Hydrogen bonding evolution and efficient blue light emission in a series of Zn-based organic–inorganic hybrid metal halide crystals

Abstract

The influence of hydrogen bonding on spectroscopic properties is one of the fundamental issues in the field of luminescent organic–inorganic hybrid metal halides (OIMHs). We design and prepare three OIMHs, namely, crystals 1, 2 and 3, using 2,2′-bipyridine and ZnCl₂ as starting materials. From crystals 1 to 3, the hydrogen bonding environment surrounding the 2,2′-bipyridinium cations gradually weakens, with both the dihedral angle and the number of hydrogen bonds around them decreasing progressively. Correspondingly, the blue emission belonging to the S₁ → S₀ transition of the three crystals gradually increases, with crystal 3 exhibiting the strongest blue light emission and a photo-luminescence quantum yield reaching 34.10%. In crystal 1, the dense hydrogen bonding environment of the 2,2′-bipyridinium cation results in an obvious energy transfer from S₁ to T₁. This reduces the population of the S₁ state, thereby leading to weaker blue light emission. In crystals 2 and 3, the weaker hydrogen bonding environment and smaller spatial distortion of organic cations weaken or even prevent energy transfer between S₁ and T₁, thereby enhancing blue light emission. These findings provide new insights for exploring novel luminescent OIMHs and developing more effective means of regulating their luminescence performance.