Phosphorescent platinum(II) complexes bearing pentafluorosulfanyl substituted cyclometalating ligands

The first examples of phosphorescent platinum(II) complexes bearing pentafluorosulfanyl (-SF₅) substituted cyclometalating ligands (C^N) are reported. These complexes are of the form [Pt(C^N)(pivacac)], where pivacac is 2,2’,6,6’- tetramethylheptane-3,5-dionate. Modifying the phenyl ring of the C^N ligand to incorporate one strongly electron-withdrawing -SF₅ group has important effects on the photophysical and electrochemical properties of the complex that are dependent on the regiochemistry of the substituent. In a meta position with respect to the Pt-C_C^N bond, the substituent exerts a predominantly stabilising effect on the lowest triplet excited state that red-shifts the emission of the complex compared to the reference [Pt(ppy)(pivacac)], 1, where ppy is 2-phenylpyridinato. When the -SF₅ group is located para to the Pt-C_C^N bond, it does not affect the triplet state directly, and the electron-withdrawing group stabilises the metal-based orbitals, resulting in a blue-shift of the emission. In the solid-state all three complexes are mechanochromic, and can display excimeric emission originating from intermolecular π-π* interactions, but the relative emission intensities of the monomeric and dimeric excited states correlate with the steric congestion of the metal centre, and in particular the regiochemistry of the -SF₅ group. We correlate these findings with observations in the crystal structures.