared to that in Ir-2. This work represents the first report on dinuclear Ir(III) complexes that exhibit RSA at 532 nm.