Iridium(III) Complexes with Sulfonyl and Fluorine Substituents: Synthesis, Stereochemistry and Effect of Functionalisation on their Photophysical Properties

The synthesis and photophysical and electrochemical characterisation of new heteroleptic iridium complexes with electron-withdrawing sulfonyl groups and fluorine atoms bound to phenylpyridine ligands are reported. The emission energy of these materials strongly depends on the position of the sulfonyl groups and on the number of fluorine substituents. A 90 nm wide tuning range of photoluminescence from the blue-green (lambda(em)=468nm) of iridium(III)bis[2-(4'-benzylsulfonyl)-phenylpyridinato-N,C2'][3-(pentafluoro-phenyl)-pyridin-2-yl-1,2,4-triazolate] to the orange (lambda(em)=558nm) of iridium(III)bis[2-(3'-benzylsulfonyl)phenyl-pyridinato-N,C2'](2,4-decanedionate) has been achieved. Emission quantum yields ranging from 47 to 71% have also been found for degassed solutions of the complexes, and a surprisingly high value of 16% was recorded for iridium (III) bis[2-(5'-benzylsulfonyl-3',6'-difluoro)phenylpyridinato-N,C2'](2,4-decanedionate) in air-equilibrated dichloromethane. A unusual stereochemistry of the benzylsulfonyl-substituted dimer and heteroleptic complexes has been detected by H-1 NMR spectroscopy, and is characterised by the mutual cis disposition of the pyridyl nitrogen atoms of the phenylpyridine ligands, which differs from the most common trans arrangement reported in the literature.