Pnicturesque Luminescence : The Photophysical and Emissive Properties of Dipyridine Pyrrolide Group 15 Diiodide Complexes

Abstract

The synthesis, characterization, and photophysical properties of a family of pnictogen complexes Pn(DPP)I2 bearing dipyridine pyrrolide (DPP−) ligands and with As, Sb, and Bi as the central atom Pn are reported. Slight but systematic trends arising from the variation in the atomic number are apparent in NMR and UV–vis spectra. As confirmed by time‐dependent density functional theory calculations, the electron‐rich DPP− ligand endows the energetically lowest‐lying electronic absorption band with partial DPP‐to‐Pn charge–transfer (ligand‐to‐metal charge transfer) character. All complexes are phosphorescent at cryogenic temperatures with high phosphorescence quantum yields of Φphos = 50.8 to 83.9% and lifetimes in the range of tens of microseconds. In accordance with the heavy atom effect, merely As(DPP)I2, the lightest representative of the three complexes within this work, displays weak fluorescence. It also possesses the shortest phosphorescence lifetime and the highest quantum yield for 1O2 generation. This is attributed to a higher degree of covalent character of the Pn‐ligand bonds and increased orbital overlap as well as larger iodide contributions to the LUMO.