Photophysical and Computational Investigations of Bis(phosphine) Organoplatinum(II) Metallacycles

A series of endohedral and exohedral amine-functionalized ligands were synthesized and used in the construction of supramolecular D-2h rhomboids and a D-6h hexagon. These supramolecular polygons were obtained via self-assembly of 120 degrees dipyridyl donors with 180 degrees or 120 degrees diplatinum precursors when combined in 1:1 ratios. Steady-state absorption and emission spectra were collected for each ligand and metallacycle. Density functional theory (DFT) and time-dependent DFT calculations were employed to probe the nature of the observed optical transitions for the rhomboids. The emissive properties of these bis(phosphine) organoplatinum metallacycles arise from ligand-centered transitions involving pi-type molecular orbitals with modest contributions from metal-based atomic orbitals. The D-2h rhomboid self-assembled from 2,6-bis(4-pyridylethynyl)aniline and a 60 degrees organoplatinum(II) acceptor has a low-energy excited state in the visible region and emits above 500 nm, properties which greatly differ from those of the parent 2,6-bis(4-pyridylethynyl)aniline ligand.