Long-wavelength NIR luminescence of 2,2′-bipyridyl-Pt() dimers achieved by enhanced Pt-Pt interaction

In this work, six Pt( ii ) complexes based on 4,4′-bis(triethylsilylethynyl)-2,2′-bipyridine ligand were designed and synthesized. The crystal structures of complexes 1 , 2 , 5 and 6 showed that these complexes adopt dimer structures with ultra-short intermolecular Pt Pt distances [3.1674(4)-3.1973(7) Å]. In the solid state, all complexes exhibited long-wavelength NIR luminescence with maximum emission centered at 1045 nm for 1 , 1062 nm for 2 , 939 nm for 3 , 1051 nm for 4 , 1037 nm for 5 , and 1029 nm for 6 . This is the first report on the Pt( ii ) dimer with luminescence exceeding 1000 nm. More importantly, 1062 nm of complex 2 is the longest emission wavelength of the reported 2,2′-bipyridyl-platinum( ii ) complex. Furthermore, these complexes also exhibited reversible mechanoluminescence property. Systematic studies on the crystal structure, photophysical properties and PXRD patterns revealed that the long-wavelength NIR luminescence of dimers is due to the enhanced MMLCT transitions, and the mechanism of reversible mechanoluminescence property involves changes in the strength of the Pt-Pt interaction caused by reversible alteration of intermolecular Pt Pt distances during the mechanical grinding-vapor absorbing process. Benefiting from the very strong intermolecular Pt-Pt interaction, 2,2′-bipyridyl-Pt( ii ) dimers have achieved long-wavelength near-infrared luminescence exceeding 1000 nm for the first time.