Photoluminescence of a New Material: Cyclometalated C∧C* Thiazole-2-ylidene Platinum(II) Complexes

A new class of platinum(II) compounds, the 4,5-dimethyl-3-aryl-thiazole-2-ylidene platinum(II) acetylacetonato complexes, are described. Their efficient phosphorescent emission at room temperature makes them suitable for potential applications in organic light-emitting diodes. A new synthetic pathway that allows the preparation of a broad range of different N-arylthiazole-2-thiones and their subsequent conversion into the corresponding N-arylthiazolium perchlorate and hexafluorophosphate salts has been developed. Not only electron-rich (4-OMe, 4-Me, 3-Me) N-arylthiazoles but also electron-deficient ligands with a cyano or an ester group could be synthesized. From commercially available anilines N-arylthiazolium perchlorate and hexafluorophosphate salts were synthesized via ring closure of in situ generated N-aryldithiocarbamate salts followed by a sulfur-oxidation/-substitution protocol to the air-stable carbene precursors. All reactions were performed in multigram scale in good yields. The synthesis of the corresponding platinum(II) complexes involves generating the corresponding N-arylthiazole-silver(I)-carbene complexes, transmetalation to platinum, cyclometalation, and reaction with acetylacetonate (acac). Solid-state structures of two N-arylthiazole-2-thiones, one Narylthiazolium salt, and three N-arylthiazole-2-ylidene-platinum(II) complexes complement the analytic characterization including Pt-195 NMR. The unsubstituted complex 4,5-dimethyl-3-phenylthiazole-2-ylidene-platinum(II)-acac was additionally characterized by 2D-NMR techniques (COSY, HSQC, HMBC, NOESY). Photoluminescence measurements were performed in amorphous poly(methyl methacrylate) films and revealed bluish-green emission maxima (similar to 500 nm) independent of the electronic structure of the thiazoles, whereas the variation of the substitution pattern at the cyclometalating aryl system led to excellent quantum efficiencies and decay lifetimes of 8.1-21.4 mu s.