Metal Halide Regulated Photophysical Tuning of Zero‐Dimensional Organic Metal Halide Hybrids: From Efficient Phosphorescence to Ultralong Afterglow

Abstract The photophysical tuning is reported for a series of tetraphenylphosphonium (TPP) metal halide hybrids containing distinct metal halides, TPP 2 MX n (MX n =SbCl 5 , MnCl 4 , ZnCl 4 , ZnCl 2 Br 2 , ZnBr 4 ), from efficient phosphorescence to ultralong afterglow. The afterglow properties of TPP + cations could be suspended for the hybrids containing low band gap emissive metal halide species, such as SbCl 5 2− and MnCl 4 2− , but significantly enhanced for the hybrids containing wide band gap non‐emissive ZnCl 4 2− . Structural and photophysical studies reveal that the enhanced afterglow is attributed to stronger π–π stacking and intermolecular electronic coupling between TPP + cations in TPP 2 ZnCl 4 than in the pristine organic ionic compound TPPCl. Moreover, the afterglow in TPP 2 ZnX 4 can be tuned by controlling the halide composition, with the change from Cl to Br resulting in a shorter afterglow due to the heavy atom effect.