Microsecond Photoluminescence and Photoreactivity of a Metal-Centered Excited State in a Hexacarbene–Co(III) Complex

The photofunctionality of the cobalt–hexacarbene complex [Co­(III)­(PhB­(MeIm)3)2]+ (PhB­(MeIm)3 = tris­(3-methyl­imidazolin-2-ylidene)­(phenyl)­borate) has been investigated by time-resolved optical spectroscopy. The complex displays a weak (Φ ∼ 10–4) but remarkably long-lived (τ ∼ 1 μs) orange photoluminescence at 690 nm in solution at room temperature following excitation with wavelengths shorter than 350 nm. The strongly red-shifted emission is assigned from the spectroscopic evidence and quantum chemical calculations as a rare case of luminescence from a metal-centered state in a 3d6 complex. Singlet oxygen quenching supports the assignment of the emitting state as a triplet metal-centered state and underlines its capability of driving excitation energy transfer processes.