Synthesis and Theoretical and Photophysical Study on a Series of Neutral Ruthenium(II) Complexes with Donor-Metal-Accepter Configuration.

In order to construct a new type of ruthenium(II) terpyridine complexes with activated triplet metal-centered ( 3 MC) states, as well as stabilized triplet metal-to-ligand charge transfer ( 3 MLCT) states, conducive to fine emissive performances, Ru-1 , Ru-2 , Ru-3 , and Ru-4 were synthesized. Compared with the [Ru(terpyridine) 2 ] 2+ prototype (0.25 ns), this series of ruthenium(II) terpyridine complexes exhibit lengthened excited state lifetime (43.3 ns for Ru-1 , 52.7 ns for Ru-2 , 43.6 ns for Ru-3 , and 53.4 ns for Ru-4 ). Interfragment charge transfer analysis illustrates the electron transfer direction of the four complexes, manifesting their intramolecular charge transfer characteristic. When excited, their lowest-lying triplet states are assigned as 3 MLCT based on spin-density surface distribution. The singlet excited states and 3 MLCT states were thoroughly studied by UV-visual absorption and nanosecond time-resolved transient absorption spectra, respectively. Photoluminescence spectra revealed their weak broadband near-infrared emission at room temperature and red phosphorescence at 77 K. The low molecular weight and the good thermal stability make Ru-1 and Ru-2 suitable for vaporization coating, while the fine solubility in common organic solvents makes Ru-3 and Ru-4 suitable for solution processing. Furthermore, the intrinsic electroneutrality and favorable energy levels endow them with new potential to be applied in the optoelectronic field.