Understanding the effect of hydrogen bonding on the structural transition and emission properties in zero-dimensional hybrid metal halides: (3,5-DMP)3BiX6 (X = Cl, Br, I).

Zero-dimensional lead-free organic-inorganic metal halides (OIMHs) have emerged as excellent optoelectronic materials with diverse photophysical properties owing to their versatile structures and impressive broadband emission properties. Understanding the effect of hydrogen bonding on the structural distortion and emission properties is crucial for tuning the optoelectronic properties in these OIMHs. Herein, we have synthesized three new Bi-based 0D OIMH compounds with the chemical formula (3,5-DMP)3BiX6 (X = Cl, Br, I). Hydrogen bonding-induced structural transition from the orthorhombic P212121 to the P21212 space group is observed by replacing Cl- with Br- or I- in (3,5-DMP)3BiX6 (X = Cl, Br, I). Under UV light excitation, the Cl-compound displays a bright and broad orange photoluminescence (PL) emission band at ∼610 nm with a photoluminescence quantum yield (PLQY) value of 27.3%. Upon changing the halide to Br-, the emission peak shifted towards higher energy with a very weak blue emission band at ∼440 nm (PLQY = 0.8%). Stronger hydrogen bonding-induced polyhedral distortion in (3,5-DMP)3BiCl6 facilitates the formation of self-trapped excitons (STEs) and enhances the luminescence properties with higher PLQY. Furthermore, a white light-emitting diode (WLED) was fabricated using the Cl-compound, which displayed a CRI value of 85.0 and a CCT value of 5219 K. This study investigates the effect of variation of halide ions and the hydrogen bonding interaction on the structural distortion and PL properties of these Bi-based OIMHs, thereby providing a reference for the correlation between hydrogen bonding-induced structural variation and PL efficacy.