Tripodal Ru(II) complexes with conjugated and non-conjugated rigid-rod bridges for semiconductor nanoparticles sensitization

Three tripodal Ru(II)-polypyridyl complexes have been synthesized as models to study long-range electron transfer in TiO2 semiconductor nanoparticles thin films, in particular to study the effect of the conjugation of the bridge containing the Ru complex and for distance dependence studies. The tripodal sensitizers, which are 1,3,5,7-tetraphenyladamantane derivatives having three COOMe anchoring groups and one rigid-rod bridge substituted with a Ru(II) complex, are the longest prepared to date (Ru-to-footprint distance ∼24 Å). Two have a rigid-rod bridge made of two p-ethynylphenylene units (Ph-E)2 capped with a 4-2,2′-bipyridyl (bpy) ligand or a 5-1,10-phenanthrolinyl (phen) ligand for the Ru complex. The third tripod, which contains a bpy ligand for the Ru complex, has one bicyclo[2.2.2]octylene (Bco) unit in place of a p-phenylene (Ph) unit and is the first example of a tripodal sensitizer with a non-conjugated bridge.