TUNING OF THE CT EXCITED-STATE AND VALIDITY OF THE ENERGY-GAP LAW IN MIXED-LIGAND COMPLEXES OF RU(II) CONTAINING 4,4'-DICARBOXY-2,2'-BIPYRIDINE

Using a series of electron-donating ligands (non-chromophoric or substituted bpy/phen type) the energy of the charge transfer (CT) transition has been varied systematically in mixed ligand complexes of Ru(II). [Ru(dcbpy)2(L)] In all cases the lowest energy transition is Ru --> dcbpy CT. The lowering of the CT state energy is caused mainly by increased charge density at the Ru center (t2g level). A comparison of the spectral shift with redox potentials shows that nearly 25% of the increased charge density at the Ru-center is transferred to the dcbpy ligand via mixing of the d-pi-pi* orbitals. The variation in the emission lifetimes and quantum yields in this graded series of complexes is quantitatively interpreted in terms of the energy gap law.