Synthesis, Characterization, Absorption Spectra, and Luminescence Properties of Organometallic Platinum(II) Terpyridine Complexes Giuseppe Arena, ²,‡ Giuseppe Calogero, ² Sebastiano Campagna,* ,² Luigi Monsu ` Scolaro,* ,²,‡ Vittorio Ricevuto, ² and Raffaello Romeo ²,‡ Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Universita ` di Messina, Messina, Italy, and Istituto di Chimica e Tecnologia dei Prodotti Naturali, (ICTPN-CNR), Sezione di Messina, Messina, Italy ReceiVed April 28, 1997 A series of new organometallic platinum(II) complexes containing terdentate polypyridine ligands has been prepared and characterized. Their absorption spectra in 4:1 (v/v) MeOH/EtOH fluid solution at room temperature and luminescence in the same matrix at 77 K have been investigated. The new species are [Pt(terpy)Ph]Cl (3, terpy ) 2,2′:6′,2′′-terpyridine, 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 absorption spectra are dominated by moderately intense metal-to-ligand charge- transfer (MLCT) bands in the visible region and by intense ligand-centered (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 formally 3 LC excited states which receive substantial contribution from closely lying 3 MLCT levels. Complexes 1, 2, 4, and 5 also exhibit a relatively narrow and unstructured luminescence band within the range 680-800 nm, which dominates the luminescence spectrum on increasing concentration and exciting at longer wavelengths. The band is assigned to a dσ*(metal) f π*(polypyridine) ( 3 MMLCT) state, originating from metal-metal interactions occurring in head-to-tail dimers (or polymers). A third broad band is shown by 1 and 4 under all concentration conditions and by 2 and 5 only in concentrated solutions and is attributed to excimeric species originating from π-π interactions due to stacking between polypyridine ligands. 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