The radiationless transition rates from metal-to-ligand charge-transfer excited states of [Ru(phen)(3)](2+) (phen = 1,10-phnanthroline) and its analogues were investigated in terms of the Huang-Rhys factors (S) using luminescence measurements and quantum chemical calculations. From the luminescence spectral fitting, it was found that not only S-M for medium frequency mode but also S-L for low frequency mode was significant for the nonradiative process. Huang-Rhys factors predicted by the conventional quantum chemical method were in agreement with the experimental values, S-M and S-L. (c) 2005 Elsevier B.V. All rights reserved.