A Near-Infrared Luminescent Cr(III) <i>N</i>-Heterocyclic Carbene Complex
Robert W. Jones, Rory A. Cowin, Iona I. Ivalo, Dimitri Chekulaev, Thomas M. Roseveare, Craig R. Rice, Julia A. Weinstein, Paul I. P. Elliott, Paul A. Scattergood
Abstract
High Resolution Image Download MS PowerPoint Slide Photoluminescent coordination complexes of Cr(III) are of interest as near-infrared spin-flip emitters. Here, we explore the preparation, electrochemistry, and photophysical properties of the first two examples of homoleptic N -heterocyclic carbene complexes of Cr(III), featuring 2,6- bis (imidazolyl)pyridine (ImPyIm) and 2-imidazolylpyridine (ImPy) ligands. The complex [Cr(ImPy) 3 ] 3+ displays luminescence at 803 nm on the microsecond time scale (13.7 μs) from a spin-flip doublet excited state, which transient absorption spectroscopy reveals to be populated within several picoseconds following photoexcitation. Conversely, [Cr(ImPyIm) 2 ] 3+ is nonemissive and has a ca. 500 ps excited-state lifetime.