Fine tuning the electronic properties of [M(bpy)(3)](2+) complexes by chemical pressure (M=Fe2+, Ru2+, Co2+, bpy=2,2 '-bipyridine)

The optical and photophysical properties of three classic transition metal complexes, namely [Fe(bpy)(3)](2+), [Ru(bpy)(3)](2+) and [Co(bPY)(3)](2+), can be fine-tuned by doping them into a variety of inert host lattices. The effects of the guest-host interactions are discussed in terms of a chemical pressure. In this chapter we show how this chemical pressure can accelerate the high-spin-->low-spin relaxation in the iron complex by more than three orders of magnitude, how it can increase the activation energy of the thermal quenching of the famous orange luminescence of the ruthenium complex by a factor of two, and how it can push the high-spin cobalt complex to become a spin-crossover complex.