From the data in Figure and SI-3-2, we can characterize the effects of TEOA on the excited states of the complex. First, we didn't observe the formation of any new species, nor a reduction of the lifetime of the excited state in presence of TEOA, meaning that there is no electron transfer or quenching mechanism involved in the process. This point is in good agreement with the rate constant of electron transfer calculated for the ligand in THF (Section 2.1). In MeCN, TEOA has no effect on the transient dynamics and species observed bellow 1.5 ns. This is clearly different for ProCN, and BuCN for which we observed a clear increase of lifetime of the excited state localized on the ligand and consequently a different proportion of different LMCT conformers stabilized at 1.5 ns. It is notably worth noting that in BuCN:TEOA and ProCN:TEOA, the bleach signal is quasi-constant in the sub-ns time scale and a more efficient formation of the LMCT state is observed. The stabilization of the LMCT state result therefore of a complex synergy between the polarity of the solvent governing the MICT /TICT character of the excited state, and the viscosity of the TEOA solution constraining the twisting motion around the pyrene and bipyridine C-C bond. We concluded that, at high concentration, the TEOA molecules are not simple spectators of the photodynamic of the Pyr2Bpy derivatives, as it is often assumed but they can also deactivate the excited states of the ligand (MLCT sate) or affect the degree of -conjugation and charge transfer to the metal, notably by acting on the twisting dynamics around the interring C-C bond, that is a particularly critic parameter affecting the nature and the yield of formation the catalytically active LMCT species. We anticipate that this effect can be extending to other family of organo-metallic catalysts and should be more carefully considered in the design of the photocatalytic process.