An Experimental and Theoretical Approach to the Photophysical Properties of Some Rh and Ir Complexes Incorporating the Dipyrromethene Ligand

Rh and Ir complexes that contain meso-(p-methoxyphenyl)dipyrromethene (dipy) and phenylpyridine (ppy) ligands {i.e., [Rh(dipy)3], [Rh(ppy)2(dipy)] and [Ir(ppy)2(dipy)]} have been prepared and their electrochemical and luminescence behaviour are discussed and compared to results of theoretical calculations. The oxidation and reduction potentials, in agreement with the time-dependent (TD)-DFT calculations, indicate clearly that the HOMOLUMO transitions are governed by the dipy ligand, which controls also the triplet excited-state emission. However, in luminescence, the two Rh complexes exhibit, in addition to a dipy-centred triplet emission, luminescence from the singlet excited state, which predominates at room temperature, due to a less important influence of the heavy-metal effect in Rh than in Ir complexes. Although the TD-DFT results are in very good agreement with the experimental emission spectra from the dipy-centred triplet excited state, this is not the case for the absorption spectra of the complexes and free dipy ligand.