Colour tuning by the ring roundabout : [Ir(C^N)2(N^N)]+ emitters with sulfonyl-substituted cyclometallating ligands

A series of cationic bis-cyclometallated iridium(III) complexes [Ir(C^N)2(N^N)]+ is reported. Cyclometallating
C^N ligands are based on 2-phenylpyridine with electron-withdrawing sulfone substituents in the phenyl
ring: 2-(4-methylsulfonylphenyl)pyridine (H1) and 2-(3-methylsulfonylphenyl)pyridine (H2). 2-(1HPyrazol-
1-yl)pyridine (pzpy) and 2-(3,5-dimethyl-1H-pyrazol-1-yl)pyridine (dmpzpy) are used as electronrich
ancillary N^N ligands. The complexes have been fully characterized and the single crystal structure
of [Ir(2)2(dmpzpy)][PF6]$MeCN has been determined. Depending on the position of the methylsulfonyl
group, the complexes are green or blue emitters with vibrationally structured emission maxima at 491,
523 nm for [Ir(1)2(N^N)][PF6] or 463, 493 nm for [Ir(2)2(N^N)][PF6] in MeCN solution. The marked
vibrational structure and the absence of a rigidochromic shift, together with theoretical predictions
based on density functional theory calculations, confirm the 3LC nature of the emitting triplet state. All
four complexes have relatively high photoluminescence quantum yields in de-aerated solution (53 to
77%). On going from solution to powder samples, the emission is red-shifted and the quantum yields are
considerably lower (#11%). The complexes were tested in light-emitting electrochemical cells (LECs)
achieving maximum luminances of 141 cd m2 when operated at 100 A m2 using pulsed current driving
conditions