A study of the photophysical mechanisms controlling the luminescence lifetimes of a series of Ru^II complexes based on the same [Ru³⁺–hat^˙–]* luminophore (hat = 1,4,5,8,9,12-hexaazatriphenylene), and extending from monometallic building blocks to polynuclear compounds, is presented, together with the relevant spectroscopic and redox data. The parameters which characterise these different mechanisms, i.e. the radiative and nonradiative deactivation rate constants of the ³MLCT (metal to ligand charge transfer) state and the thermal activation from this state to the ³MC (metal centred) and/or to another ³MLCT state, have been determined from the analyses of the curves obtained by plotting the lifetimes or intensities of luminescence as a function of temperature. The mathematical and experimental limitations of the analysis method have been investigated and determination of the parameters has been improved by using a new global analysis algorithm. Interestingly the comparison of the data for the monometallic and polynuclear complexes indicates that the (Ru³⁺–hat^˙–)* luminophore, which is common for the whole series, presents characteristics that change when the hat becomes a bridging ligand, i.e. those that depend on the vibration modes of the complex. Moreover, for these polynuclear compounds, there is no contribution of the ³MC state to the mechanism of control of the luminescence lifetime.