Photoluminescence of ruthenium complexes with molecules exhibiting twisted internal charge transfer states

Abstract

The occurrence of dual fluorescence in ruthenium complexes containing dimethylaminobenzonitrile (DMABN) has been studied at liquid nitrogen and room temperatures. It was concluded that in the [Ru II(NH 3) 5DMABN] 2+, [Ru III(NH 3) 5DMABN] 3+ and [Ru II(bipy) 2Cl(DMABN)] + complexes (bipy ≡ bipyridyl) a typical twisted internal charge transfer (TCT) fluorescence of DMABN appears upon excitation on a π-π * ligand absorption band. The ratio of the two luminescence band intensities is modified with respect to the free ligand. The excitation of [Ru(NH 3) 5DMABN] n+ on a metal-to-ligand charge transfer (MLCT) band gives rise to fluorescence with maxima at 378 nm (77 K) and 393 nm (room temperature) for [Ru(NH 3) 5DMABN] 2+ and at 435 nm (room temperature) and 450 nm (77 K) for [Ru(NH 3) 5DMABN] 3+ complexes, which is the first example for an Ru(NH 3) 5L system. The four emission bands at 555, 595, 635 and 690 nm which occur in the [Ru(bipy) 2-Cl(DMABN)] + spectrum are members of a vibrational progression with Δν ≈ 1175 cm −1 and they could be assigned to the excited states with electron localization on either the bipyridyl or the dimethylaminobenzonitrile ligand, i.e. [Ru III(bipy - (bipy)Cl(DMABN)] + or [Ru III(bipy) 2Cl-(DMABN - )] + respectively.