Rhenium(i) complexes with phenanthrolines bearing electron-withdrawing Cl and electron-donating CH₃ substituents - synthesis, photophysical, thermal, and electrochemical properties with electroluminescence ability

Five rhenium(i) tricarbonyl complexes incorporating 1,10-phenanthroline derivatives with electron-withdrawing Cl and electron-donating CH₃ substituents were synthesized, and their photophysical, thermal, and electrochemical properties, with electroluminescence ability were examined. The melting temperature of these complexes was found to decrease from 391 to 281 °C upon adding methyl groups and decreasing the number of chlorine atoms. Compounds bearing methyl substituents could form amorphous molecular materials with glass transition temperatures in the range 118-127 °C. Cyclic voltammetry measurements demonstrated that the complexes are electrochemically active with low energy band gaps in the range 2.24-2.46 eV. All complexes are photoluminescent, form films in the solid state, and blend with poly(9-vinylcarbazole) (PVK) and PVK:(2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole) (PBD), emitting light with λ_em from 560 to 599 nm. They exhibited large Stokes shifts of up to 323 nm in solutions and up to 220 nm as film on a glass substrate. They were tested as guests in organic light-emitting diodes. As hosts, PVK and a binary matrix consisting of PVK with PBD were applied. The ability of the investigated complexes to emit light under an applied voltage was shown.