A clear understanding of the lowest-excited3MLCT states of [Ru(bpy)3]2+and related systems in crystalline hosts of well-defined symmetry is outlined, based on a range of incisive experiments such as Zeeman, Stark, line narrowing and spectral hole-burning measurements. The lowest-excited3MLCT states of ruthenium complexes are localised. The intramolecular excitation energy transfer can be relatively slow (≈ 10 ns). In the [Os(bpy)3]2+complex analogous excitations are well described as coherent intramolecular excitons. Cases are found in which the small effect associated with selective deuteration leads to exciton localisation. The influence of nanoheterogeneity in solutions and glasses gives rise to a substantial inequivalence of the ligands, invariably leading to localization.