Syntheses, photophysical, electroluminescence and computational studies of rhenium(i) diimine triarylamine-containing alkynyl complexes

Abstract

A series of triarylamine-containing rhenium(I) diimine alkynyl complexes has been synthesized and some of their X-ray crystal structures have been determined. Low-energy transition bands at 402–444 nm were observed in the electronic absorption spectra and were tentatively assigned as an admixture of [dπ(Re) → π*(diimine)] metal-to-ligand charge-transfer (MLCT) and [π(CC−C₆H₄–R) → π* (diimine)] ligand-to-ligand charge-transfer (LLCT) transitions. They were found to give emission upon photo-excitation in the solid state and in fluid solution at room temperature and their emissive origins were assigned as derived predominantly from the triplet ³MLCT excited state, mixed with ³LLCT character as well as the ³IL state. Electrochemical studies revealed that the first oxidation process was mainly alkynyl ligand-based with mixing of the metal-centred contribution, whereas the first reduction was attributed to the ligand-centred reduction of the diimine ligand. Computational studies have been performed to provide further insight into the electrochemical and photophysical properties. The photochemical properties with triphenylamine were also studied by quenching experiments and time-resolved transient absorption spectroscopy. Some of these complexes were able to act as emitters in OLED devices and their electroluminescence (EL) behaviour was investigated.