The well-known terpyridine (tpy) ligand serves as an archetypical chelate in a series of photo- and/or redox-active metal complexes. Owing to their facile preparation and synthetic modifaction, ruthenium complexes have attracted particular interest, aiming at improved photophysical properties. In the last decade, new tris-chelates have emerged to enhance the weak ligand field of tpy by a stronger donor set and/or improved geometrical features. On this rational, a series of diquinolinylpyridine-based (dqp) complexes were explored, which display an exceptional combination of geometrical features of tpy and long excited state lifetimes in the microsecond regime, including an enhanced complex' photostability. The very large bite angle ('>180�') leads to an out-of-plane twisting of dqp upon coordination, which results in substantial intramoelcular p-p-stacking (of quinolines) and a helical chiralty of the meridonal complexe, and further to the occurrence of facial isomers. On the basis of the established modular ligand syntheses for the N-N-N ligands, the systematic replacement of one nitrogen-heterocycle by a cyclometalling or carbenoidal donor is explored. Such substitution conventionally leads to red-shifted (pan-chromatic) absorption and the localization of the excited state (manifold). The synthetic protocol is detailed and the optical and electrochemcial properties of the corresponding ruthenium complexes are presented, which are believed to become of relevance in solar energy conversion.

Beyond terpyridines: Non-planar tridentate ligands featuring carbenoidal and cyclometallating donors

248th National Meeting (2014)

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