Phosphorescent platinum(II) complexes bearing pentafluorosulfanyl substituted cyclometalating ligands
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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-CC^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-CC^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.
Henwood , A F , Webster , J , Cordes , D B , Slawin , A M Z , Jacquemin , D & Zysman-Colman , E 2017 , ' Phosphorescent platinum(II) complexes bearing pentafluorosulfanyl substituted cyclometalating ligands ' RSC Advances , vol 7 , pp. 25566-25574 . DOI: 10.1039/C7RA03190D
Copyright 2017 the Authors. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
EZ-C acknowledges the University of St Andrews for financial support. We thank Johnson Matthey and Umicore AG for the gift of materials. We would like to thank the Engineering and Physical Sciences Research Council for financial support for Adam Henwood: EPSRC DTG Grants: EP/J500549/1; EP/K503162/1; EP/L505097/1. We thank the EPSRC UK National Mass Spectrometry Facility at Swansea University for analytical services. DJ thanks the LumoMat RFI project for support. This research used computational resources of (i) the GENCI-CINES/IDRIS; (ii) CCIPL (Centre de Calcul Intensif des Pays de Loire); (iii) a local Troy cluster.
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