Long-lived higher excited state luminescence from new ruthenium(II)–allenylidene complexes

Resonance Raman spectra of heteroatom substituted ruthenium(II)-allenylidene complexes, obtained by irradiation into the second electronic absorption band, clearly prove the d(Ru)→π*(CCC) MLCT character of the corresponding electronic transition. The complexes are not significantly luminescent at room temperature, but in solvent glasses at 77 K, emission is observed. Only some of the complexes studied are luminescent upon irradiation into their lowest-energy absorption band. The striking finding of this study is that almost all complexes are luminescent on irradiation into their second absorption band. The emission was shown to originate from a higher lying 3MLCT state, which shows that internal conversion to the lowest excited state is very inefficient in these complexes.