SYNTHESIS, CHARACTERIZATION, ABSORPTION-SPECTRA, AND LUMINESCENCE PROPERTIES OF ORGANOMETALLIC PLATINUM(II) TERPYRIDINE COMPLEXES

A series of new organometallic platinum(II) complexes containing terde ntate polypyridine ligands has been prepared and characterized. Their absorption spectra in 4:1 (v/v) MeOH/EtOH fluid solution at room tempe rature and luminescence in the same matrix at 77 K have been investiga ted. The new species are [Pt(terpy)Ph]Cl (3, terpy = 2,2':6',2''-terpy ridine, Ph = phenyl), [Pt(Ph-terpy)Cl]Cl (4, Ph-terpy = 4'-phenyl-2,2' :6',2''-terpyridine), [Pt(Ph-terpy)Me]Cl (5), and [Pt(Ph-terpy)Ph]Cl ( 6). The results have been compared with those for [Pt(terpy)Cl]Cl (1) and [Pt(terpy)Me]Cl (2). NMR data evidence that all the complexes but 3 and 6 oligomerize in solution leading to stacked species. The absorp tion spectra are dominated by moderately intense metal-to-ligand charg e-transfer (MLCT) bands in the visible region and by intense ligand-ce ntered (LC) bands in the UV region. All the compounds are luminescent in a 4:1 (v/v) MeOH/EtOH rigid matrix at 77 K, exhibiting a structured emission within the range 460-600 nm. This feature is assigned to for mally (LC)-L-3 excited states which receive substantial contribution f rom closely lying (MLCT)-M-3 levels. Complexes 1, 2, 4, and 5 also exh ibit a relatively narrow and unstructured luminescence band within the range 680-800 nm, which dominates the luminescence spectrum on increa sing concentration and exciting at longer wavelengths. The band is ass igned to a d sigma(metal) --> pi*(polypyridine) ((MMLCT)-M-3) state, originating from metal-metal interactions occurring in head-to-tail di mers (or polymers). A third broad band is shown by 1 and 4 under all c oncentration conditions and by 2 and 5 only in concentrated solutions and is attributed to excimeric species originating from sz-Jr interact ions due to stacking between polypyridine ligands.