Geometry relaxation in the excited states and its effects on the electronic properties of the Er(8-hydroxyquinolate)3 complex

We present the results of a semiempirical study of the geometry relaxation effects on the electronic properties of the Er(8-hydroxyquinolinate)3 complex, chosen as a model system in which energy transfer takes place. Geometry distortion in the excited states can affect several photophysical properties such as Stokes shifts, emission in target regions of the spectrum, lifetimes and others. In spite of this fact, in the majority of the theoretical works geometry rearrangements induced by photon absorption are simply ignored, due also to practical difficulties connected to the size of the complexes.In this paper we will use a simple semiempirical approach for the theoretical calculation of the excitation energies of the organic part of the complex, and we will show that the explicit consideration of the geometrical relaxation allows to identify (at least in this case) the most energetically favourable channel for the population of the triplet state.