Improvement of the Photophysical Performance of Platinum-Cyclometalated Complexes in Halogen-Bonded Adducts

Three groups of luminescent platinum complexes [Pt(C^N)(L)(Y)] [C^N=benzothienyl-pyridine (1), bezofuryl-pyridine (2), phenyl-pyridine (3); L/Y=DMSO/Cl (a), PPh₃/Cl (b), PPh₃/CN (c)] have been probed as halogen-bond (XB) acceptors towards iodofluorobenzenes (IC₆F₅ and I₂C₆F₄). Compounds 1a and 2a (L/Y=DMSO/Cl) afford the adducts 1aI₂C₆F₄ and 2aI₂C₆F₄, which feature IS_btpy/Iπ_btpy and IO_DMSO/ICl short contacts, respectively. The phosphane-cyanide derivatives 1c and 2c (L/Y=PPh₃/CN) co-crystallise with both IC₆F₅ and I₂C₆F₄. None of the phpy-based species 3a-3c participated in XB interactions. Although the native complexes are rather poor luminophores in the solid state (Φ_em=0.023-0.089), the adducts exhibit an up to 10-fold increase of the intensity with a minor alteration of the emission energy. The observed gain in the quantum efficiency is mainly attributed to the joint influence of non-covalent interactions (halogen/hydrogen bonding, π-π stacking), which govern the crystal-packing mode and diminish the radiationless pathways for the T₁→S₀ transition by providing a rigid environment around the chromophore.