Emission Tuning of Group 13 DPP‑ Pincer Complexes via the Heavy Atom Effect of the Metal Ion and the Halide Ligands

We report on the synthesis, structural characterization, and the optical properties of a family of nine complexes (DPP)MX 2 (M = Al, Ga, In; X = Cl, Br, I; DPP = 2,5‐di(pyridine‐2‐yl)pyrrolide) of group 13 elements. According to time‐dependent density functional theory (TD‐DFT) calculations, the energetically low‐lying electronic excitations of these complexes have dominant π→π* and intraligand charge transfer character, with the flow of electron density from the pyrrolide donors to the pyridine acceptors of the DPP − ligand. All complexes display pure fluorescence at room temperature, while (DPP)AlI2 , (DPP)GaI 2 and the indium complexes are dual fluorescence and phosphorescence emitters at cryogenic temperatures. We observe an increase in phosphorescence emission intensity with increasing atomic number of both the heavier group 13 metal ion and the halide ligands. In a glassy frozen matrix at 77 K, emission quantum yields of up to 92% are obtained.