Steric effect on excimer formation in planar Pt(ii) complexesElectronic supplementary information (ESI) available: Decay profiles and TD-DFT results. CCDC 1523132 and 1523133. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6cp08651a

In order to understand the steric influence on excimer formation in square planar metal complexes, three different Pt( ii ) complexes were prepared by modifying the substituents in the main ligand: Pt( ii )(dfppy)(acac) ( Pt-1 , where dfppy is difluorophenylpyridine, acac is acetylacetonate); the bulky triphenyl silyl (Ph 3 Si-) group was substituted at the pyridine moiety ( Pt-2 ) and at the phenyl moiety ( Pt-3 ) of the main ligand of Pt-1 . The Pt-complexes showed sky-blue emission at ∼460 nm. In addition, Pt-1 and Pt-3 showed excimer emission at ∼600 nm in the concentrated solution and the solid sample. The emission lifetimes and intensities for monomeric Pt-1 and Pt-3 showed strong concentration dependence. Indeed, the lifetime of the monomer was reduced in highly concentrated solutions due to excimer formation. The intrinsic emission lifetimes were determined as 364 ns ( Pt-1 ) and 300 ns ( Pt-3 ) by Stern-Volmer analysis, considering the self-quenched lifetime of monomer emission. Pt-2 did not show any excimer emission in the concentrated solution or solid sample. The crystal structures of Pt-1 and Pt-3 were analysed by X-ray crystallographic measurements. The results revealed that the LUMO moiety closely overlapped with that of another Pt-complex. In this study, based on the influence of steric hindrance of the bulky Ph 3 Si group, we concluded that the LUMO-LUMO interaction between the pyridine moieties of the main ligand is the main factor responsible for excimer formation. The LUMO-LUMO interaction between the pyridine moieties of the main ligand is the main factor responsible for excimer formation.