Photoluminescence of platinum(II) diethynylphenanthroline organometallic complexes with bis-arylethynyl derivatives in solution and solid state

Abstract

Platinum(II) phenanthroline organometallics, Pt(3,8-Phen≡H)(≡Ph-R)2 (1H–11H), of 11 respective arylethynyl ligands with different substituents: R = H (1H), 4-F (2H), 3-F (3H), 2-F (4H), 4-Me (5H), 4-CF3 (6H), NO2 (7H), 4-COOMe (8H), 4-t-Bu (9H), 3,5-di-CF3 (10H), and 3,5-di-t-Bu (11H) were prepared from our reported complexes, Pt(3,8-Phen≡TMS)(≡Ph-R)2, by a deprotection reaction of a trimethylsilyl group. The luminescence and the DFT calculations of the 11 present organometallics clearly supported the assignment of phosphorescence from the mixed transition of 3MLCT/3LLCT (LLCT = ligand-to-ligand charge transfer) in solution state. In solid state, the emission maximum peak values in the spectra of many complexes in 22 platinum organometallics occurred in the long wavelength area over 700 nm, and their emissions were assigned the phosphorescence from the transition of a metal-metal-to-ligand charge transfer, the so-called 3MMLCT. This is related to the diversity of intermolecular interactions as Pt-Pt and π-π interactions in solid state. On the other hand, the emission peak values in the spectra of some complexes occurred in the short-wavelength area less than 600 nm. The complex Pt(3,8-Phen≡TMS)(≡Ph-3,5-di-CF3)2 showed a particularly strong and vibronic emission, and this phenomenon is presumed to be attributable to the aggregation-induced emission.