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 (IC6 F5 and I2 C6 F4 ). Compounds 1 a and 2 a (L/Y=DMSO/Cl) afford the adducts 1 a⋅⋅⋅I2 C6 F4 and 2 a⋅⋅⋅I2 C6 F4 , which feature I⋅⋅⋅Sbtpy /I⋅⋅⋅πbtpy and I⋅⋅⋅ODMSO /I⋅⋅⋅Cl short contacts, respectively. The phosphane-cyanide derivatives 1 c and 2 c (L/Y=PPh3 /CN) co-crystallise with both IC6 F5 and I2 C6 F4 . None of the phpy-based species 3 a-3 c participated in XB interactions. Although the native complexes are rather poor luminophores in the solid state (Φem =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.