Intriguing Effects of Halogen Substitution on the Photophysical Properties of 2,9-(Bis)halo-Substituted Phenanthrolinecopper(I) Complexes

International audienceThree new copper(I) complexes [Cu(LX)2] + (PF6-) (where LX stands for 2,9-di-halo-1,10-phenanthroline and X = Cl, Br and I) have been synthesized in order to study the impact of halogen substituents tethered in α position of the chelating nitrogen atoms on their physical properties. Photophysical properties of these new complexes (hereafter named Cu-X) were characterized both in their ground and excited states. Femtosecond ultrafast spectroscopy revealed that early photo-induced processes are faster for Cu-I than for Cu-Cl or Cu-Br, both showing similar behaviors. Their electronic absorption and electrochemical properties are comparable to benchmark [Cu(dmp)2] + (where dmp stands for 2,9-dimethyl-1,10-phenanthroline); furthermore, their optical features were fully reproduced by TD-DFT and Ab Initio Molecular Dynamics (AIMD) calculations. All three complexes are luminescent at room temperature, showing that halogen atoms bound to positions 2 and 9 of phenanthroline are sufficiently bulky to prevent strong interactions between the excited Cu complexes and solvent molecules in the coordination sphere. Their behavior in the excited state, more specifically the extent of photoluminescence efficiency and its dependence on temperature, is however strongly dependent on the nature of the halogen. A combination of ultrafast transient absorption spectroscopy, temperature dependent steady state fluorescence spectroscopy and 2 computational chemistry allows to gain a deeper understanding of the behavior of all three complexes in their excited state