Design, synthesis and excited-state properties of mononuclear Ru(II) complexes of tridentate heterocyclic ligands

Artificial photosynthetic systems that contain light-harvesting coordination complexes may one day replace conventional non-renewable sources of energy with renewable solar energy sources. Light-Harvesting Complexes (LHC) are important components of natural photosynthetic systems and are also sought after in artificial systems as well. Polynuclear photoactive complexes are therefore very attractive, and those based on stereogenic [Ru(2,2'-bipyridine)(3)](2+) are photophysically appealing, but difficult to obtain in a stereochemically pure form. On the other hand, polynuclear complexes based on the achiral [Ru(2,2':6',2 ''-terpyridine)(2)](2+) motif are easy to synthesise, however, these complexes are devoid of attractive excited-state properties. Hence strategies to increase the r.t. excited-state lifetime of these complexes would be of practical importance in vectorial electron and/or electron transfer in various optoelectronic applications. This tutorial review will report on the sophisticated synthetic strategies currently in use to enhance the photophysical properties of mononuclear Ru(II) complexes of tridentate ligands at room temperature.