PROPERTIES OF MIXED-LIGAND CYCLOMETALATED PLATINUM(II) COMPLEXES DERIVED FROM 2-PHENYLPYRIDINE AND 2-(2-THIENYL)PYRIDINE - VOLTAMMETRIC, ABSORPTION AND EMISSION STUDIES

The spectroscopic and electrochemical properties of some cyclometalate d Pt(II) complexes derived from 2-phenylpyridine, [Pt(ppy)AB], and 2-( 2'-thienyl)pyridine, [Pt(tpy)AB], have been compared. A and B represen t various monodentate and bidentate ligands. When exchanging ppy with tpy the metal-to-ligand charge transfer, MLCT, as viewed by the struct ured absorption and emission bands, is shifted by ca. 3000 cm(-1) to l ower energy. The redox potentials for the two series of complexes, how ever, are most similar and depend only on the additional ligands A and B. The radiative lifetimes of the lowest excited state of the tpy com plexes are significantly longer than for the ppy complexes. The variou s data indicate that the lowest excited state of the tpy complexes has a larger contribution from the pi-character of the cyclometalated lig and. Since tpy complexes, contrary to most ppy complexes, are luminesc ent even at room temperature, it is concluded that this class of compl exes are better candidates for promoting luminescent species. The redo x potentials of the complexes are linearly related to Lever's electroc hemical parameters, E(L), with a slope of ca. 0.55 for reduction and c a. 0.65 for oxidation. The linear relationship breaks down for oxidati on potentials when A and B represent sterically hindered phosphines, p resumably due to oxidation of the heteroatoms.