A Tris‐Cyclometalated Iridium(III) Complex of 2‐(5,5‐Dioxido‐dibenzothiophen‐3‐yl)pyridine: Synthesis, Structural, Redox and Photophysical Properties

The first cyclometalated dibenzothiophene S , S ‐dioxide derivative, namely [ fac ‐2‐(5,5‐dioxidodibenzothiophen‐3‐yl)pyridine]iridium(III) ( 3 ) has been synthesised in high yield and characterised by X‐ray crystallography, solution electrochemistry, absorption and emission spectroscopy. The Ir atom has a fac ‐octahedral coordination with three chelating ligands ( A, B and C ); each Ir–N bond is in trans position to an Ir–C bond. In cyclic voltammetry experiments in dichloromethane, complex 3 undergoes a reversible metal‐centred Ir III /Ir IV oxidation at E 1/2 ox = +1.04 V vs. Ag/Ag + reference electrode. Complex 3 exhibits bright green photoluminescence ( λ max = 525 nm in toluene) from mixed 3 MLCT/ 3 π→π* states with quantum yield ( Φ PL ) of 0.26 in toluene solution. The phosphorescence emission decay follows first order kinetics, with a lifetime of 4.9 μs. A comparison of complex 3 with analogues 1 and 2 , where the dibenzothiophene S , S ‐dioxide unit is replaced by 9,9‐dihexylfluorene and N ‐hexylcarbazole respectively, establish that the substituent para to the Ir metal atom, i.e. CR 2 in 1 , NR in 2 and SO 2 in 3 , has a major influence on the redox and emission properties in this series. Organic light‐emitting diodes (OLEDs) were fabricated by spin‐coating techniques using a polyspirobifluorene copolymer (PSBF) as a host and complex 3 as dopant.In a single‐layer blend configuration ITO/PEDOT:PSS/PSBF: 3 (8 wt.‐%)/Ba/Al OLEDs showed pale blue/white light emission (CIE coordinates: x = 0.29, y = 0.31) arising from a combination of fluorescence from the host copolymer ( λ max = 450 nm) and phosphorescence from 3 ( λ max = 530 nm). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)