Ligand topology tunes energy and character of emissive triplet states in stannylenes

Abstract

In the last decades, phosphorescent or photoactive complexes with earth-abundant transition metals have gained huge attention. On the contrary, heavy main group elements with similar properties are rare, in particular group 14 complexes in the oxidation state + II, e.g. tetrylenes. The excited state properties have remained mostly undiscussed and general design concepts for excited state properties─as established for transition metal complexes─are lacking. The present study offers a conceptional topological approach for understanding and addressing specific excited state properties of main group complexes, exemplary discussed by the Sn(t−Bupdpt–Bu) complex 1 with the dianionic pincer-type ligand [t−Bupdpt–Bu]2– (H2t–Bupdpt–Bu = 2,6-bis(3,5-di-tert-butylpyrrol-2-yl)pyridine). 1 shows red triplet ligand-to-metal charge transfer (3LMCT) phosphorescence in the solid state. Emission intensities of solid 1 vary in an unusual manner with temperature. The obtained experimental results are underpinned and interpreted with detailed (SOC-TD)DFT calculations. The investigation of 1 in solution was prevented by formation of a bridged dimer 2. The present results are put into context with the few reported studies on the photophysics of stannylenes to achieve a deeper general understanding of the photophysics of this class of complexes.